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HISTORICAL GEOLOGY LECTURE, PAGE 1
I. Introduction
A. Geology
- the study of the Earth
1. Physical Geology
- study of the Earth's materials, such as minerals and rocks, and the various physical and
chemical changes that occur on its surface and in its interior
2. Historical Geology
- history of the planet and its life forms from its origin to the present
B. The Birth of Modern Geology
1. James Hutton (1726 - 1797)
- Scottish gentleman farmer and geologist; the "Father of Geology"
- formulated concept of "Uniformitarianism"
a. Uniformitarianism
- "the present is the key to the past"
- the Earth is shaped by daily, mundane processes
- the Earth is very old
- believed that "great catastrophes" have only minor influence
2. Charles Lyell (1797 - 1875)
- English Geologist, wrote Principles of Geology (the first volume appeared in 1830)
- his influential popularization of Hutton's principles influenced generations of geologists
3. More recent studies use the concept of Actualism
a. Actualism
- apply studies of modern processes to ancient rocks
- the processes that now shape the Earth were similar in the geologic past, although the rate of
change may vary
- recognizes that "catastrophes" can have powerful influence on the Earth
4. Geologic Time Scale
- the Earth is 4.6 billion years old
- the subdivisions of the time scale are based primarily on the predominant life forms living
during specific times
II. Minerals and Rocks
A. Mineral
- naturally occurring, inorganic, homogeneous, crystalline solid; more than 90% of rock-forming
HISTORICAL GEOLOGY LECTURE, PAGE 2
minerals are silicates (contain silicon, oxygen and one or more metals)
1. Chemical Composition of Minerals
a. Elements
- fundamental components, cannot be broken down to simpler substances by ordinary chemical
processes
- there are 88 naturally occurring elements
- the 8 most common are Oxygen (O), Silicon (Si), Aluminum (Al), Iron (Fe), Calcium (Ca),
Sodium (Na), Potassium (K) and Magnesium (Mg); comprise 98% of the Earth's Crust
b. Atoms
- fundamental units of elements
Nucleus - positively charged center of mass; includes protons (with mass and a positive charge)
and neutrons (with mass and a neutral charge)
Electrons - with no mass and a negative charge; the number and orientation of electrons
determines chemical behavior
c. Chemical Reactions
- filling of the outer shells of electrons
Ions = charged atoms; atoms with too few or too many electrons; includes cations (positively
charged) and anions (with negative electrical charges)
2. Physical Properties of Minerals
- use color, streak, hardness, crystal form, cleavage, fracture, luster, specific gravity, magnetism,
chemical reactivity, radioactivity, fluorescence, etc. to identify minerals
- see lab manual
3. Mineral Classification
a. Based on dominant anion present in the Mineral
- including silicates, oxides, sulfides, halides, phosphates, carbonates, native elements and
hydroxides
b. Silicate Minerals
- the most abundant chemical group constitute (about 90% of the Earth's crust)
- Silicate Bonding with four oxygen for each silicon; bond directions require a tetrahedral
arrangement of the atoms; the tetrahedra may be isolated or form single chains, double chains,
sheets, or frameworks
- Important Silicate Minerals Include:
HISTORICAL GEOLOGY LECTURE, PAGE 3
Feldspar - a framework silicate found in almost all rock types; constitutes about 50% of the
Earth's crust; includes potassium feldspar and plagioclase feldspar series
Quartz - a very pure framework silicate; common in continental rocks but rare in oceanic and
mantle rocks
c2. Nonsilicate Rock-Forming Minerals
Carbonates - with one carbon and three oxygen atoms; Exs. = calcite, dolomite
Sulfates - with one sulfur and four oxygen; Ex. = gypsum
Sulfides - sulfur combines with some other element (not oxygen); Ex. = pyrite, galena
Halides - one or more metals combine with one or more halogen elements (fluorine, chlorine,
iodine, bromine); Exs. = halite, fluorite
Oxides - one or more metals combine with oxygen; Exs. = magnetite, hematite, corundum
Phosphates - one or more metals combine with phosphate group (1 phosphorous and 4 oxygen
atoms; PO4); Ex. = apatite
Native Elements - mineral consists of a single element; gold, silver, copper, sulfur, graphite,
diamond
B. Rocks
- naturally-formed, solid materials composed of one or more minerals or mineraloids
C. Igneous Rocks
- rocks that solidify from molten material (magma)
1. Melting of magmas
- is due to radioactivity, movement of rock masses into high temperature zones, transfer heat
upward from deep crust or mantle
2. Magma Composition
- ultimate magma composition is especially influenced by type of parent magma (which is
primarily a product of where the magma is formed); mafic magmas (rich in iron and magnesium)
are characteristic of oceanic crust, felsic magmas (rich in silica) are characteristic of continental
crust
- magmas change composition primarily through fractionation (remove crystals from magma
chamber which alters magma composition)
3. Emplacement of magmas is due to lithostatic ("rock") pressure, pressure due to increased gas
volume, tectonism ("mountain-building"), and stoping (magma surrounds and engulfs crystals or
HISTORICAL GEOLOGY LECTURE, PAGE 4
rocks)
4. Intrusive (Plutonic) Igneous rocks
- rocks that solidify beneath the earth's surface
- magma cools slowly and rocks form large crystals
- Examples = peridotite, gabbro, diorite, and granite
5. Extrusive ("Volcanic") Igneous Rocks
- solidify at or near the Earth's surface
- forms from lava (magma flows onto Earth's surface) or tephra/pyroclastic material (magma is
blown onto Earth's surface)
- Examples = basalt, andesite, rhyolite, tuff, agglomerate
D. Metamorphic rocks
- rocks formed from pre-existing rocks by solid state transformation in response to change in the
physical or chemical environment
1. Contact Metamorphism
- occurs in country rock bordering igneous intrusion
- typically created under relatively low pressure, high temperature
- types of rocks include marble, quartzite, hornfels and some ore deposits
2. Regional metamorphism
- occurs on a regional scale due to orogenies (mountain-building events) triggered by plate
tectonics
- sequence of rocks formed under greater temperature and pressure includes mudstone -> slate ->
phyllite -> schist -> gneiss
E. Sedimentary Rocks
- rocks formed from consolidation of loose sediment, formed by chemical precipitation, or rocks
consisting of secretions or remains of plants and animals
- most important rocks for interpreting Earth history
1. Sedimentary rock is product of :
a. Provenance
- pre-existing rocks from which sediment forms and effects of weathering on sedimentary
composition
b. Process
- what happens during transportation, deposition and after deposition
2. Transport of Sediment
a. Agents of transport
HISTORICAL GEOLOGY LECTURE, PAGE 5
- wind, water, ice, gravity
b. Physical Transport
b1. Physical Load
- sedimentary particles carried by current
- forms Clastic or Detrital Rocks (conglomerates, sandstones, siltstones, mudstones)
b2. Dissolved (Chemical) Load
- dissolved ions carried by water; deposited when chemical or physical changes concentrates
solutes and cause them to precipitate
- form Chemical Rocks such as Carbonates (limestone, dolomite) and Evaporites (halite,
gypsum)
3. Sedimentary texture
- size, shape and arrangement of grains
a. Sedimentary Grain Size
a1. Wentworth Scale
- describes size of sedimentary particles
- includes clay, silt, sand and larger size particles
- size of particles transported depends on type of transporting agent and energy of transport
b. Sorting
- range of particle sizes in a sediment
Well sorted- particles of similar size\
Poorly sorted - wide variety of grain sizes
- Sorting depends on type of sedimentary transport: Gravity and glaciers = poorly sorted; Water =
well sorted; Air = most selective sorting
c. Shape
c1. Roundness (Angularity)
- degree of curvature of the corners of the particles;
- depends on type of parent material and degree of sediment transport
c2. Sphericity
- degree to which a particle approximates the shape of a sphere
- typically depends upon the degree of sediment transport
4. Sedimentary Structures
HISTORICAL GEOLOGY LECTURE, PAGE 6
- multigrained features formed during or after accumulation of sediment and before lithification
a. Primary Sedimentary Structures
- form as sediment is being deposited
a1. Stratification
- accumulation of sedimentary particles in horizontal layers
a2. Massive beds
- thick and uniform; form under constant conditions or where bedding is destroyed by organisms
or dissolution
a3. Graded bedding
- grain size increases or decreases from base to top due to changing current velocities
a4. Cross-Bedding
- layers are inclined
- cross-bedding is used to determine ancient current (paleocurrent) direction
b. Secondary (Postdepositional) Sedimentary Structures
- form after sediment deposition, usually due to groundwater interaction with buried sediments
and rocks
b1. Nodule
- irregular, round, flat structure formed by filling voids in sediment
b2. Geodes
- hollow, subspherical structures; form around water-filled pocket by crystals growing inward
b3. Concretions
- mineral segregations that replace or force aside the surrounding sediment
5. Lithification
- transformation of sediment into sedimentary rocks
a. Rocks are composed of:
a1. Particles
- clastic rocks are often made of quartz; also feldspar, rock particles
- Limestone particles include fossils (most important), pellets (invertebrate feces), oolites (sandsize concentrically-ringed carbonate particles) and intraclasts (carbonate mud "rip-ups")
a2. Matrix
- fine-grained material deposited with particles
- clay in clastic rocks
HISTORICAL GEOLOGY LECTURE, PAGE 7
- carbonate mud (micrite) in limestones
a3. Cement
- transported in solution by groundwater and precipitates between grain particles after they are
deposited
- often calcite (termed "sparite" in limestones) or silica (especially quartz)
a4. Pores
- void space between sedimentary particles
b. Diagenesis
- physical, chemical and biologic changes that occur after deposition and before metamorphism
- includes effects of compaction, cementation and recrystallization
III. The Sedimentary Archives
A. Sedimentary Environments
- portion of the earth's surface with distinctive physical, chemical and biological characteristics
1. Facies
- body of sediment or rocks with distinctive characteristics
2. Environmental Analysis
Determination of Ancient Sedimentary Environments Utilizes:
a. Physical Criteria
- including shape of the deposit, rock type (lithology), textures (grain characteristics),
sedimentary structures, fining/coarsening upward in sedimentary grain size
b. Geochemical criteria
- especially isotopic ratios of elements
c. Biological criteria
- fossil content
d. Walther's Law
- the vertical sequence of rocks may reflect the horizontal succession of environments/facies
Transgression - relative rise in sea level
Regression - relative drop in sea level
------------------------------------------------------------
HISTORICAL GEOLOGY LECTURE, PAGE 8
THE FOLLOWING ARE COMMON NON-MARINE (TERRESTRIAL) SEDIMENTARY
ENVIRONMENTS:
B. Soils
- largely product of biological weathering; with rock debris and humus (= decaying organic
matter)
1. Factors that Influence Soil Formation
a. Type of Parent Rock
- influence the type of materials present, amount of fractures, and permeability (ability of fluids
to flow through the system)
- granite often produces sand-rich soils; basalts often produce clay-rich soils
b. Time
- as time progresses and with more weathering soils often become more alike
c. Climate
- affects precipitation and vegetation, which greatly influences soil characteristics
2. Ancient Soils (Paleosols) and Environments:
a. Wetland Paleosols
- often gray, organic-rich
b. Tropical Paleosols
- often with aluminum-rich bauxites or red laterites
c. Arid paleosols
- often red; with shrink-swell clays and mudcracks; often with duricrusts (mineral layers that
accumulate at the soil's upper surface due to capillary action during evaporation, and consist of
silica, carbonates or iron)
C. Lacustrine (Lake) Environments
- landlocked body of water occupying some kind of basin due to faulting, crustal warping, or
glaciation
- controlled by water circulation, salinity and temperature (climate factors), biological factors and
provenance ("source") of sediments
1. Clastic Lake Deposits
- often exhibit a circular morphology, with sand and gravel outside (near the shore) and mud in
middle of lake facies
- lakes typically produce cyclical, often repetitive sedimentary units
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2. Carbonate Lake Deposits
- are most typical of subtropical to tropical climates
- precipitate limestones, dolomites and often contain stromatolites (carbonate algal structures)
3. Playas
- broad shallow depressions in desert regions which may be covered by thin sheet of water
- often with evaporite deposits such as gypsum and halite
D. Fluvial Environments
Rivers - major transporting and depositional agents for continental sediments
1. Meandering Rivers
- with high sinuosity
- these are perennial rivers (they typically flow year-round), with substantial base flow (base flow
is the water contributed by groundwater)
- often produce fining-upward facies with nonmarine fossils; there is often considerable
sandstone in the channel, with deposits of shale (and paleosols) on the floodplain
2. Braided Streams
- interlaced network of low sinuousity channels
- braided streams are due to seasonal "flashy" discharge; often form in temperate mountains, arid
regions and areas with monsoon-influenced climates
- often create a broad, sheet-like morphology; they are usually coarse-grained and typically with
poorly-sorted sediments; fossils are rare
E. Semiarid Areas (Steppes) and Deserts
1. Desert
- areas with less than 25cm rainfall per year
- most deserts are situated at 25° - 30° latitude (due to global circulation patterns in the
subtropics producing high-pressure, low-moisture conditions)
- often with Interior Drainage (where rivers drain into central desert depressions rather than
flowing to the sea)
2. Semiarid Area (Steppe)
- interior continental areas with 25-50 cm rainfall; grassy vegetation
3. Desert Facies Include:
a. Wadis/Arroyos
- "dry washes"; often with braided stream-like features
b. Alluvial Fans
- cones radiate downslope from the point where streams emerge from rocky highlands
HISTORICAL GEOLOGY LECTURE, PAGE 10
- like braided stream deposits but wedge-shaped and with debris flows
c. Sand Dunes
- hill of sand deposited by wind (eolian deposits)
- sand dunes consist of well-sorted coarse silt/fine sand; they have a steep slip face and gentlydipping windward face
- sand dunes typically form thick, crossbedded quartz sandstones
F. Glaciers
Glacier - system of flowing ice that originates on land through the accumulation and
recrystallization of snow
1. Continental glaciers
- Continental glaciers are large, thick, continental- or subcontinental-size glaciers that have been
very important during the Earth's "Ice Ages"
- continental glaciers have both depositional facies (form tillites, composed of glacial deposits
termed till) and erosional facies (often form unconformity surfaces and glacial striations due to
the weight of the ice eroding the landscape)
- continental glaciers are often associated with a combination of fluvial, lacustrine, eolian and
shallow marine environments
------------------------------------------------------------------THE FOLLOWING ARE COMMON MARINE SEDIMENTARY ENVIRONMENTS:
G. Deltas
- depositional body of sand, silt and clay formed where a river discharges into a body of standing
water
- usually cone-shaped, coarsens upward in grain size, and with cyclothems (repetitive
sedimentary sequences alternating from marine- to non-marine deposition)
H. Barrier - Backbarrier Complexes
1. Barrier islands
- elongate islands built by large waves
- barrier islands are composed of sand, gravel, and/or shell debris
- barrier islands are separated from the mainland by lagoons or bays
2. Backbarrier complex
- depositional environments situated between a barrier island and the mainland
- examples include bays and lagoons
3. Sedimentology of Barrier Facies
a. "Surf-side" of Barriers
HISTORICAL GEOLOGY LECTURE, PAGE 11
- beaches are often sandy; they are typically well sorted, cross-bedded and are quartz-rich
- seaward from beaches, facies shift to silt and clay
b. Sheltered Sides of Barriers (Backbarrier Complexes)
- wave action is typically insignificant in lagoons and bays
- chief influences on backbarrier sediments are tides, organisms and climate
- usually organic-rich muds are the prevalent sediment type
I. Tidal-influenced Environments
- sea marginal areas subject to effects of tidal fluctuations (tides are due to Moon-Sun gravitation
on oceans)
- lithology often consists of oolites (sand-size grains of limestone), stromatolites (algal-built
structures), skeletal debris, coal, and evaporites
- sedimentary structures often consist of repetitive fining-upward sequences of sand, silt and clay
J. Organic Reefs
- solid but porous limestone structure standing above the surrounding seafloor and constructed by
living organisms (often with skeletal material, especially corals)
- with a wide variety of morphologies, from isolated Patch Reefs to continuous Barrier Reefs
K. Marine Shelves
1. Types
a. Continental Shelves
- submerged, relatively flat, continental margins (that represent the "true" edges of the continents)
- shelf edge averages approximately 130 meters water depth
b. Epeiric (Epicontinental) Platforms
- broad, shallow sea over continental area
- not common now but was important during periods of major rise in sea level (Example =
Cretaceous Period)
2. Terrigenous shelves
- with land-derived sediments
- sand/gravel nearshore, silt and clay facies offshore
- fining upward in grain size (transgressive sequence) or coarsening upward (regressive
sequence)
3. Carbonate Shelves
- form in tropical/subtropical environments
- create thick limestone sequences
L. Continental Slopes
- slope seaward of continental shelf
HISTORICAL GEOLOGY LECTURE, PAGE 12
- lower limit 500-5000m
- often with turbidites (graded beds deposited when dense, sediment-charged turbidity currents
slow down); carve submarine canyons and deposit deep sea fans
M. Pelagic Deposits
- deep marine deposits accumulated due to vertical sedimentation
- usually consist of Oozes (with microscopic silica or carbonate shells derived from planktonic
organisms) or clay-rich facies
IV. Stratigraphy
- study of rock layers (strata)
Lithostratigraphy and Biostratigraphy have been the major ways in which Relative Geologic
Time (sequencing geologic events) has been established
A. Lithostratigraphy (Physical Stratigraphy)
- defines rock units on the basis of their physical features (i.e. lithologic features)
1. Stratigraphic Laws
a. Superposition
- in series of undisturbed strata, the oldest bed is on the bottom
b. Original Horizontality
- sedimentary units are originally deposited in horizontal layers
- if the layers are not horizontal, the rocks have been deformed
c. Cross-cutting Relationships
- a unit that cuts across another unit is younger than the unit it cuts across
d. Inclusions
- a rock included within another unit is older than that unit
2. Formal Rock Units
- in decreasing order, includes Supergroup - Group - Subgroup - Formation - Member - Bed
- are separated by Contacts (the boundaries between different rock units)
a. Formation
- formations are the basic mapping units in stratigraphy
- a formation must have mappability (typically mapping is done using air photos) and lithologic
constancy (rocks should be of similar type in a given formation)
- Formation names are designated by local geographic names and are capitalized
b. Member
HISTORICAL GEOLOGY LECTURE, PAGE 13
- subdivision of a formation
- often only have local significance
c. Beds
- smallest rock-stratigraphic unit
- beds are informal units, and therefore their names are usually not capitalized
- beds may have economic significance (Coal bed, oil sand, etc.) or used in mapping ("key beds"
or "marker beds" are used for correlation of strata)
d. Groups
- assemblage of 2 or more successive formations
- formations lumped together to form groups are related by lithology (rock type) or by position
with reference to unconformities
3. Defining Formal Rock Units
a. Conformities
- contacts between rocks which exhibit continuous depositional histories
- contacts are typically defined at the boundaries between differing lithologies or textures
b. Unconformities
- unconformities are gaps in the rock record due to erosion or nondeposition; unconformities
often form contacts between groups or formations
b1. Angular Unconformity
- surface separating tilted or folded strata from overlying undisturbed strata
b2. Disconformity
- unconformity between essentially parallel strata
b3. Paraconformity
- unrecognizable in outcrop without the use of fossils, absolute dating, etc.
b4. Nonconformity
- erosion surface between sedimentary and igneous/metamorphic rocks
4. Correlation
- matching stratigraphic sections of the same age
B. Biostratigraphy ("Stratigraphic Paleontology")
1. Biostratigraphic Unit
- body of rocks delimited from adjacent rocks by their fossil content
- fossils are often used for Correlation
HISTORICAL GEOLOGY LECTURE, PAGE 14
a. Biozone
- basic unit of biostratigraphic classification
- based on the distribution of Index Fossils (fossils characteristic of key formations; should have
short time span, wide geographic range, independent as possible of facies, abundant, rapidly
changing and with distinctive morphology)
b. Range Zones
- plot stratigraphic range of fossil(s)
Taxon Range Zone – represents the total horizontal and vertical range of a taxon
Concurrent range zone - overlapping ranges of specified taxa
- Taxon and Concurrent Range Zones are the major types of biozones
2. Major Fossils used in Biostratigraphy
- best are pelagic [planktonic (floating) or nektonic (swimming)] forms
V. Geologic Time
A. Absolute (Actual) Dating Techniques
- dates geologic events in terms of years before present
1. Methods that Depend on Radioactive Decay of one element to another
a. Radioactivity
a1. Isotopes
- forms of an element (with the same number of protons), but they have a different number of
neutrons
a2. Radioactive Decay
- atoms change to another element by releasing subatomic particles and energy; parent isotope
decays to daughter isotope at a constant rate
a3. Radiometric Dating
- measure amount of parent materials relative to their daughter products
Half Life - time required for isotope to decay to half its original amount
a4. Notation
Kiloannum (plural = Kiloannum; kilo an) = Ka = thousands of years in the radioisotopic time
scale
HISTORICAL GEOLOGY LECTURE, PAGE 15
Megannum (plural = Meganna; mega an) = Ma = millions of years in the radioisotopic time
scale; M.Y. (or m.y) = millions of years, without reference to the radioisotopic time scale
Gigannum (plural = Giganna; giga an) = Ga = billions of years in the radioisotopic time scale
a5. Common Isotopes Used for Radiometric Dating
Carbon-14/Nitrogen-14 = Half Life of 5.73 Ka; used to date organic materials; typically restricted
to objects less than 50 Ka
Uranium-238/Lead-206 = Half Life of 4.47 Ga; mostly used to date zircon grains in igneous and
metamorphic rocks
Potassium-40/Argon-40 = Half Life of 1.25 Ga; often used to date volcanic igneous rocks
b. Fission Track Dating
- when uranium 238 decays it emits subatomic particles at a constant rate; this damages the
surrounding crystals, producing fission tracks
- determine track density to date (usually for sites greater than 100,000 years)
2. Methods that require calibration by radioactive or chemical means
a. Magnetic Stratigraphy
a1. The Earth's Magnetic Field is due to the motion of the liquid, iron-rich outer core (it
behaves like a bar magnet to form a north and south magnetic pole)
a2. Magnetic Reversal
- reversal of polarity in Earth's magnetic field; is recorded in iron-rich igneous and sedimentary
rocks
Normal Interval = polarity same as today
Reversed Polarity = polarity opposite to todays
a3. have constructed Paleomagnetic Polarity Scale based on magnetic reversals and "tied" with
absolute dates
b. Changing ratios of Isotopes (Strontium, Sulfur, Carbon, Oxygen) in rocks and shells of
marine fossils
- are tied to absolute dates
c. Thermoluminescence (TL)
- measures the number of electrons caught up in defects in the crystal structure of minerals;
HISTORICAL GEOLOGY LECTURE, PAGE 16
measures time elapsed since electrons were last "drained" from the "traps" (due to burning,
exposure to sunlight, etc.)
- rocks heated in the past release energy (light) when reheated; the more light that is released
during reheating, the older the rock
VI. Geologic Time Scale
A. Chronostratigraphy
- subdivision of rocks considered solely as the record of a specific interval of geologic time
1. Ranks of Time-Stratigraphic Units (Time-Rock Units)
a. Eonothem
- highest ranking chronostratigraphic unit
- includes the Phanerozoic and Precambrian (Proterozoic and Archean) Eonothems
b. Erathem
- subdivisions of an eonothem
- commonly consist of several adjacent systems
c. System
- fundamental unit of worldwide Time-Stratigraphic classification
- usually based on local section and then correlated world-wide on basis of fossils
- the names of systems have diverse origins and all types of endings (Cambrian, Cretaceous,
Jurassic, Tertiary)
d. Series
- next in rank below system
- some of worldwide extent, others provinces
- commonly known by geographic names (Comanchean, Gulfian) OR Upper, Middle, Lower
(Lower Cretaceous, Upper Cretaceous)
e. Stage
- next in rank below series; groupings of biozones
- names often based on rock-stratigraphic units; often divided into substages
2. Time Units Versus Chronostratigraphic Units
Time Unit Chronostratigraphic Unit
Eon
Eonathem
Era
Erathem
Period
System
Epoch
Series
Age
Stage
HISTORICAL GEOLOGY LECTURE, PAGE 17
B. Geologic Time Scale
- Learn the Geologic Time Scale Provided!
VII. Life on Earth
A. Paleontology
- study of ancient life
Fossil = any evidence of prehistoric life
1. Paleozoology
- study of fossil animals
a. Invertebrate paleontology
- study of fossil invertebrates (animals without a vertebral column)
b. Vertebrate paleontology
- study of fossil vertebrates (animals with a vertebral column)
2. Paleobotany
- study of fossil plants
a. Palynology
- study of pollen and spores
- often also include study of marine one celled "plants"; i.e. acritarchs, dinoflagellates, diatoms,
calcareous nannoplankton/coccoliths, etc.
3. Micropaleontology
- study of small fossils
- includes many groups mentioned under palynology and also foraminifera, radiolaria, chitinozoa,
graptolites, pteropods (gastropods), ostracods (crustaceans), conodonts
4. Paleoecology
- study of ancient environments and how ancient creatures relate to their environment and other
organisms
B. Prerequisites/Preferred Conditions for fossilization:
1. Relatively abundant organisms
2. Presence of hard parts
HISTORICAL GEOLOGY LECTURE, PAGE 18
3. Avoid chemical and physical destruction
- rapid burial, typically within a relatively low energy depositional environment
- preservation often depends on oxidation/reduction (Eh) and acidity/alkalinity (pH)
characteristics in the environment; plants are often preserved within acidic and reducing
conditions; calcareous shells and bones are typically preserved in non-acidic environments
C. Types of Fossil Preservation
1. Unaltered Fossil Preservation
a. Unaltered Soft Parts
- unstable organic compounds are preserved such as carbon, hydrogen and oxygen
- rarely preserved; sometimes within permafrost (Ex. = mammoths) or glaciers, mummification
in dry caves (ground sloths), tanning by humic acids in peat (Ex. = "bog people"), within
anaerobic aqueous environments (such as the "limnic stagnation deposits" in the Eocene German
"brown coal" at Messel), within oil seeps, and in amber
b. Unaltered Hard parts (Durapartic Preservation)
- preserve original calcium carbonate or calcium phosphate "hard parts" such as bone (ex. = La
Brea tar pits, California), shells, "coralline" algae; durapartic preservation is relatively rare
2. Altered Hard Parts
- this includes the most common fossil preservation types
a. Petrification includes:
a1. Cellular Permineralization (Impregnation)
- percolating groundwater introduces minerals (ex. = silicates, carbonates, iron compounds,
phosphates) into the pore spaces (especially permineralize calcareous shells with calcite; also
wood and bone often permineralized)
a2. Recrystallization
- change form and/or size of original crystal structure; Ex. = conversion of the calcium carbonate
mineral aragonite to calcite (calcite has the same composition as aragonite, but a different
crystalline structure); recrystallization often destroys fossil detail
a3. Replacement
- percolating groundwater dissolves hard parts and replaces them with different minerals;
Minerals involved include carbonates, silicates, iron oxides such as hematite and "limonite",
pyrite, and collophane
b. Carbonization
- volatile components (hydrogen, oxygen, nitrogen) decrease and the outline of the animals is
preserved as a carbon film; often combines with petrification
HISTORICAL GEOLOGY LECTURE, PAGE 19
3. Traces of Animals
a. Molds and casts
Mold - impression of skeletal (or skin) remains in an adjoining rock
External mold - impression of outer side
Internal mold (steinkern) - impression shows form or markings of inner surface
Cast - original skeletal material dissolves and cavity (mold) fills with material
b. Ichnology
- study of trace fossils (Ichnofossils = tracks, trails and burrows of organisms)
- are very useful since trace fossils were created when the organism was alive (therefore, trace
fossils reflect ancient ecologies and habits of organisms)
- trace fossils are often used to determine rate of deposition and the original characteristics of the
sedimentary environment in which the organism lived
Bioturbation Texture - sedimentary texture due to disturbance of sediments by organisms
(bioturbation); often consists of dense, contorted, truncated or interpenetrating burrows or other
traces of indistinct form
- the major use of trace fossils is for determining ancient water depths (Paleobathymetry)
c. Coprolites
- fossil excrement of animals; may contain undigested remains of food
D. Groups, Names and Relationships
Taxonomy - process of classification and naming organisms; typical classification of organisms
is by their relationship to one another (= "natural" classification)
- the classification of organisms has traditionally used the Linnaean System, formulated by
Carolus Linnaeus in the 1700's (Many biologists and paleontologist are now abandoning the
Linnaean System, due to the influence of Cladistic Taxonomy, which groups animals on the basis
of their shared derived characteristics)
1. Taxa (classification categories; singular = taxon) in the Linnaean System
a. Domain
- in some recent classifications, constitutes the highest taxonomic category
- often include the Domains Archaea/Archaebacteria, Bacteria/Eubacteria, and Eucarya
HISTORICAL GEOLOGY LECTURE, PAGE 20
b. Kingdom
- in many classifications is the highest taxonomic category
- there are typically 5 to 6 recognized kingdoms [Monera (often classified as Domain or
Kingdom Archaea/Archaebacteria and Domain or Kingdom Bacteria/Eubacteria); Domain
Eucarya includes the Kingdoms Protoctista (Protista), Fungi, Animalia (Metazoa), and Plantae
(Metaphyta)]
c. Phylum
d. Class
e. Order
f. Family
g. Genus
- group of interrelated species; plural = genera
h. Species
- fundamental unit of taxonomy
- a species is considered to represent a population of individuals that can interbreed and produce
viable offspring
- because paleontologists typically do not know what individuals interbred in the fossil record,
most fossil species are based on their morphology (form)
E. Chemical Cycles in Earth System History
Chemical Reservoirs - bodies of key elements and compounds in the Earth system that shrink or
expand as fluxes between them change
- these reservoirs are influenced by the following:
1. Photosynthesis and Respiration
Photosynthesis - process by which plants use the energy of sunlight to produce sugars from
carbon dioxide and water; oxygen is a by-product of this process
Respiration - opposite chemical reaction versus photosynthesis; organisms oxidize sugars in
order to release their energy
2. Carbon Dioxide and Oxygen Cycles
- if no dead plant tissue is buried, it decomposes and carbon dioxide returns to the atmosphere
- if dead plant tissue is buried (such as in swamps or anoxic marine environments), it upsets the
balance between photosynthesis and respiration (with the amount of carbon dioxide in the
atmosphere shrinking and with increase in oxygen levels)
HISTORICAL GEOLOGY LECTURE, PAGE 21
- weathering of minerals removes carbon dioxide from the atmosphere (enhanced by mountain
building, warm climates, high rates of precipitation, and more vegetation)
- the initial spread of forests during the Devonian intensified weathering, depleted the
atmospheric reservoir of carbon dioxide; this reduced greenhouse warming and probably
contributed to the cooler climate conditions and formation of the Late Paleozoic "Ice Age"
3. Methane Cycles
- methane is a powerful greenhouse gas
- when global warming melts masses of methane hydrate on the seafloor, the addition of methane
to the atmosphere produces further global warming
4. Negative Feedback in Carbon Dioxide and Global Warming Cycles
- when climate warms, chemical weathering accelerates (extracting carbon dioxide from the
atmosphere) and the amount of evaporation increases on the ocean (which further accelerates
weathering on land, extracting more carbon dioxide from the atmosphere)
5. Submarine Volcanism versus Seawater Chemistry, Mineralogy and Types of Organisms
- seawater circulating around mid-oceanic ridges transfers calcium to the seawater; magnesium is
extracted from the water and becomes locked in the rocks [therefore with more seafloor
spreading there is a rise in sea level (because more rocks are produced that displace the water)
and a decrease in the magnesium/calcium ratio (more magnesium is extracted from seawater)]
- with increased marine volcanism, the low magnesium/calcite ratios produce "Calcite Seas", in
which calcite forms oolites and marine cements and organisms with calcite skeletons become
successful reef builders (the lowest magnesium/calcite ratio of the Phanerozoic was during the
Cretaceous, which contains much more "chalk" than any other system)
- when the total volume of volcanics at mid-oceanic ridges is low, aragonite and high-magnesium
calcite is more abundant; "modern" types of corals, with aragonite skeletons, are more abundant
during these periods of Earth history
VIII. Evolution and Extinction
Evolution = (1) historical changes in structure, function and adaptation (2) genetic changes and
processes of selection and population dynamics
Adaptations - specialized features of organisms that provide useful functions (adaptation
involves the “remodeling” of old organs); adaptations are how organisms cope with changing
environmental conditions, invade new environments, and function more efficiently in a given
environment
A. History of Evolutionary Theory
1. Jean Baptiste de Lamarck (1744-1829)
- French naturalist; developed theory now known as Lamarckism (theory of inheritance of
acquired characteristics)
HISTORICAL GEOLOGY LECTURE, PAGE 22
2. Thomas Malthus (1766-1834)
- English clergyman and economist; wrote "Essay on the Principle of Population"; introduced
concept that population exhibits exponential growth, whereas food production exhibits linear
growth; population expands to limits set by famine, war and disease
3. Alfred Wallace (1823-1913)
- codiscoverer of the theory of natural selection independent of Darwin; also a prominent
zoogeographer
4. Charles Darwin (1809-1882)
- most naturalists of his time were "special creationists"; as ship's naturalist on the H.M.S. Beagle
(1831-1836) developed the foundation of his theory of evolution; Read Malthus' Essay on
Population; Wrote "The Origin of Species by Means of Natural Selection" in 1859
Darwin's facts and deductions include:
- organisms tend to increase in numbers exponentially
- in spite of the tendency to progressive increase, the number of individuals within a species tend
to remain approximately constant.
- Deduction: Since more young are produced than can survive there must be a competition for
survival ("Struggle for Existence")
- all organisms vary; some variations are inherited
- some individuals fail to survive, others live to reproduce (Natural Selection)
Summary of Darwinian Evolutionary Theory: New species arise from preexisting ones as a
result of natural selection acting on inherited variations
B. Evidence for Evolution
1. Geographic distribution of organisms
- different animals are found in similar environments worldwide
- isolated environments (especially islands) with similar animals with diverse form and habits
2. Anatomy
a. vertebrate embryos are very similar, especially during their early stages of development
b. Homology
- organs in different animals with the same origin but different function
c. Vestigial Organs
- organs with no function (resemble working organs in other creatures)
- examples include the pelves of whales and boa snakes, the "dewclaws" of dogs, and the "extra
toes" of horses
HISTORICAL GEOLOGY LECTURE, PAGE 23
3. Artificial Selection
- domestic breeders preserve certain biological features and eliminate others
- similar to Natural Selection
4. Genetics
- study of mechanisms of inheritance
- founded by Gregor Mendel (1822-1884)
a. Particulate Inheritance
- presence of hereditary factors (genes) that retain their identity while being passed on from
parent to offspring
- Genes are segments of DNA (they are concentrated in chromosomes in the cell nucleus)
b. Mutations
- chemical changes in genetic features
- provide most variability on which natural selection operates
c. Sexual Reproduction
- sex cells (gametes = egg and sperm) unite to form a zygote (this process is termed Sexual
Recombination)
- this yields new combinations of chromosomes/genes and greater variation
Populations = groups of interbreeding individuals
Gene Pool = total genetic components of populations
- origin of new species (Speciation) is probably by isolating a population
d. Genetic Paleontology
- almost all molecular paleontology studies have been performed using DNA from mitochondria
(mtDNA), cell structures that supply energy for metabolism
- the extracted DNA is compared to other DNA sequences (from a relative, a particular
population, or a species) to identify an individual or the population the sample came from
- these studies have been used to determine the genetic similarity (and evolutionary relationships
of species)
- random mutations substitute various amino acids in molecules or nucleotide sequences for
DNA that is more or less directly proportional to time (therefore there may be "Molecular
Clocks", which have proven useful in determining the timing of evolutionary divergence in
organisms)
5. Paleontology
- studies of fossils reveal phylogenies (evolutionary histories and relationships)
C. Evolutionary Theories Concerning Rate of Change
HISTORICAL GEOLOGY LECTURE, PAGE 24
1. Phyletic Gradualism
- rates of evolution are regular
- is Darwinian Evolutionary Theory
2. Punctuated Equilibrium
- first proposed by Niles Eldredge and Stephen Gould during the 1970's
- says that evolution occurs in fits and spurts separated by long periods of little change
- problem in testing (sudden appearances in fossil record may be due to immigration rather than
rapid speciation)
- problem in classification [no classification system can show intermediate forms (only
"species")]
D. Adaptive Radiation
- rapid origin of many species from a single ancestral group
- often follows immediately after origin of group (with adaptive breakthroughs) or after a mass
extinction
E. Social Darwinism
- proponents used writings of Charles Darwin, and especially Herbert Spencer, to urge laissezfaire economic policies to weed out the "unfit, inefficient, and incompetent"
1. Herbert Spencer
- English author and philosopher (1820-1903)
- believed that "rational men" should not interfere with the laws of evolution, and poorer classes
should be "eliminated" by their "unfitness"
- his views were popular among conservative politicians, millionaires, etc.
2. Ernst Haeckel
- German zoologist and evolutionist (1834-1919)
- believed that Darwin's theory of evolution was the answer to all questions of science,
philosophy, ethics, religion and politics (the Monist Philosophy)
- was considered a national hero in Germany for his influential views that the German "master
race" must "outcompete inferior peoples"
- Adolf Hitler in Mein Kampf ("My Struggle"), published in 1925, took the title of his book from
Darwin's phase "the struggle for existence" as translated by Haeckel
3. Francis Galton
- English scientist and philosopher (1822-1911)
- founded the Eugenics Movement (sought to bring about social improvement through selective
breeding of humans)
- adopted by the Nazis in their Lebensborn ("Fountain of Life") Movement, an attempt by
Heinrich Himmler and the German S. S. to create a "master race" of "Aryans", and "clear" vast
areas of land inhabited by "inferior peoples" to provide a place for "Aryan" habitation
F. Extinction
HISTORICAL GEOLOGY LECTURE, PAGE 25
- total disappearance of a taxon
- most likely in species with small populations and those that live in limited geographic areas
(population size related to trophic level and body size with carnivores most likely to become
extinct and small herbivores least likely)
1. Types of Extinction
a. Background Extinction
- probability of extinction is approximately constant through the life of a particular group but
rates vary from group to group
- therefore there is a "normal background rate" of extinction
b. Mass Extinction
- there are about half a dozen Phanerozoic episodes of major extinction
Theories for Mass Extinction Include:
Environmental Deterioration - climate changes (Exs. = cooling trends, drop in sea level, oxygendepleted deep ocean water rises onto continental shelves, violent volcanism) cause mass
extinctions
Stochastic Processes
- says that origin and extinction of organisms is probabilistic (like a "flip of a coin")
- computer programs randomly generating "artificial" phylogenies are much like "natural" clades
- an example of a stochastic event would be extinction by a bolide impact (no matter how
perfectly adapted the organism is to its environment, it will still die as a result of this catastrophic
event)
Man – has impacted ecosystems for the past 11,000 years (?)
IX. Continental Drift and Plate Tectonics
A. Continental Drift
1. Alfred Wegener
- German meteorologist and polar explorer (1880-1930)
- in 1915 wrote The Origin of Continents and Oceans
- proposed that all continents were part of a huge supercontinent (Pangaea)
- Pangaea "broke up" 200 million years ago to form Laurasia (North America and Eurasia) and
Gondwana (South America, Africa, Antarctica, India)
2. Wegener's Evidence Included:
a. Fit of Continents
HISTORICAL GEOLOGY LECTURE, PAGE 26
- continental coastlines form a puzzle-like fit (later geoscientists found that edges of continental
shelves form an even better fit)
b. Fossil Evidence
- distribution of the fossil plant Glossopteris and the reptile Mesosaurus on the Gondwana
continents indicates that they were once joined
c. Paleoclimatology
- distribution of glacial deposits (tillites), ancient deserts and reefs, and coal deposits indicate the
continents were one joined and were at different paleolatitudes
d. Geologic Evidence
- matching of rock types between modern continents indicate that the continents were once joined
3. The Demise of Continental Drift Theory
- Wegener believed that the continents were like "boats" (plowing through the ocean basins) or
"sleds" (sliding on top of oceanic rocks), with the continental crust moving upon the mantle
- there is no evidence that the continents moved through or over the ocean basins; the crust and
uppermost mantle are joined together as a rigid unit
B. Plate Tectonic Theory
- theory that Earth's crust is divided into a series of large lithospheric plates
1. Lithosphere
- brittle material forming the large plates; consists of Earth's crust and upper portion of mantle
- lithosphere rides on the moving asthenosphere (ductile material separating the lithosphere from
the lower mantle)
2. Types of lithospheric plates
a. Oceanic (Simatic) Plates
- formed from basalt being produced along Rift Zones at mid-oceanic ridges; have high specific
gravity and therefore form basin areas
b. Continental (Sialic) Plates
- granitic composition and form continental areas
3. Evidence for plate tectonics
a. fit of continents
b. climatic criteria
c. paleontologic support
HISTORICAL GEOLOGY LECTURE, PAGE 27
d. petrologic (rock) evidence
e. measurements from space - indicate that plate movement averages 2-9 cm/yr
f. Paleomagnetism
Seafloor Spreading - the process through which plates diverge and new lithosphere is created at
midoceanic ridges
- youngest rocks are nearest to the midoceanic ridges
- during seafloor spreading the polarity of the Earth's magnetic field alternates, which is
preserved as bands of normal and reversed polarity "stripes" in the magnetized basaltic crust
"Polar Wandering Curves" - due to movement of lithospheric plates the magnetic poles appear to
change in position; used to reconstruct the ancient positions of the continents
5. Plate Movements
a. Craton - tectonically passive part of a continent
b. Continental Divergent Boundaries
- the mantle material rises as a Thermal Plume, the crust cracks and forms a “Triple Junction";
two of the "arms" form a Rift Valley; the "failed arm" that does not open forms a large trough
(Aulacogen) which receives sediments
- rifting produces basalt and igneous rocks of mixed composition; weathering of the surrounding
continental granitic rocks produces feldspar-rich arkosic sandstones (arkoses) which are shed into
the rift valley
c. Rift valley opens wider and forms a Proto-Oceanic Gulf
- with restricted water circulation; in arid climates evaporites may form in these basins (such as
the Jurassic-age Louann Salt deposits of the Gulf of Mexico)
d. Further Rifting creates Ocean Basins
- age of the ocean floor is determined by radiometric dating of basalt, study of microfossils, and
correlation of magnetic "stripes"; oldest ocean rocks are about 200 million years old
- continued continental divergence often creates a passive continental margin (with wide
continental shelves upon which wedges of land-derived terrigenous sediments are deposited and
carbonate platforms build)
- Oceanic sedimentation is controlled by:
Nearness of tectonism - volcanism tends to be most dominant along plate boundaries
Carbonate compensation depth (CCD) - depth at which carbonate dissolution equals carbonate
production, due to acidic water in deeper parts of oceans; below the CCD within ocean basins,
mostly clay and chert is deposited as carbonate sediments dissolve
HISTORICAL GEOLOGY LECTURE, PAGE 28
e. Convergent boundaries
- lithospheric plates collide
- tectonically active boundaries, typically with relatively narrow continental shelves
e1. Suture Belts
- usually formed due to collision of continental lithospheric plates; creates sedimentary basins
and/or huge mountain ranges (Exs = Himalayas, Urals)
e2. Ophiolite Suites
- series of rocks exposed when plates are Obducted (oceanic plate overrides continental or
another oceanic plate); provides a cross-section of the Earth's crust and upper mantle
e3. Subduction
- Convergent plate junctions where oceanic plate "dives" beneath a continental plate and is
destroyed
- often contain Melanges (large bodies of broken and sheared rock)
- Subduction zones are located by study of deep-seated earthquakes (Benioff Zones; up to 700
km depth) that are caused by the shattering of the subducted plate
f. Transform (Shear) boundaries
- boundaries in which plates slide past one another (Ex. = San Andreas Fault, California)
- transform faults offset mid-oceanic ridges at perpendicular angles; develop due to different
rates of seafloor spreading and due to fracturing of a round object (the Earth's surface)
6. Hot Spots and Mantle Plumes
- chains of seamounts and volcanic islands are often formed by lithospheric plates moving over
"fixed" mantle plumes or hot spots
- "weight" of the islands produced by hot spots causes isostatic sinking and the ultimate
formation of coral atolls and flat-topped submarine guyots
- hot spot traces may show the direction of plate movement (Example = the orientation of the
Hawaiian Islands indicate that the Pacific Plate is moving toward the northwest)
- hotspots/mantle plumes may also form under continents (Ex.= Yellowstone National Park)
7. Microcontinents
- small pieces of continental crust that have fragmented and moved by sea-floor spreading
- a modern example is the island of Madagascar, located east of Africa
8. Exotic Terranes
- microcontinents that collide and become attached to larger continental margins (Ex.= parts of
Western North America and Appalachia)
X. Origin of the Universe and the Archean Eon
HISTORICAL GEOLOGY LECTURE, PAGE 29
A. Origin of The Universe
- the universe is believed to be approximately 10 - 20 billion years old
Age Estimation is Based Upon:
1. Star Observations
- observation of star clusters and interpretation of nucleosynthesis (study of element formation,
especially in massive stars) estimates that age of universe is from about 15 to 20 billion years old
2. Hubble's Law (Law of Redshifts)
- the velocities at which galaxies move away from us are proportional to their distance from us;
more and more remote galaxies will have greater and greater speeds of recession
- based on the Law of Redshifts, it is believed that the universe is 10 to 20 billion years old
(recent studies indicate possibly 13.7 billion years old)
a. According to Hubble's Law, the universe is expanding
b. At the "beginning of time" all energy and matter in the universe was crowded together at a
single point
c. The Big Bang - the event that created the Universe; it generated the expanding motion that
we observe today
- the first stars and galaxies began forming within one billion years after the Big Bang
B. Solar Nebula Hypothesis
- Solar System probably began as a slowly rotating cloud of gas and dust
- gases and dust condensed and clumped to form planetesimals; planetesimals aggregated to form
planets and their satellites (moons); dates of oldest rocks on the Earth's Moon and the oldest
Meteorites cluster at about 4.5 Ga
- rocky and metallic material condensed to form planets in the hot inner portion of the Solar
System; lighter gases and ice condensed in the cold outer portions of the Solar Nebula to form
huge planets
- late impact of planetesimals cratered the surfaces of the planets and moons, and may have tilted
the rotational axes of some planets
- some planetesimals survive to this day as asteroids and comets
C. The Planets
1. The Terrestrial Planets
- small, dense "rocky" planets including Mercury, Venus, Earth and Mars
- lie in inner part of Solar System
- not much hydrogen and helium; Moons absent or few
2. The Jovian Planets
- giant planets consisting primarily of hydrogen, helium, methane and ammonia gases and liquids
HISTORICAL GEOLOGY LECTURE, PAGE 30
(and water)
- include Jupiter, Saturn, Uranus and Neptune
- low density; ring systems and many moons present
3. Pluto and the "Minor Planets"
- Pluto completes its highly elliptical orbit (which is out of the ecliptic plane) in approximately
248 years; axis of rotation nearly lies in it's orbital plane
- made of rock mixed with ices (water, nitrogen, methane)
- Pluto and it's "moon" Charon are now considered to be "Minor Planets"; they are probably
remnant planetesimals from the birth of the Solar System
D. Other Solar System Features
1. Comets
- icy bodies (mostly water and carbon dioxide/carbon monoxide ice) less than 10 kilometers
across
- the comet nucleus consists of ice and gases; as comets approach the Sun they begin to vaporize
to form a Coma (cloud of gases) and a tail
2. Asteroids
- irregular-shaped rocky or metallic bodies with diameters from a few meters to 1000 kilometers
- most orbit Sun within the Asteroid Belt between Mars and Jupiter
3. Meteorites
- iron, stony (silica-rich), or stony-iron particles that hit the Earth’s surface; most formed from
broken-up asteroids/planetesimals or material left over from formation of the Solar System
4. Bolides
- a meteorite, asteroid or comet that hits the Earth
- there were many bolide impacts in the early history of the Solar System; this is shown by the
heavy cratering of the Moon (and other Solar System satellites) and "geologically dead planets"
like Mercury
- an asteroid may have struck Earth at the end of the Cretaceous Period (approximately 65
million years ago), stirred up dust and created fires, initiated a "nuclear winter" and caused mass
extinctions (including the dinosaurs)
E. Origin of the Earth's Moon
- probably formed when a Mars-sized body collided with the Earth, splashing material into orbit
- the Moon is not a chunk of Earth; it formed almost entirely from the mantle of the impacting
body (which accounts for the differing proportions of iron and magnesium versus the Earth)
- this material coalesced to form the Moon (which has a feldspar-rich outer layer and very small
metallic core)
- the core material of the impacting planet combined with the Earth's core
F. Origin of the Earth
HISTORICAL GEOLOGY LECTURE, PAGE 31
1. Initial Earth Differentiation into Layers
- heat from bolide impacts and radioactive decay produced a molten planet, in which the most
dense material sank toward the center and the least dense rose toward the surface (produced an
iron core and a silicate-rich mantle)
- the less dense silicates floated to the surface, forming a "magma ocean", which cooled to form a
silicate-rich crust (this was a precursor to the oceanic crust of the modern world)
2. Crustal Origin
a. Primitive Crust
- was of mafic composition (with abundant ferromagnesian minerals; the crust was derived from
ultramafic mantle material)
b. Continental Crust
- formed at least 4.1-4.2 Ga, and was produced by partial melting of the primitive mafic crust
- during the Archean the Earth had higher heat flow and abundant "hot spots"
- igneous processes associated with hot spot activity produced felsic crust by partially melting the
mafic parent material (a similar process is occurring now in Iceland, where felsic volcanics form
along the Mid-Atlantic Ridge)
- small Archean continents (Protocontinents) formed; weathering and metamorphism generated
additional felsic crystalline rocks
- the oldest crustal rocks from Canada are dated at approx. 4.04 Ga; metamorphosed sediments in
western Australia have zircon grains dated at 4.4 billion years old; this is the official beginning of
the Archean, which includes about 45% of Earth History
c. No large continents in the Archean
- broad blocks of crust older than 3 billion years are absent in Preccambrian Shields (strong heat
flow from below prevented protocontinents from coalescing to form large continents)
G. Precambrian Tectonics
1. PreCambrian Shields
- igneous and metamorphic cratons form the nuclei of continents; these are surrounded by
younger rocks
- rocks of similar age occupy distinct orogenic belts
- there is at least one PreCambrian Shield area on every continent (ex.= Canadian Shield)
2. Archean Rocks
a. Types of rocks present
Greenstones - belts of low-grade metamorphic rocks with chlorite, epidote and green amphibole;
probably formed by metamorphism of volcanic belts along margins of small continents/ ocean
basins
HISTORICAL GEOLOGY LECTURE, PAGE 32
Granulites - quartz- and feldspar-rich, high-temperature metamorphic rocks; occur between
greenstone belts; most formed during the Kenoran Orogeny at 2.5 Ga
Deep-water sedimentary rocks - graywackes (clay- and feldspar-rich sandstones) and deep marine
mudstones are common; metamorphosed turbidites are common (deposited in forearc basin and
other environments along subduction zones); nonmarine and continental shelf deposits are rare
(therefore there were evidently no large continents during the Early Archean)
Oldest Banded Iron Formations (ex. = Isua, southern Greenland) dated at approx. 3.65-3.8 Ga;
alternating iron oxides and quartz (originally chert) layers; silica probably derived from
submarine volcanoes; fomation of iron may have been influenced by the presence of bacteria
b. Formation of Large Cratons began during late Archean
- heat flow from the Earth's interior diminished and allowed protocontinents to coalesce
- in Southern Africa there is evidence of a large craton at 3.1 - 2.7 Ga (with a thick sequence of
sedimentary rocks, the Witwatersrand strata, containing placer gold- and uranium-bearing
braided stream deposits; glacial tillites are found in the Pongola Basin at 2.9 Ga)
H. The Atmosphere was Formed By:
1. Degassing of the Earth's Interior
- an initial atmosphere was probably formed during differentiation, then "swept away" when the
early Solar System was cleared of debris by a strong "Solar Wind" (charged particles moving
away from the Sun)
- volcanic activity then produced a second atmosphere of water vapor, hydrogen, hydrogen
chloride, nitrogen, carbon dioxide, carbon monoxide (and secondary chemical reactions in the
atmosphere produced methane and ammonia)
2. From Comets/"Space Ice"
- comet-like material supplied ammonia, methane, water vapor, etc. to partially create the
atmosphere
3. Photosynthesis
- early photosynthetic organisms, such as blue-green algae (cyanobacteria), created oxygen
- but there was evidently little "free" oxygen present in the Precambrian
I. The Oceans
- the Earth's interior degassed, gases condensed in the atmosphere during Earth cooling, and
precipitation formed and fell to Earth to form oceans
- the salinity of the Ocean was created by weathering rocks on land
- seawater has varied little in salinity since the Early Archean (although the relative proportions
of dissolved ions has varied significantly)
- the Early Archean ocean was probably much warmer than that of today due to the presence of
abundant radioactive elements in the Earth's crust and the "Greenhouse Effect"
HISTORICAL GEOLOGY LECTURE, PAGE 33
I. Origins of the Biosphere
1. Organisms
- ordered (i.e. with cellular organization) living creatures
- "life" is a series of chemical reactions, using carbon-based molecules, by which matter is taken
into a system and used to assist the system's growth and reproduction, with waste products being
expelled
- life forms pass on their organized structure when they reproduce
2. Origins of Life
a. The Earth During the Archean Eon
- equable conditions for prebiotic evolution could have existed on Earth as long ago as 4.4 Ga
- Archean Earth was dominated by oceanic lithosphere with volcanic islands and small
microcontinents
- large amounts of CO2 may have led to a Greenhouse Effect, with atmospheric temperatures up
to 100°C or more (therefore there were no polar icecaps; with permanently stratified stagnant
iron-rich deep ocean waters and with wind-mixed iron-poor surface waters)
- hot springs, submarine hydrothermal systems, and heated wind-mixed layers of the oceans may
have been areas where prebiotic evolution occurred
b. Origins of Life
b1. Depends upon the synthesis of Carbon
- once carbon is synthesized, all other biogenic molecules may be formed (Organic Molecules are
complex, carbon-based molecules)
- elements most prominent in organic molecules are carbon, hydrogen, oxygen and nitrogen
b2. Cellular Structure
b2a. Cell
- a "container" filled with organic and inorganic molecules (= Protoplasm); the cell contains:
b2b. Proteins
- built from amino acids; proteins are used as "building materials" and for chemical reactions
b2c. Nucleic Acids
- includes Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA); provide information for
the structure of the organism and the means to pass on this information in reproduction
- DNA carries the genetic code of an organism, providing information for its growth and
metabolism; it has the ability to replicate itself in order to pass this information on to
subsequent generations
HISTORICAL GEOLOGY LECTURE, PAGE 34
- RNA has several functions (carries genetic message of DNA to sites; assembles amino acids
into proteins; acts as a catalyst for chemical reactions), and because of this versatility was
probably the nucleic acid present within the earliest life forms (this earliest ecosystem is often
termed the "RNA World"); but RNA was eventually replaced by DNA as the genetic code (as
DNA is a more stable molecule)
b2d. Organic Phosphorous Compounds
- found in small amounts; transform light or chemical fuel into energy
c. The Formation of Proteins
c1. Amino Acids
- mixture of methane, ammonia, hydrogen and water vapor (or nitrogen, carbon dioxide and
water vapor) in the presence of electricity or ultraviolet light leads to the production of amino
acids
- some meteorites also contain amino acids
- production of amino acids must take place in an anaerobic (devoid of free oxygen) environment
c2. Proteins
- removing water from amino acids yields Polypeptides (protein-like chains)
- when polypeptides cool they form Microspheres (cell-like structures)
3. Kinds of Organisms
a. Prokaryotes
- single-celled organisms with their DNA loosely organized within the cell, are not bounded by a
membrane into a nucleus and they lack chromosomes
- meiosis is absent (see discussion under Eukaryotes below)
- range from 0.3 to 20 microns in size
- are often termed Monerans
- often divided into two Domains (or Kingdoms):
a1. Domain/Kingdom Archaea/Archaebacteria
- superficially similar to Eubacteria but differ greatly in their molecular (especially RNA)
sequences
- include the methanogens (tend to be found in highly saline environments), sulfur-metabolizing
bacteria and sulfate-reducing bacteria (found around hydrothermal vents)
- probably included the oldest life forms, which were probably thermophilic ("heat-loving")
autotrophs (used molecular hydrogen, carbon dioxide and sulfur compounds to produce energy,
with optimal growth at temperatures from 70° to 110°C); possible environments of origin
include hot springs, heated ocean waters, and hydrothermal vents
a2. Domain/Kingdom Bacteria/Eubacteria
- contain the most commonly recognized or "true" bacteria and cyanobacteria
- evolved both thermophilic autotrophs in heated environments and photoautotrophs in shallow
HISTORICAL GEOLOGY LECTURE, PAGE 35
marine environments
- life originated at least as early as 3.5 Ga ago, as indicated by (mostly) Eubacteria
Evidence Includes:
a2a. Megascopic Stromatolites
- Stromatolites are laminated structures formed by blue-green algae (cyanobacteria)
- the earliest Stromatolites come from South Africa and Australia (dated about 3.0 to 3.45 Ga)
a2b. Permineralized Microfossils
- filamentous kerogen-rich microfossils similar to cyanobacteria occur in Australian cherts dated
at about 3.5 Ga
a2c. Biologically Produced Organic Matter
- organic carbon-13 values from the 3.0 to 3.55 Ga-old South African and Australian sediments
are similar to those of modern cyanobacteria and photosynthetic bacteria
XI. The Proterozoic Eon (Late Precambrian)
A. Proterozoic Eon Tectonics (2.5 Ga - 543 Ma)
1. Development of the First Cratons
- the first cratons of modern proportions formed about 3 Ga (see discussion in Archean section
above)
2. Plate Tectonics Begins
a. Plate Convergence and Tectonism
- 2 Ga ago with earliest evidence of plate tectonism
- The Wopmay System of Canada is a body of deformed rocks that represent the formation of the
first mountain system (the Wopmay Orogen); consists of a fold-and-thrust belt of sedimentary
rocks (representing non-marine to deep marine clastics and carbonates), a metamorphic belt and
belt of igneous intrusions
b. Continental Accretion
- continental accretion and growth occurs during mountain-building (orogenesis) by suturing an
island arc or microcontinent to a large craton along a marginal subduction zone OR by
compression and metamorphism of sediments that have accumulated along continental margins
(Orogenic Stabilization)
- the Wopmay System may have enlarged the Slave Craton by both suturing of a small plate and
orogenic stabilization
- Orogenic Processes and regional metamorphism may alter preexisting rocks beyond recognition
and resets their radiometric clocks so that the age of the crust can not be determined (this process
HISTORICAL GEOLOGY LECTURE, PAGE 36
is termed Remobilization); this has been a problem in studying the earliest tectonic events on
Earth
- following continental accretion, the first extensive carbonate platforms and shallow-water
terrigenous deposits appeared
c. Plate Rifting in the Proterozoic
- continents can decrease size by erosion (not very significant since it is relatively slow), by
subduction (also not very significant since continents are light-weight and resist being pulled into
subduction zones), or by continental rifting (very important)
- first evidence of continental rifting appeared in what is now eastern North America at about 1.0
to 1.2 Ga, with basaltic lavas extruding along the Great Lakes Region (the Keweenawan
Supergroup; also with alluvial fan conglomerates deposited within down-thrown fault blocks, or
grabens) and extended into the central U. S. (the Mid-Continent Rift); rifting ceased, but not
before the rift belt grew to 1500 kms (900 miles) long and 100 kms (60 miles) wide
d. Creation of Larger Continents Worldwide
- The core area of Laurentia (primarily North America) sutured to the microcontinents of Baltica
(a portion of Europe), northern South America, West Africa, Southern Africa, Eastern Antarctica
and Australia at 1.95 to 1.85 billion years ago and formed a larger craton
- Between about 1 billion and 800 million years ago the landmasses that would later become
Gondwanaland encircled and tectonically sutured to Laurentia (forming a supercontinent
sometimes termed Rodinia)
- the Grenville Orogeny was occurring along the east coast of North America (from eastern
Canada through the Llano Uplift region of Central Texas) at about 1.1 Ga; this was caused by the
collision of eastern North America with what would later become northern South America
e. Rodinia Rifts
- between 800 and 700 million years ago Rodinia rifted apart to form the Pacific Ocean (there are
many failed rifts from Northern Canada to Arizona, including the Belt Supergroup in the
northern United States, that represents this divergence)
f. A Second Supercontinent Forms?
- another supercontinent may have formed by about 550 million years ago, beginning with the
suturing of the microcontinents that would become Gondwanaland (this event is often termed the
Pan-African Orogeny)
- there is some controversy as to whether the supercontinent was fully formed - if not, most of the
Earth's continental crust were certainly clustered close together at this time
B. Proterozoic Climate
1. Early Proterozoic
HISTORICAL GEOLOGY LECTURE, PAGE 37
- Early Proterozoic with widespread glaciation (an example is the Gowganda Formation of
southern Canada, consisting of varved mudstones, tillites and glacial dropstones); also glaciers of
similar age in Wyoming, Finland, southern Africa and India
2. The Vendian Period (610-550 Ma ago) or Neoproterozoic
- the beginning of Vendian Period exhibits the most extensive glaciation in Earth history (the
Varanger/Varangian or Marinoan Glaciation)
- later Vendian with relatively warm global climate, with major marine transgression and
development of extensive shallow marine environments, which led to a greater diversity of
organisms
C. Life in the Proterozoic
1. Prokaryotes
- beginning about 2.2 GA, stromatolites become increasingly abundant (probably because of
increased size of continental shelves)
2. Domain Eucarya
Eukaryotes = single- or multi-celled organisms with chromosomes made of DNA, RNA and
proteins contained within a membrane-bound nucleus
a. Characteristics
- cells range from 3 microns to several millimeters
- with specialized structures (vacuoles, mitochondria, many with chloroplasts) that provide
metabolic functions for the cells
- oxidize sugars as a source of energy
- meiosis present = with two consecutive cell divisions by which the chromosomes are reduced
from the diploid number of somatic cells to the haploid number (half) characteristic of gametes
and spores
- sexual reproduction provides more variation that may potentially enable the species to better
survive environmental changes
- the Domain Eucarya includes the Kingdoms Protista (Protoctista), Fungi, Plantae (Metaphyta)
and Animalia (Metazoa)
b. Origin of Eukaryotes
- the nuclear membrane probably formed by invagination (folding inward) of the cell membrane
- specialized structures (chloroplasts and mitochondria) probably developed from endosymbiotic
prokaryotes living within the cell membrane of archaebacterial prokaryotes
c. The Oldest Eukaryotes
- as oxygen built up in the Early Proterozoic atmosphere, due to the presence of photosynthetic
prokaryotes, the concentration of dissolved oxygen increased in the upper ocean; as a result more
nitrogen was oxidized to form nitrate (NO3-), which is an important nutrient for eukaryotic algae
[Cyanobacteria don't need nitrates, as they can use pure nitrogen (N2) for their metabolism]
HISTORICAL GEOLOGY LECTURE, PAGE 38
- oldest known probable eukaryote is the corkscrew-shaped, cylindrical megascopic colonial alga
Grypania, from a 2.1 Ga-old banded iron formation in Michigan
- organic-walled microfossils of eukaryotic photoautotrophic plankton ("acritarchs") occur in
rocks slightly younger than those containing Grypania
D. Atmospheric Oxygen
- increased dramatically between 2.2 and 1.9 Ga-ago; evidence includes the presence of paleosols
and redbeds, the decrease in uraninite deposits (uraninite is unstable in free oxygen), and increase
in uranium and molybdenum in marine shales (they weathered from the land in the presence of
oxygen and were washed into the oceans)
- increase in atmospheric oxygen was very important for the development of more complex life
forms
1. Banded Iron Formations
- consist of alternating chert and hematite/magnetite layers
- therefore oxidized (ferric) iron formed in marine basins (although there is some debate as to the
original oxygen content in BIF's)
- but Banded Iron Formations disappeared about 1.9 Ga-ago when oxygen content was supposed
to be increasing (BIF's may also be influenced by ocean stratification and therefore this may be
the source of conflicting data, or they may not have contained as much oxygen as some
geologists have claimed)
2. The Ozone Shield
- development of ozone (O3) prevented lethal radiation from reaching the Earth and was of major
importance in the development of life
E. Origin and Diversification of the Metazoa
1. Metazoa (Animalia)
- with specialized cells forming tissues (= metazoan organization)
- tissues are united into organs (except in simplest invertebrates)
2. Vendian Body Fossils and Trace Fossils
a. Tracks and Burrows
- oldest undisputed metazoan traces found in Late Proterozoic rocks (approx. 560 Ma)
- Vendian trace fossil assemblages include feeding burrows, dwelling burrows, crawling and
grazing trails; differ from later Phanerozoic types with Vendian trace fossils smaller and with
shallow penetration into the sediment (i.e, no deep burrowers were present during the
Proterozoic)
b. Ediacara Fauna
- approximately 580-542 Ma; originally from the Pound Quartzite of South Australia; later found
in approximately 25 Late Proterozoic localities worldwide
- Vendian fossil record consists of moderately large, soft bodied invertebrates preserved in well-
HISTORICAL GEOLOGY LECTURE, PAGE 39
aerated shallow marine environments (it is unusual to preserve in this environment during later
Phanerozoic times; Ediacaran preservation is probably mostly due to the absence of predators,
scavengers, deposit feeders, etc. during Vendian times)
- the structure and relationships of Vendian Fossils is greatly debated; hypotheses of their
relationships state that most Ediacara fossils can be placed in modern groups such as jellyfish,
various worm phyla, and arthropods OR the Ediacara fauna have a unique “pancake-like”
organization with a quilted construction to increase surface area; this allowed absorption of
oxygen and organic matter that were dissolved in the water to diffuse through the body wall; if
this is true, Ediacara animals did not have a mouth, digestive system, or respiratory organs
XII. Paleozoic Plate Tectonics and Paleogeography
A. The Proterozoic-Cambrian Transition
- in the late Proterozoic the continents may have been sutured together to form a huge
supercontinent
- during the Late Proterozoic and Early Cambrian most of the Earth's cratons were exposed above
sealevel (with only a few shallow-water limestones at their margins)
B. Cambrian
- by late Cambrian time Gondwana and three smaller landmasses existed, with major portions of
the continents at low latitudes
- Cambrian with progressive flooding of continents by marine transgressions, with land-derived
terrigenous sediments surrounded by shallow-water carbonates and deeper marine deposits
C. Ordovician
- Gondwanaland was situated over the South Pole, with accumulation of large glaciers (and with
a drop in global sealevel, cooling of seas, and a major extinction event at the end of the
Ordovician)
- Laurentia and Baltica were situated closer to the Paleoequator, with accumulation of limestone
deposits (similar to those seen today in the Bahamas)
Taconic Orogeny - Ordovician mountain-building event in eastern North America due to the
suturing of Laurentia with several large islands; this resulted in a shift from carbonate deposition
to deep marine ("flysch" or turbidite) deposition along a subduction zone that was created by this
convergence; the suturing of these "exotic terranes" resulted in the introduction of "foreign" late
Cambrian-early Ordovician fossils into eastern North America
- in western Laurentia there was a passive margin from Cambrian through Ordovician time (with
accumulation of thick clastic and carbonate rock sequences; an example is the Burgess Shale of
British Columbia, Canada (famous for it's fossils - see below)
D. Silurian
- Taconic Orogeny subsides, where erosion of the eastern mountains produced clastic (and later
carbonate) deposits; in the Michigan Basin region large coral-strome reefs dotted shallow
HISTORICAL GEOLOGY LECTURE, PAGE 40
epicontinental seas (and was surrounded by large barrier reefs); by Late Silurian times restricted
flow in the basin led to accumulation of huge amounts of evaporite minerals
Acadian Orogeny - Laurentia collides with Baltica (to the north) and the microcontinent Avalonia
in the south; began in the north during Mid-Silurian time and extended down through the eastern
United States (to form the Carolina Terrane)
E. Devonian
- Gondwanaland is formed, with a large portion of it situated over the South Pole
- Laurentia and Baltica converge by the Late Devonian and form highlands between them;
sediments were shed off the mountains to form the Catskill Clastic Wedge (ranging from nonmarine redbeds, through braided and meandering streams to coastal deltas); there was a mudfloored seaway to the west of the coastal mountains with limestones, reefs and evaporites beyond
- an island arc developed along the western margin of Laurentia, which later collided with the
continental margin (to produce the Antler Orogeny); this was the first important episode of
mountain-building during the Phaneozoic in western North America
- sealevel declined in the late Devonian
F. Mississippian (Early Carboniferous)
- continents were tightly clusered
- sealevel rose, with warm shallow seas spread across broad continental regions within low
latitudes; many limestones were formed
G. Pennsylvanian (Late Carboniferous)
- Gondwanaland moves northward to collide with Euramerica; this creates a mountain range in
southern Europe (the Hercynides) and northwestern Africa (this is called the Hercynian or
Variscan Orogeny) and in North America (the Alleghenian Orogeny, which is in effect a
continuation of the Acadian Orogeny)
- the Alleghenian Orogeny created the Appalachian Mountains, with mountain-building also
extending from Mississippi through Oklahoma and Texas to create the Ouachita Mountains,
Wichita Mountains, Amarillo Mountains and Marathon Uplift; it also resulted in the formation of
the Midland and Delaware Basins in western Texas and New Mexico
- in the southwestern U. S. the region became transformed into a series of uplifts and basins
bounded by faults; examples include the Front Range and Uncompahre Uplifts (often referred to
as the "Ancestral Rocky Mountains"), and the Paradox Basin to the west (which is filled with
evaporites, due to the rain-shadow influence of the "Ancestral Rockies")
- the formation of Pangaea transforms climate, with cooler conditions resulting in the greatest ice
age of Phanerozoic time
- there were extreme temperature differences between the poles (where continental glaciers
pushed within 30 degrees of the equator on Gondwanaland) and the subtropics (where coal
swamps flourished in North America and western Europe, resulting in the most important coal
resources in the Northern Hemisphere; these coal deposits were formed within cyclothems
(repetitive sedimentary cycles associated with deltas)
H. Permian
HISTORICAL GEOLOGY LECTURE, PAGE 41
- Siberia sutured to eastern Europe, nearly completing the assembly of Pangaea (southeast Asia
was the only landmass not included, which would become attached in the Early Mesozoic)
- suturing created numerous mountain ranges; the result of this mountain-building and the fact
that much of Pangaea was far from moisture-providing oceans led to dry conditions with the
formation of huge dune deposits, extensive red-beds, and evaporites
- the huge Capitan Reef (centered in the Guadalupe Mountains region of west Texas and New
Mexico) grew upward in the shallow seas of the Delaware Basin; the Midland Basin to the east
became infilled with sediment; eventually the Delaware Basin became restricted, resulting in the
deposition of thick evaporite deposits (including the economically-important potash mines near
Carlsbad, New Mexico)
- the drying Permian climate resulted in diminishing coal deposits (except in China and
Australia, which has large Permian coal reserves)
- from Late Permian through Early Triassic time, an orogenic episode centered around Nevada
(the Sonoma Orogeny), with active volcanoes in the island arc area around California
XIII. Life of the Paleozoic
A. The Tommotian Fauna
- often classified as the base of the Cambrian
- first fossils of the "Cambrian Explosion"; first abundant record of hard parts, with thousands of
taxa represented
- the Tommotian Fauna includes "small shelly fossils", or tommotiids, that consisted of distinct
chain mail-like sclerites of calcium carbonate or calcium phosphate that evidently articulated to
form an exoskeleton; there are also mollusc-like shells, sponge spicules, soft corals(?),
fragmentary arthropods, sponge-like archaeocyathans, and shells of brachiopods and brachiopodlike animals
B. The Causes of Metazoan Diversification (the "Cambrian Explosion")
1. Environmental Factors
- end of late Precambrian (Varanginian) glaciation
- development of extensive continental shelf areas and epicontinental seas
- Oxygen increases to 6-10% of present atmospheric levels; development of the ozone layer
allows organisms to leave restricted environments
2. Biological Factors
- microorganisms increase in number and therefore with increase in filter-feeders
- organisms create habitats for other organisms
HISTORICAL GEOLOGY LECTURE, PAGE 42
- secretion of skeletons
- development of hard skeletons of organic or biomineralized (silica, carbonate, phosphatic)
materials
- skeletons were useful for protection, support above the substrate, muscle attachment, guides for
feeding currents, and as supplies of calcium and phosphate nutrients
- calcium carbonate skeletons could not be secreted until oxygen reached approximately 10% of
modern levels (about 2% total atmospheric gases)
C. Development of the First Reefs
- reefs originate in Early Cambrian (dominated by the sponge-like archaeocyathids and
cyanobacteria-formed stromatolites)
- at the end of the Cambrian almost all archaeocyathids became extinct
D. Chengjiang Fauna
- The Chengjiang Fauna (approx. 525-520 Ma) is found in the middle portion of the Early
Cambrian in Yunnan, China
- contains many well-preserved remains of soft-bodied organisms including jellyfish and other
cnidarians, segmented and priapulid worms, arthropods (including the fearsome 6 foot-long
carnivorous Anomalocarids), as well as the earliest fishes
E. The Middle Cambrian Burgess Shale Fauna (ca. 515 Ma)
- Burgess Shale of British Columbia, Canada is dominated by arthropods and several phyla of
"worms", but also many weird forms with no living kin
F. The Late Cambrian Extinction
- there are three periods of trilobite mass extinction in Late Cambrian
- these were probably due to cooling periods
G. The Ordovician Adaptive Radiaton
- all major modern phyla are present by the end of the Ordovician
1. The Ordovician Biota
a. The Ordovician Benthos
- stromatolites (algal structures) decline due to marine herbivores
- trilobites suffered a major extinction at the end of the Cambrian, but became the most abundant
marine invertebrates of the Early Ordovician
- articulate brachiopods, rugose corals (especially horn corals), tabulate corals and
stromatoporoid sponges form calcite reefs (Coral-Strome Reefs)
b. Ordovician Plankton and Nekton
- graptolites became major components of the Ordovician zooplankton
- huge, straight-shelled nautaloid cephalopods, some over 10 feet long, become the top predators
of Ordovician Seas
HISTORICAL GEOLOGY LECTURE, PAGE 43
2. The Ordovician Ecosystem becomes "Filled"
- "ecological crowding", where all the marine niches become filled, prevented further
evolutionary diversification near the end of the Ordovician and the number of species "levelled
off"
3. Mass Extinctions at the End of the Ordovician
- oxygen isotopes indicate a major cooling period (glaciation) and extinction lasting from 0.5 to 1
million years at the end of the Ordovician
- Gondwanaland was over the South Pole, and carbon isotopes also indicate a decrease in
greenhouse gases
- two pulses of extinction occurred; the first event killed off tropical species as the seas cooled;
this was followed by a second event, where cool-water species that took over the seas was killed
by a warming event
H. Life of the Silurian and Devonian
1. Reef Communities
- Coral-Strome Reefs diversified, and some became much larger than their Cambrian-Ordovician
counterparts
- Reef communities were formed in the same types of habitats, and exhibited similar ecologic
evolution (Ecological Succession) as their modern analogues
2. New Swimming Carnivores Evolve
a. Ammonoids
- coiled cephalopod molluscs diversified rapidly within marine environments
b. Eurypterids
- scorpion-like large predators that inhabited brackish and freshwater environments
c. Huge Fish Evolve
- placoderms were the top vertebrate predators of the Devonian (see discussion below)
3. Late Devonian Extinction
a. Glaciation
- tillites show that glaciers were widespread over southern Gondwanaland
- the cooling may have been caused by the great expansion of forest ecosystems in the Devonian;
these may have depleted carbon dioxide in the atmosphere, causing cooler temperatures
b. Extinction of the Coral-Strome Reefs
- most reef-building organisms die out at the end of the Devonian (tabulate corals and
stromatoporoid sponges will never again be important reef-formers)
c. Extinction of Land Plants
HISTORICAL GEOLOGY LECTURE, PAGE 44
- the Late Devonian also had extensive extinction among land plants
I. Late Paleozoic Marine Ecosystems
1. Shift in Reef Ecosystems
- marine ecosystems were very much like those seen in the Late Devonian, but
Magnesium/Calcium ratios rose early in the Carboniferous, with "Aragonite Seas" replacing
"Calcite Seas"
- the shift in ocean chemistry saw the replacement of the old "Coral-Strome Reefs" with reefs
consisting mostly of aragonite-secreting algae and fusulinid foraminiferans; sponges with
aragonite skeletons became imporant Permian reef-builders
2. Life on the Carbonate Sea Floor
- crinoids ("sea lilies") and lacy bryozoans became very important during the early
Carboniferous, extending and filter-feeding above the muddy carbonate seafloor
3. Switch of Top Predators
- the heavy placoderm fishes and huge nautiloid cephalopods were replaced by more mobile
ammonoid cephalopods, sharks and ray-finned fishes
J. Chordates
1. Characteristics
- possess a notochord, a dorsal hollow nerve cord with a shared developmental pattern, an
endostyle organ (equivalent to the thyroid gland of vertebrates), and a tail for swimming (a tail is
a distinct region developed behind the anus)
2. Origin of the Chordates
- chordates may have been derived from hemichordates (both have ciliated gill slits and giant
nerve cells not seen in echinoderms) or another similar echinoderm group OR from
calcichordates (based on interpretation of fossils; calcichordates were a strange echinoderm-like
group with an exoskeleton composed of large plates and had a stem- or tail-like structure)
K. The Vertebrates
1. Characteristics of Vertebrates
- bilaterally symmetrical, usually with a fusiform ("streamlined") shape
- tendency to concentrate sensory organs on the anterior ("front" or “head”) end; a skull is present
which articulates with the vertebral column
- a notochord is present (a long, rod-shaped anti-telescoping structure below the nerve tube)
- vertebrates have a skeletal system made of cartilage (flexible material capable of growth) or
bone (strong material made of irregular, branching cell spaces); the skeleton consists of an Axial
Skeleton (the "backbone") and Appendicular Skeleton (consisting of limb girdles, unpaired fins
[the dorsal, anal, and caudal (tail) fins], and paired fins (the pectoral fins are in front, pelvic fins
behind)
HISTORICAL GEOLOGY LECTURE, PAGE 45
2. The Record of the earliest Vertebrates
a. Middle Early Cambrian (525-520 Ma)
- the Chengjiang Fossil Site, Yunnan Province, southwest China has mostly arthropods but also
the first fishes
b. Late Cambrian Vertebrates
- conodonts (eel-like animals) were the earliest vertebrates with hard tissues (consisting of toothlike structures)
- another group of vertebrates is indicated by isolated pieces of dermal armor from Wyoming and
Greenland (this dermal armor is made from apatite, which is characteristic of vertebrates)
3. Agnathans
- jawless vertebrates; paired fins are absent or poorly developed
The Major Types of Paleozoic Agnathans are:
a. Pteraspidomorphs
- include a couple of poorly-known Ordovician groups represented by pieces of dermal armor,
and the heterostracans
Heterostracans - Ordovician to Upper Devonian jawless fish with partially-developed head
shields and with long, narrow oral ("mouth") plates for capturing prey; these are the earliest
undisputed vertebrates
b. Cephalaspidomorphs
- include the Osteostracans, and a couple of other lesser-known Paleozoic jawless fish
Osteostracans (include the Cephalaspids) are the most common cephalaspidomorphs; Upper
Silurian to Upper Devonian; usually small fish with an undivided bony shield which extended
down the body; the head was dorsoventrally compressed; the eyes were dorsally-placed and with
dorsal and lateral fields ("electric" or pressure-sensitive "sensory" organs?) on top of the head;
they are believed to have been bottom dwellers and "mud grubbers"
4. Evolution of Jaws and Fins
a. Origin of Jaws
- Older theories state that jaws may have been derived from gill arch supports (but embryological
studies indicate some problems with this theory)
- Modern embryological studies indicate that once bones around eyes are formed, a series of
connector genes may have begun making a lower jaw cartilage, perhaps to strengthen the existing
mouthparts
b. Origin of Paired Fins
HISTORICAL GEOLOGY LECTURE, PAGE 46
Fin-Spine Theory – the theory that the primitive fin developed around a movable spine
Fin-fold Theory – the theory that fins originated as lateral folds along the body walls; pectoral
and pelvic fins originated by subdivision of this fold; this is the most widely accepted theory but
fin origins may be a combination of "fin spines" and "fin folds"
5. Placoderms
- typically dorsoventrally compressed Devonian- to Mississippian-age fish with head and trunk
shields (in advanced types the shields were connected by a ball-and-socket articulation)
- placoderms include the large carnivorous Arthrodires and the "arthropod-like" mud-grubbing
Antiarchs
6. Acanthodians
- small fusiform fish from the Ordovician through Lower Permian; all fins except caudal with
spines on anterior edge; upper lobe of tail larger than lower lobe (heterocercal tail)
7. Chondrichthyans
- sharklike fishes
- sharks have cartilaginous skeletons; the skin is covered with dermal denticles including placoid
scales, teeth, claspers and fin spines
Major Types of Paleozoic Sharks include:
a. Symmoriids
- best known Paleozoic sharks (Devonian – Pennsylvanian); with multicusped teeth, a short blunt
"snout"; some species had wierd dorsal fin brushes (for sexual display?)
b. Eugeneodonts (Edestid and Helicoprionid Sharks)
- Upper Devonian to Triassic sharks in which the front teeth tended to form strange whorlshaped cutting devices; the rear teeth usually formed crushing surfaces
c. Xenacanths (pleuracanths)
- primarily freshwater sharks from the Upper Devonian to Upper Triassic; they had a straight
(diphycercal) tail and the teeth usually had two or three pointed cusps
8. Actinopterygians
- bony fish (Osteichthyes) that differ from sarcopterygians in the presence of fin rays (bony, rodlike fin supports)
- found in both freshwater and marine environments from the Devonian to Recent
- possibly originated from the acanthodians
- major evolutionary changes in the skeleton of ray-finned fish include a change in tail (caudal)
fin morphology from an asymmetrical (heterocercal) to symmetrical (homocercal) tail and a shift
in the position of the paired fins where the pelvic fins move forward and the pectoral fins shift to
a higher position on the lateral body wall (this is good for intricate manuevering)
HISTORICAL GEOLOGY LECTURE, PAGE 47
- in primitive ray-finned fish the skull bones are oriented obliquely, with many skull bones
present; the major tooth-bearing bone was the maxilla; primitive ray-finned fish were "biters"
- in more derived fish the jaw becomes more nearly vertical, there are fewer skull bones, and the
anterior-most bone in the upper jaw (the premaxilla) becomes hinged and is pushed forward by
the now-toothless maxilla (this allows the jaws to open wide, and open fast to consume larger
prey and for “suction feeding”)
9. Sarcopterygian Fishes
- bony fish (Osteichthyes) with fleshy lobe fins and cosmoid scales (these scales have sensory
canal systems withing them)
Types of Sarcopterygian Fish Include:
a. Dipnoans
- the lungfish are Devonian to Recent lobe-finned fish in which the teeth typically form crushing
toothplates; the tails are typically straight (diphycercal)
- modern species of lungfish are found in freshwater but extinct types inhabited a wide variety of
environments
- lungfish burrows (for aestivation during dry seasons, where they can survive in a semiinanimate state) are found from the Devonian to Recent
b. Coelacanths
- coelacanths are predominantly predatory fish whose fossils are found in Devonian through
Cretaceous-age rocks, where they lived in both marine and freshwater environments; there is now
only 2 living coelacanth species known (both are marine)
c. Osteolepiforms ("Rhipidistians", in part)
- important fish since they (or a closely related group) gave rise to the amphibians
- osteolepiforms are large, voracious fish that lived from the Middle Devonian to Lower Permian
- the skull bones of osteolepiforms are largely homologous to those of primitive tetrapods; they
also had labyrinthodont teeth (with infolded plicidentine) and had a similar limb and vertebral
structure to early amphibians
L. Land Plants (Kingdom Plantae)
- evolved from the Chlorophyta (grass-green algae)
- possibly represented by plant tissue and spores in Mid- to Late Ordovician (probably lived only
in moist habitats at that time)
- began to become abundant during the Devonian
1. Subkingdom Tracheophyta
- vascular plants [with conducting cells (xylem and phloem) for transporting water and nutrients];
usually possess roots, stems and leaves
The most important divisions are:
HISTORICAL GEOLOGY LECTURE, PAGE 48
a. Division Rhyniophyta (Rhyniopsida) and Psilopsida (Psilophyta)
- oldest-known vascular plants (Middle Silurian); the best fossils are from the Rhynie Chert
(Lower Devonian, Scotland)
- no leaves or roots (therefore with photosynthesis occurring in the outer cells of the stem); with
stems capped by spore-bearing cases
b. Division Lycophyta (Lycopodophyta, Lycopsida)
- includes the modern club mosses and quillworts; also include the arborescent (tree-like)
lycopods that dominated the Carboniferous coal swamps
- the leaves were often strap-like; there were also leaves present in pits on the trunk;
- Examples = Lepidodendron, Lepidophloios, Sigillaria (stems/trunks), Stigmaria (roots),
Lepidophylloides (leaves)
c. Division Sphenophyta (Sphenopsida)
- include the modern horsetails and several extinct groups (Devonian- Recent)
- with scale-like, small leaves arranged in whorls around an above-ground, bamboo-like jointed
photosynthetic stem
- are typically found in swamps, moist woodlands, and along lake edges
- common fossils include Calamites (a Pennsylvanian-age arborescent sphenopsid; some
members were up to 15 meters or more in height) and Annularia (leaf whorls)
d. Division Filicinophyta (Filicopsida, Pteridophyta)
- include ferns and their allies (Upper Devonian - Recent)
- immature fronds unroll (circinate) in most members; usually the leaves are pinnately compound
(the leaves are opposite one another) with spore cases on the leaf undersides
- Tree ferns were large, arborescent ferns (Mississippian - Permian) found in coals swamps (Exs.
= Psaronius, Pecopteris)
- arborescent lycopods, sphenopsids and tree ferns became extinct when the Late Paleozoic coal
swamp environment declined, probably due to climate changes resulting from the formation of
Pangaea
e. "Gymnosperms"
- probably not a "natural" classification group
-"modern" cone-bearing types and glossopterids spread in Permian (probably due to greater
seasonality/aridity)
- gymnosperms (and angiosperms) are characterized by seeds; typically formed by fusion of egg
and sperm nuclei; then develop into ripened ovules (= seeds)
- gymnosperms have no flowers and seeds are not fully enclosed (gymnosperm means "naked
seed")
- the Pteridosperms, or "Seed Ferns" (Devonian – Jurassic) had fern-like compound leaves but
gymnosperm-like seeds and wood; examples include Alethopteris, Neuropteris, and possibly
Glossopteris
M. Land Invertebrates
HISTORICAL GEOLOGY LECTURE, PAGE 49
- earliest fossilized land animals were arthropods
1. Late Silurian (approx. 415 Ma)
- the oldest undisputed arthropods are centipedes and millipedes
2. Middle Devonian of Gilboa, New York (approx. 380-375 Ma)
- represent soil- and leaf litter-dwellers
- most common are spider-like trigonotarbids; also earliest true spiders, oldest terrestrial(?)
scorpions, fungus- and worm-eating mites, first insects (flightless bristletails)
3. Pennsylvanian (approximately 315 Ma)
- with abundant flying insects and first evidence of insects that ate living vascular plants
(indicated by mouthparts and gut contents)
N. Evolution of Land Vertebrates
Tetrapods = "four-footed" vertebrates
1. Origin of the Tetrapods
- may have left aquatic environments due to low oxygen content in the water, population
pressures (seeking food, competition for space, breeding sites, and to escape from predators or
egg-eaters)
2. "Amphibians"
- the earliest tetrapods (four-footed creatures) are from Upper Devonian rocks
Types of Paleozoic "Amphibians" include:
a. Ichthyostegids
- earliest tetrapods but not ancestral to other groups; Upper Devonian to Lower Mississippian
- some of the early tetrapods have as many as 8 toes (Ichthyostega had 7) that were developed
into paddle-like appendages; ichthyostegids were probably largely aquatic and could not fully
support their weight on land
b. "Temnospondyls"
- Mississippian- to Cretaceous-age labyrinthodont amphibians that evolved from osteolepiform
fishes; primitive features inherited from these fish include labyrinthine infolding of dentine,
palatal fanged teeth, vertebrae composed of several centra elements
- often with large, flat heads; examples include the aquatic eryopoids and trimerorhacids; the
terrestrial, armored dissorophids and the metoposaurs (large-skulled aquatic amphibians)]
c. Lepospondyls
- usually small, Mississippian to Permian-age amphibians; may have evolved from early
labyrinthodonts (but with no labyrinthine infolding, no palatal fangs and pits, and no otic notch at
the back of the skull)
HISTORICAL GEOLOGY LECTURE, PAGE 50
- characterized by lepospondylous vertebrae (spool-shaped bony cylinder surrounding the
notochord)
- includes the snake-like aistopods and lysorophids, the eel-like nectridians [Diplocaulus and
Diploceraspis had “boomerang-heads”], and the lizard-like terrestrial "microsaurs"
d. Seymouriamorphs
- have a combination of reptile and amphibian features, and gave rise to reptiles
O. Reptiles
1. Characters of Reptiles:
a. Development of amniote egg
- has a large yolk, a shell, and extraembryonic membranes which protect the egg, supply
nourishment and for gas exchange
Amniotes - probably a monophyletic group; probably originated in the Mississippian
b. Changes in the Skull
- lose several bones in the skull; decrease the size of the bones in the back of the skull, and
lengthen the ones in front
c. Changes in the Skeleton
- develop a more efficient and flexible vertebral column, and an improved limb and ankle
structure
2. Reptile Classification and Radiation
- often based on patterns of openings of the skull roof (termed temporal openings), which
developed behind the orbits
a. Anapsid condition
- no temporal opening; Exs. = captorhinids, turtles
b. Synapsid condition
- lower opening with postorbital and squamosal meeting above; Ex. = mammal-like reptiles
c. Diapsid condition
- two temporal openings present; Exs. = dinosaurs, pterosaurs and ancestral condition of all
modern reptiles except turtles
d. Euryapsid (Parapsid) condition
- upper opening with postorbital and squamosal meeting below; Exs. = plesiosaurs, ichthyosaurs
- derived from the diapsid condition through loss of the lower temporal fenestra
HISTORICAL GEOLOGY LECTURE, PAGE 51
3. Important Paleozoic "Reptile" Groups
a. The Anapsids
- most primitive forms which are unquestionably reptilian; consists of small lizard-like
"parareptiles" (such as the captorhinids and procolophonids) and the large Permian-age knobbyskulled herbivorous pareiasaurs
b. Mesosaurs
- aquatic parareptiles of Permian age from Africa and South America; probably restricted to one
limited ocean basin and was used as evidence of continental drift
- up to one meter long, slender; with long, laterally-compressed tail and neck and paddle-like
feet; the marginal teeth were long and slender (for straining microplankton?)
c. Synapsids
- early synapsids had a single, lower lateral temporal opening
- they have often been termed "mammal-like reptiles", but synapsids are now typically considered
to be a group distinct from "true reptiles"; the Synapsida often includes pelycosaurs, therapsids,
and true mammals
c1. Pelycosaurs
- Pennsylvanian-Permian synapsids
- important Paleozoic groups include the Sphenacodonts (highly predaceous forms such as
Dimetrodon; many with elongate neural spines forming "sails"), and the Edaphosaurs
(herbivores; usually with elongate neural spines with crossbars)
c2. Therapsids
- therapsid jaw structure was improved over the pelycosaurs, with reduction of canine teeth to
one per jaw half; the skeleton had improved locomotion versus earlier "reptiles"
- Therapsids include the Dinocephalians (very large Permian carnivores and herbivores);
Anomodonts (Permian to Triassic; herbivorous; most successful mammal-like reptiles; include
the tusked dicynodonts); Cynodonts (Permian to Jurassic; advanced mammal-like reptiles
representing transitional stages in the development of mammalian characteristics)
P. The Late Paleozoic (Permian) Extinction Events
1. The Middle Permian (Guadalupian) Extinction Event
- at about 7 to 8 million years before the end of the Permian, a mass extinction killed about 70
percent of all marine species
- the reef communities were destroyed, and three-fourths of the genera of fusulinid
foraminiferans became extinct
- sedimentary evidence indicates that anoxic (oxygen-poor) waters from the Permian "stratified
seas" began to ascend upon the Middle Permian marine shelves, with devastating results
2. The End-Permian Extinction Event
- this was the greatest Phanerozoic extinction event, with some 80 to 85 percent of all species
HISTORICAL GEOLOGY LECTURE, PAGE 52
becoming extinct
- all of the tabulate corals and trilobites became extinct, and only a few ammonoids, crinoids and
bryozoans survived the extinction event
- terrestrial forests were replaced by patches of small, non-woody lycopods; the huge numbers of
fungal remains in shallow marine environments indicate that fungi flourished due to the death
and decay of the forests
- the End-Permian extinction was the first major extinction of terrestrial animals, with most
families of therapsids becoming extinct
- Permian extinctions may have been caused by upwelling anoxic waters onto the continental
shelves (such as in the Guadalupian Event), by stratification of the Permian Seas (which would
lead to stagnation of deep-ocean waters, as well as to dramatic warming and drying of climates),
by the formation of Pangaea (which led to less marine shelf area for organisms, and more aridity
in the continental interiors), or from volcanism [huge volcanic deposits in China match the date
of the Guadalupian Event; the "Siberian Traps" of northeast Asia match the date of the EndPermian Event; carbon dioxide from the volcanism caused by this single, moving mantle
plume/hotspot would increase global warming and may have triggered the melting of methane
hydrates on the ocean floor, with an enhanced greenhouse effect)
XIV. Mesozoic Plate Tectonics and Paleogeography
A. Early Triassic
- all land masses become united as the supercontinent Pangaea
- sea level rose slightly, but most landmasses were above sealevel
- during the Early and Middle Triassic, erosion subdued the Appalachian Mountains (which were
located near the center of Pangaea)
B. Late Triassic - Jurassic
1. The Breakup of Pangaea
- the Tethys Seaway (situated around the paleoequator in the Mediterranean region) began to
lengthen due to rifting between southern Europe and Africa; this rifting spread westward to
ultimately separate North and South America
- North America began to rift from Africa in the Middle Jurassic, forming a series of triple
junctions
- the Atlantic Ocean began to form, dividing Pangaea into a series of basins throughout eastern
North America (the Newark Supergroup); these rift basins contained a series of large lakes and
with mafic magmas intruding the fault block basins (basaltic sills from the Palisades, along the
Hudson River near New York City, represent a part of this rift system)
2. Formation of the Gulf of Mexico
- the Gulf of Mexico began forming during the Middle and Late Jurassic; the initial rifting
formed an evaporite basin within which great thicknesses of evaporites (Ex. = Louann Salt, Gulf
Coast of Texas) were precipitated; because of their low density, these salts have moved up
through younger-aged sediments as salt domes (diapirs), which are associated with the great
HISTORICAL GEOLOGY LECTURE, PAGE 53
petroleum reservoirs and sulfur deposits of the Gulf Coast
3. Jurassic Paleogeography
- there was a general rise in sealevel through the Middle and Late Jurassic
- there was a southern, tropical province (the Tethyan Realm; with warm-adapted molluscs, coral
reefs, and with the production of carbonates) and the Boreal Realm (to the north, with cooleradapted species)
4. Tectonism in Western North America
a. Paleozoic - Triassic Tectonism and Sedimentation
- after the Late Paleozoic Antler Orogeny, the Golconda Arc sutured onto the Pacific coast of
North America (the Sonoma Orogeny), adding a series of terranes (Sonomia) in the region of
southeastern Oregon and northern California and Nevada
- in Middle Triassic time a subduction zone extended from Alaska to Chile, creating a series of
Andes-type mountains; subduction of the oceanic plate beneath North America created extensive
intrusions (such as the Jurassic-age intrusives of the Sierra Nevada range of California); the
subduction zone is indicated by deposition of the Franciscan Sequence of California (consisting
of a series of turbidite deposits and accretionary wedges); this tectonic event is termed the
Nevadan Orogeny
- western North America had primarily non-marine deposition through most of the Triassic;
climate was primarily arid, although at certain times there was enough moisture for the growth of
large forests (an example is at Petrified Forest in Arizona, with the spectacular "Painted Desert"
redbeds representing ancient soil zones deposited in seasonally wet-dry climates)
b. Jurassic Tectonism and Sedimentation
- during the Jurassic a large exotic terrane (consisting of a composite block of several smaller
terranes) collided in the region of Washington to southern Alaska, substantially adding to the
northwestern North American Craton
- sealevel rose in a series of four transgressions in the Middle and Late Jurassic, eventually
forming the Sundance Sea (centered around Wyoming, and extending into the surrounding
states); this marine basin was created because the eastward thrusting and folding due to west
coast tectonism formed a large foreland basin
- great volumes of sediment were shed from the fold-and-thrust belt towards the east, eventually
filling in much of the Sundance Sea by Late Jurassic times; this created a series of river, lake and
swamp deposits representing the Morrison Formation (famous for the presence of large
dinosaurs, such as at Dinosaur National Monument in Utah)
- during the Jurassic a couple of periods of aridity are indicated, represented by ancient sand dune
deposits of the Wingate Sandstone and Navajo Sandstone
C. Cretaceous Tectonism and Paleoclimate
1. Plate Tectonics
- by Late Cretaceous time, Gondwanaland rifted to form South America, Africa and India
HISTORICAL GEOLOGY LECTURE, PAGE 54
(Antarctica and Australia remained connected to one another); the separation of continents
caused the oceans to widen
2. Cretaceous Ocean Circulation and Sedimentation
- global sealevel rose due to the expansion of the total volume of mid-oceanic ridges and mantle
plumes (sealevel was as high as any time during the Phanerozoic, depositing large volumes of
sediment on the continental cratons - in North America this is termed the Zuni Sequence)
- the Tethys Seaway was a dominant feature of the Cretaceous, along which were prominent
carbonate banks and rudist bivalve reefs
- during the Middle Cretaceous anoxic waters accumulated within deeper ocean waters
(indicating poor vertical circulation within the warm seas); this resulted in accumulation of
organic-rich muds to form black shales
- warm temperatures spread to higher latitudes by Middle Cretaceous time (as indicated by the
presence of fossils of warm-adapted plants in northern Alaska, Greenland and Antarctica;
dinosaurs lived within about 15 degrees of the Cretaceous South Pole); this is possibly due to
upwelling of hypersaline warm waters around the poles
- oxygen isotope data indicates a decline in oceanic temperatures during the Late Cretaceous;
ocean circulation changed, wherein cool, high-latitude waters sank into the deep ocean (the
Global Conveyer Belt Model), bringing oxygen with them (and therefore with a decline in the
amount of black shales seen in latest Cretaceous marine deposits); reef-forming rudist bivalves
became extinct
XV. Mesozoic Life
A. Marine Invertebrates
1. Triassic-Jurassic Marine Invertebrates
a. Benthos
- molluscs (bivalves, gastropods), sea urchins and scleractinian corals (hexacorals) become
abundant
- by latest Triassic and Early Jurassic time hexacorals form large reefs
b. Phytoplankton
- microscopic photosynthetic "plants" floating near the Ocean's surface became very important
- include dinoflagellates and coccolith "algae" (calcareous nannoplankton), which are autotrophic
organisms that formed the base of the food chain
c. Large Nektonic Predators
- especially cephalopods such as ammonites (with coiled shells, that constitute important index
fossils throughout the Permian and Mesozoic) and the cigar-shaped squid-like belemnites
d. Two periods of extinction occurred during the Triassic
- dinosaurs became the dominant reptile group after the first, or "end-Carnian Extinction Event"
HISTORICAL GEOLOGY LECTURE, PAGE 55
during the Upper Triassic
- about half of all marine animals became extinct during the End-Triassic extinction event (all of
the conodonts and the placodont reptiles became extinct, and most species of bivalves,
ammonoids, plesiosaurs and icthyosaurs became extinct)
- on land, most species of seed plants became extinct (the ferns briefly underwent an abrupt
expansion at this time)
- almost all of the therapsids became extinct; dinosaurs survived the extinction event, and
underwent an adaptive radiation in the Jurassic
- the extinction was probably due to a sudden period of greenhouse warming at the
Triassic/Jurassic boundary, probably due to the intense volcanism associated with the breakup of
Pangaea
2. Cretaceous Invertebrates
- there was a combination of "modern" and "ancient" forms
a. Plankton
- "modern" dinoflagellates, diatoms; coccoliths (calcareous nannoplankton) and planktonic
foraminiferans form extensive chalks (Exs. = Austin Chalk of Texas; Chalk Cliffs of Dover,
England)
b. Nekton
- ammonoids are very important index fossils; many forms had complex suture patterns and with
a great diversity of shell morphology
c. Benthos
- "modern" groups of foraminiferans, bryozoans, bivalves, gastropods, crabs; rudist bivalves
dominate reef environments; brachiopods and stalked crinoids decline
B. Marine Vertebrates
1. Mesozoic Fishes
a. Teleost Ray-Finned Fishes
- ray-finned fish develop better jaws and evolve swim bladders; Teleost ray-finned fish first
appear during the Late Mesozoic (these "modern" fish have symmetrical tails, round and thin
scales, specialized paired fins, and short jaws that can open wide and fast for "suction feeding")
b. Chondrichthyans
- sharks (especially the shell-crushing hybodonts) are abundant
2. Marine Reptiles become Top Predators
a. Turtles
- develop shells; most vertebrae and ribs are fused to shell; limbs and limb girdles modified for
HISTORICAL GEOLOGY LECTURE, PAGE 56
sprawling posture
- anapsid skull; teeth rudimentary or absent
- during the Cretaceous marine turtles grew to huge proportions
b. Ichthyosaurs
- Dolphin-, tuna- and shark-like neodiapsid reptiles of the Mesozoic
- skull highly modified for aquatic life, with a euryapsid skull pattern
- tendency through time to develop a hypocercal tail (with the vertebral column bending into the
lower lobe of the tail fin); limbs reduced to steering paddles
- reproduction probably took place in water and with live birth (some females have skeletons of
young ichthyosaurs inside them)
c. Sauropterygians
- lepidosauromorph neodiapsids that include the nothosaurs, pachypleurosaurs, plesiosaurs, and
possibly the placodonts; aquatic reptiles with euryapsid temporal openings
- Nothosaurs (Triassic; the limbs of nothosaurs were relatively normal) and Plesiosaurs (JurassicCretaceous; plesiosaurs developed paddles by adding toe joints; their nostrils migrated far back
on the skull; the ventral ribs formed a basket-like structure; the ventral portion of the limb girdles
were expanded into plate-like structures)
- Placodonts were wierd Triassic, aquatic mollusc-eating neodiapsids (but with euryapsid
temporal opening); most with "pavement teeth"; placodonts were kin to the "Sauroptergyia" and
are now often placed within that group
d. Crocodilians
- crocodiles, alligators and their relatives; belong to the archosaurs (see discussion below)
- Skull elongate, flattened, massive; evolutionary trend in posterior extension of the palatal bones
to form a secondary palate (for aquatic mode of life or to support the elongate snout?)
- with dermal armor; with a semi-improved gait [hind legs longer than front legs; improved
ankle joint]
- some Mesozoic crocodilians were fully marine in their habits
C. Important Land Plants of the Mesozoic
1. "Gymnosperms"
a. Conifers
- include pines, spruces, firs, hemlocks, junipers, cypresses, redwoods; Triassic-Recent
- woody trees and shrubs with needlelike or scalelike leaves; most are evergreens (shed leaves
throughout year but retain enough of them to distinguish them from deciduous trees); conifers
have Cones (cone-shaped clusters of modified leaves that house the reproductive organs); seeds
develop on the shelf-like scales of the female cones
b. Cycads and Cycadeoids
HISTORICAL GEOLOGY LECTURE, PAGE 57
- cycads (Permian-Recent) and cycadeoids (Triassic-Cretaceous) are often difficult to distinguish
as fossils (both often form shrubby or tree-like plants with pinnate, strap-like, palm-like leaves
and similar wood)
2. Angiosperms
- flowering plants (Triassic??; Cretaceous- Recent); include the majority of recent plants
- with pollen-producing flowers (flowers developed from modified leaves); the wind-carried or
insect-borne pollen lands on the stigma (the end portion of the female element); the pollen tube
grows to the ovules for the transport of sperm; one portion of the sperm fertilizes the egg and
another portion unites with a second portion of the ovule (which generally forms a structure
which provides nutrients for the growing embryo; this is termed "double fertilization"); a seed
develops that is totally encased inside a fruit
- angiosperms became the dominant land plants in the Late Cretaceous (they are rapid colonizers)
D. "Lissamphibians" Evolve in the Mesozoic
- include frogs and toads (Triassic-Recent), the long-bodied aquatic salamanders (JurassicRecent) and the worm-like caecilians (Jurassic-Recent)
Frogs and Toads - greatly derived (most features are related to jumping): only 5 to 9 trunk
vertebrae; no ribs; pelvis modified for jumping; long legs with arm and lower leg bones fused;
skull forms "open" structure
E. Diapsids become the Dominant Land Vertebrates
- diapsids have two temporal openings; includes all modern reptile groups except turtles; also
include dinosaurs, pterosaurs, plesiosaurs and several other ancient groups
1. Lepidosauromorphs
- include sphenodontids, lizards, snakes, and the extinct aquatic placodonts, nothosaurs, and
plesiosaurs
- differentiated from archosauromorphs by retention of sprawling posture
- Sphenodontids, represented today by the Tuatara from New Zealand, were very common small
lizard-like reptiles during the Triassic and Jurassic
- Lizards (Triassic - Recent) have a tendency towards streptostyly (loosening of the skull to eat
larger prey)
- Cretaceous marine lizards, especially the mosasaurs, became very important large predators in
the oceans
Snakes (Upper Cretaceous - Recent) have extreme streptostyly, their ancestors lost their limbs
during the Cretaceous
2. Primitive Archosauromorphs
- most important structure uniting archosauromorphs is ankle and foot structure (related to
upright posture)
HISTORICAL GEOLOGY LECTURE, PAGE 58
Most Important Groups of Primitive Archosauromorphs are:
a. Trilophosaurids
- small to medium-sized, Triassic-age, lizard-like "herbivorous" reptiles (teeth typically with
three cusps); postcranial skeleton like primitive archosaurs; Ex. = Trilophosaurus
b. Rhynchosaurs
- heavily-built Triassic herbivorous lepidosaurians; advanced types with upper jaw with broad
crushing toothplates and a parrot-like toothless beak
2. Archosaurs
- the "ruling reptiles" including the dinosaurs, crocodiles, pterosaurs and many primitive groups
(the thecodonts)
- Skull with diapsid condition (two temporal openings) and may evolve one or more other skull
openings; there is a thecodont dentition (the teeth are placed in sockets)
- skeleton with hind limb much better developed than the forelimb; tendency towards bipedal
pose involves change in hip and femur (“thighbone”) structure
Important Early Mesozoic Archosaurs Include:
a. Rauisuchians ("Poposaurs")
- large, fierce Middle and Upper Triassic carnivorous archosaurs (up to 6 meters long) with huge
carnivorous dinosaur-like skulls
b. Aetosaurs
- relatively large herbivorous quadrupeds of Late Triassic age; body covered by armor plates
c. Phytosaurs
- very abundant, crocodile-like, Upper Triassic thecodonts
3. Dinosaurs
- dinosaurs originated in the Middle Triassic and became extinct at the end of the Cretaceous
- Over 800 species of dinosaurs are known
- limbs brought under the body and moved in a fore-and-aft direction [femur inturned; the pelvis
"socket" (acetabulum) is wide-open (perforate); improved ankle joint; digits form the main
surface that contacts the ground (digitigrade posture)]
- dinosaurs became the dominant reptile group after the "end-Carnian Extinction Event" during
the Upper Triassic, which cleared ecospace for the dinosaurs to take over
Types of Dinosaurs Include:
a. Saurischians
- with a primitive "triradiate" pelvis structure; digits of hand and foot reduced; teeth occupied the
rims of the jaws; large openings reduced the weight of the skull
HISTORICAL GEOLOGY LECTURE, PAGE 59
- saurischians dominated during the early Mesozoic but were outnumbered by the ornithischians
during the upper Mesozoic
- The most Important Saurischians are:
a1. Theropods
- include all of the bipedal carnivorous dinosaurs (Late Triassic - Cretaceous)
- neck is generally short; lower portion of hind limb is longer than the upper part; hands bear
sharp claws and there are two or three fingers only; feet with three clawed toes (the fifth is
always reduced and the first or big toe is shortened and turned backwards)
- include many groups such as the Ceratosaurs, Carnosaurs (spinosaurs and allosaurs),
Coelurosaurs (including the ornithomimid "ostrich dinosaurs"), tyrannosaurids, and
deinonychosaurs ("raptors")]
a2. Sauropodomorphs
- typically heavily built quadrupedal dinosaurs with small heads and long necks; most with
peglike teeth; Upper Triassic-Upper Cretaceous
- "Prosauropods" - small- to large-sized; possible ancestors of sauropods; carnivorous,
herbivorous and perhaps omnivorous forms
- Sauropods were huge Jurassic/Cretaceous herbivores with quadrupedal pose, powerful limbs,
long tail, long neck and small head; the jaws were short and weak with small peglike or
spoonshaped teeth; the front legs were shorter than the hind legs; include the largest land animals
of all time (the Brachiosaurs)
b. Ornithischians
- pubis points backward (bird-hipped); with single median bone at the tip of the lower jaw (the
predentary); jaw with beak, posterior to which is a grinding dention; most with concave cheek
region (therefore most with muscular cheeks); tendency for internal nostrils to be displaced
posteriorly
The Groups of Ornithischians are:
b1. Ornithopods
- had bird-like feet with blunt claws or hooves; examples include the Hypsilophodontids,
Iguanodontids (Cretaceous) and Hadrosaurids ("duck-billed" dinosaurs)
b2. Pachycephalosaurs
- small group of Late Cretaceous "bone-headed" dinosaurs (with unusually thick skull roofs,
probably used for "butting contests" between males)
b3. Ceratopsians
- small to large dinosaurs with skulls ranging from relatively large to gigantic, often with horns
and large shields of bone; snout beaklike; almost exclusively quadrupedal; one of the last
HISTORICAL GEOLOGY LECTURE, PAGE 60
evolved (Cretaceous) and most abundant groups of dinosaurs
b4. Stegosaurs
- Jurassic-Cretaceous armored quadrupedal ornithischians
- relatively large; with small skull, front legs short; back arched high over long hind limbs; with
series of plates and spines arranged in a row down the neck, trunk and tail
b5. Ankylosaurs
- Jurassic-Cretaceous stocky dinosaurs with short, broad feet; with extensive development of
bony, armored carapace, often with tail club
4. Were Dinosaurs Warm-Blooded?
- Evidence cited that dinosaurs were endotherms includes the following:
a. Erect posture
- limbs held vertically (with metabolism like birds and mammals)
b. Bone structure
- dinosaurs have haversian canal systems in their bones like those of mammals (indicates more
rapid metabolic processes; but these seem to be present in large animals in general and are absent
in small animals)
- but dinosaurs did not have determinant growth and continued to increase in size throughout life
(unlike birds and mammals)
c. Population Studies/ Community Structure
- carnivorous dinosaur numbers (versus herbivores) are more like that of mammals than reptiles
d. Long-necked dinosaurs would have to have a more efficient heart in order to pump blood up
to their brains
e. A few dinosaurs were at least as intelligent as birds
f. Dinosaurs show social behavior (such as herding and "nurseries") that is unknown among
other reptiles
g. Dinosaurs have been discovered in Mesozoic "polar regions"
h. Some dinosaur fossils have feathers
i. Growth Rates
- reptiles grow slowly, dinosaurs grew quickly like birds and mammals
j. Oxygen Isotopes
- ratios are influenced by temperature; oxygen isotopes from dinosaur bones indicate more
HISTORICAL GEOLOGY LECTURE, PAGE 61
similarity to modern endotherms (warm-blooded animals) than ectotherms (cold-blooded
animals)
However, dinosaurs would probably maintain a relatively constant internal temperature due to
their small surface area versus volume. Also, if dinosaurs were such great endotherms why all of
the plates, frills, spikes and nasal cavities that probably served as heat exchangers, helping to
warm and cool their bodies?
5. Pterosaurs
- active flying diapsid reptiles from the Upper Triassic through Upper Cretaceous
- most from shallow marine environments
- Active Flight in pterosaurs is indicated by their hollow bones, keeled sternum (breastbone) for
attachment of flight muscles, the shoulder girdle and upper wing bone are modified to form a
pulley-like structure; the first three fingers are short, and the fourth finger is greatly elongate to
support the wing membrane, the fifth finger is absent
- the earliest pterosaurs, the rhamphorynchoids, had a long tail
- the pterodactyloids lost the tail, many had bony extensions at the back of their skulls, and
several types were of enormous proportions (Quetzalcoatlus, from the Big Bend region of Texas,
had a 40 foot wingspan)
F. Birds
1. Characteristics
- highest metabolic rate of any modern vertebrate
- bones are pneumatic (with extensive air-sac system for respiration); compact skeleton with
wing and leg bones reduced in number and many elements fused [including hand, foot, sacral
vertebrae, tail vertebrae, and clavicles (the "wishbone"); the sternum ("breast bone") has a large
keel that provides a broad base for the flight muscles
- skull bones are typically fused; modern birds are toothless with the beak covered by a horny bill
2. Origin of flight
a. Arboreal theory
- four-footed, ground-dwelling reptile became bipedal, then climbing, then began leaping from
tree to tree. Later it began parachuting, gliding and finally included active, powered flight
(probably the most popular theory for flight origins)
b. Cursorial theory
- feathers developed as thermoregulatory devices for insulation; then used for trapping insects;
then provided lift during running and leaping; then flight
3. Important Groups of Mesozoic Birds
a. Archaeopterygids
- includes Archaeopteryx, the earliest known undisputed bird (pigeon-size), from the Upper
HISTORICAL GEOLOGY LECTURE, PAGE 62
Jurassic
- there are no unique features in the bony skeleton to differentiate them from dinosaurs
- the skull of Archaeopteryx is birdlike, but with thecodont teeth; tail dinosaur-like; hind legs
and pelvis similar to saurischian dinosaurs; clavicles joined to form a bird-like furcula
("wishbone") but no keeled sternum
b.Hesperornithiformes
- loon-like aquatic, flightless, toothed Cretaceous birds
G. Mammals
1. Characteristics
a. Soft Anatomy
- have hair and specialized mammary glands for suckling their young
- different reproductive modes distinguish the major groups of living mammals [platypus and
echidnas are egg-laying monotremes; marsupials have a marsupium (a pouch in which most
embryonic development takes place); placentals have development taking place in the uterus and
the embryo is nourished by tissues of the placenta (the tissues shed following a birth)
- mammals are intelligent with complex behavioral patterns
- mammals are endothermic ("warm-blooded) and usually have high metabolic rates
b. Bones and Teeth
- the skeleton of mammals is modified for upright posture
- the most widely accepted paleontological definition of a mammal is articulation of the dentary
(jaw bone) with the squamosal of the skull (reptiles with articular-quadrate articulation)
- the articular and quadrate were modified in mammals to form two of their three earbones!
- molar teeth are often useful for identifying fossil mammals
2. Mesozoic Mammals
- mammals originated in the Late Triassic
- nearly all early mammals were very small
Some of the Most Important Mesozoic Mammals Groups were:
a. Triconodonts and Symmetrodonts
- Late Triassic to Late Cretaceous small mammals with multicuped molar teeth
b. Multituberculates
- multituberculates (Jurassic-Oligocene) were the most diverse and numerous Mesozoic
mammals
- they were rodent-like; they had a pair of large incisors, and with low, many-cusped molar teeth
c. Marsupials
- Late Cretaceous to Recent
HISTORICAL GEOLOGY LECTURE, PAGE 63
- the didelphid marsupials were the most primitive marsupials and probably ancestral to other
types; they include the American oppossum
d. Placentals
- the oldest undisputed eutherian is a well-preserved shrew-sized placental from the Early
Cretaceous of Mongolia, which proves that there were true placental mammals by this time
H. The End-Mesozoic Extinction Event
- several groups (including dinosaurs and ammonites) became extinct at the end of the
Cretaceous (Cretaceous/Tertiary, K/T, or Maastrichtian/Danian Boundary; approximately 65 Ma)
1. Catastrophic Theories
a. Extraterrestrial Causes
- large asteroid (10 to 20 kilometers across) hit the earth, creating a cloud of dust and something
similar to "nuclear winter"; decrease in photosynthesis, increase in carbon dioxide, increase in
acidity of oceans and a short-term "greenhouse effect"?
- evidence includes the iridium layer at the Cretaceous/Tertiary boundary (probably deposited
over a period no more than a few thousand years), the presence of glassy spherules (tektites),
microscopic diamonds, and "tsunami beds" at the K/T boundary
- the impact structure may be represented by the Chicxulub Crater, on the Yucatan Peninsula in
Mexico
- possible conflicting data concerns the apparent extinction of most dinosaurs prior to the K/T
boundary
b. Vulcanology models
- geochemical data in boundary rocks indicate major volcanic eruptions (e.g., The Deccan Traps
of India) at the end of the Cretaceous
- volcanic eruptions would produce greenhouse gases that would trigger rapid climate change
b. Hypothesis of Gradual Change
- the stratified ocean of the Middle Cretaceous gave way to more modern ocean circulation (the
"Global Conveyer Belt Model), which brought colder waters to the tropics and changed climate
- the end of the Cretaceous is marked by a major regression and drying up of epicontinental seas
- tectonic activity and mountain building led to a major change in climate and seasonality
- Western North America may have seen a gradual decrease in temperature between the late
Cretaceous and Paleocene of 10°C ; evidence includes gradual extinction and replacement of
dinosaurs and other groups (including plesiosaurs, pterosaurs, ostracods, bryozoans, ammonites
and bivalves, all with low diversity at the end of the Cretaceous)
XVI. The Cenozoic Era
A. Paleogene Plate Tectonics and Climate
HISTORICAL GEOLOGY LECTURE, PAGE 64
1. General Plate Configurations and Climate
a. Paleocene
- during the Early Paleogene, continents were arranged much like today but were bunched closer
together
- average global temperature increased dramatically within the late Paleocene (probably due to
global warming and the melting of frozen methane hydrates along the continental slopes); this led
to a shift in marine and terrestrial faunas
b. Eocene Plate Tectonics and Climate
b1. Early Eocene
- during the Early Eocene climates were warm (with tropical floras and faunas in England and
even extending well within the Arctic Circle!); this warming may have been due to large
amounts of water vapor in the air (water vapor is a greenhouse gas)
b2. Late Eocene
- by late Eocene times climate was cooler and drier, with expansion of glaciers over Antarctica
by the Eocene-Oligocene transition; Australia separated from Antarctica and forms the cold
circumpolar current; the psychrosphere formed (deep, cold ocean currents) and climate
deteriorated (colder and/or drier)
2. Paleogeography and Sedimentation in the Gulf of Mexico and Atlantic Coast
a. Gulf of Mexico
- during Paleogene time, marine waters still occupied the Mississippi Embayment (an inland
extension of the Gulf of Mexico), where thick Paleocene-Eocene sediment sequences
accumulated; there was a regression of waters in the Oligocene, followed by a brief Oligocene
transgression
b. Bolide Impacts in the Atlantic
- in the Chesapeake Bay region of the middle Atlantic coast of the U. S., a 3 to 5 kilometer wide
asteroid struck the Earth (as indicated by the remains of a huge impact structure, and by shocked
quartz); other equivalent structures are found in the Atlantic east of New Jersey, which indicates
that a multiple bolide impact occurred about 36 Ma during the Late Eocene; tsunami ("tidal
wave") deposits from this impact are present from New Jersey to North Carolina
3. Paleogene Tectonism in the Western United States
- in latest Cretaceous through Paleogene time a region of fold-and-thrust belts and uplifts (the
Laramide Orogeny) extended from Mexico, West Texas, and northward into Canada; large
blocks of Precambrian-age rocks were uplifted, the largest of these centered around Colorado
(forming the Ancestral Rocky Mountains); the Laramide Orogeny may have been due to a lowangle subduction zone, melting and sending magma into the overlying crust and creating a series
of uplifts and basins
HISTORICAL GEOLOGY LECTURE, PAGE 65
- the formation of basins and uplifts is reflected in the formation of giant lake basins represented
by the Green River Formation (Eocene) of Utah, Colorado and Wyoming, by hot-spot volcanism
in the Absaroka Mountains (where Yellowstone National Park is situated; the burial of fossil
forests in Yellowstone by volcanic tuffs is a result of this activity), and by the uplift of the Black
Hills of South Dakota
B. Neogene Plate Tectonics and Climate
1. Ocean Circulation and Climates Change
a. Formation of Cold Ocean Circulation
- Miocene-age ice-rafted boulders from Antarctica indicates the expansion of continental glaciers
onto the Antarctic continental shelves; this is due to the deepening and widening of the Antarctic
Circumpolar Current with the continued movement of Australia away from Antarctica
- Greenland/northern Europe rifting opened the Arctic Ocean (this helped form the
psychrosphere)
b. Warming during the Early Pliocene
- Early Pliocene climates (approx. 5 Ma) were relatively warm, sea levels rose, and marine
deposits are found inland in North America and countries bordering the North Sea and
Mediterranean
c. Beginning of the Ice Ages
- at approximately 3.2 Ma the modern Ice Age began; details of the timing and geographic
distribution of continental glaciation is indicated by erratic boulders (deposited far from their
point of origin), by ice-deposited glacial till (Tillites), by isostatic depression of the land due to
glacial weight, by glacial scouring, by lowering of sea level (at the glacial maxium sea level was
approximately 100 meters lower than today, or about 330 feet), and by distribution (and
migration) of plant and animal species
- oxygen isotope ratios indicate that by 2.5 Ma the Northern Hemisphere had moved fully into the
Ice Age; many regions became drier as cooler seas released less water vapor into the atmosphere
2. Formation of the Caribbean Sea and Isthmus of Panama
a. Caribbean Sea
- during the Cretaceous the Caribbean was a small segment of the Pacific Plate that was pushing
toward the Atlantic; during the Cenozoic it became a distinct plate due to a new subduction zone
appearing along the west coast of Central America
b. Isthmus of Panama
- the Isthmus of Panama was emplaced by plate movements between 3.5 to 3 Ma, at about the
time the Ice Age in the Northern Hemisphere began
HISTORICAL GEOLOGY LECTURE, PAGE 66
3. Plate Tectonics in Eurasia and Africa
- a series of mountain chains stretching from Spain and North Africa to southeast Asia were
created due to remnants of Gondwanaland moving northward into Eurasia
- the Alps and other Cenozoic mountains of the Mediterranean region were created when the
African Plate moved northward into the Eurasian Plate
- India was an island continent that split from Antarctica during the Cretaceous (about 80 Ma); it
moved northward and began to wedge beneath the southern margin of Tibet about 20 Ma; a
couple of huge thrust faults were created, with even greater crustal wedging and thickening; these
underthrust slices of crust built the Himalayas into the World's tallest mountain chain (about 5.5
miles high)
- the collision of the African Plate with India and Eurasia destroyed the remnants of the Tethys
Seaway; during the Miocene the Mediterranean shrank, forming a huge evaporite basin (with
deposition of large amounts of salt); at about 5 Ma the natural barrier at Gibralter was breached,
refilling the Mediterranean with Atlantic seawater
4. Circum-Pacific Orogenies
- plate subduction in the circum-Pacific Belt gives rise to orogenies in the Philippines, Japan, the
Aleutian Islands, and North, Central and South America
5. Development of Modern Physiographic Provinces in the Western United States:
a. Rocky Mountains
- during the Oliogocene, most of the Laramide Uplifts had been leveled, depositing a veneer of
sediments around them (an example are the terrestrial deposits of the Badlands of South Dakota,
which yields a spectacular fossil mammal fauna)
- Uplift of the Rockies began during the Early Miocene, and accelerated about 5 Ma; total uplift
is 1 to 2 miles; sediments from the uplifting rockies spread eastward during the Late Miocene,
resulting in the deposition of the Ogallala Formation (abundant caliche nodules in ancient
Ogallala soils indicates seasonally arid climates; the buried Ogallala Formation forms the famous
and very important Ogallala Aquifer, the major source of groundwater on the High Plains)
b. Colorado Plateau
- situated in the "Four Corners" of New Mexico, Colorado, Utah and Arizona; relatively flatlying strata that has been uplifted about 1 mile above sealevel; uplift began about 10 to 8 Ma,
with uplift accelerating about 5 Ma (at the same time as major uplifting occurred in the Rockies);
uplift of the Colorado Plateau was accompanied by downcutting of the Colorado River, creating
the Grand Canyon; swelling of the Earth's mantle and isostatic adjustment probably created the
modern Rockies and Colorado Plateau
c. Basin-and-Range Province
- centered around Nevada, forming the Great Basin; consists of fault block basins (Grabens)
separated by upfaulted blocks forming ridges (Horsts); crustal thickness is about 20-30
kilometers (versus about 35-50 kilometers in the Colorado Plateau), which indicates crustal
extension in the Basin-and-Range Province; this faulting began in the Early Miocene
HISTORICAL GEOLOGY LECTURE, PAGE 67
d. The Great Valley and Coast Ranges
- the Great Valley is an elongate basin in California situated between the Sierra Nevada Range
and the uplift area of the California Coast Ranges; faulting and deformation from the Pliocene
(about 5 Ma) to the present has moved coastal California northward by about 100 kms (60
Miles); uplift since the Pliocene converted the Central Valley from a marine basin to an
agriculturally-rich (and oil-rich) terrestrial basin; the Great Valley and Basin and Range
provinces were probably created by crustal shearing adjacent to the transform strike-slip faults of
the Pacific coast
e. Columbia Plateau and Snake River Plain
- centered in Oregon; consists of thick sequences of flood basalts created by the Yellowstone
Hotspot, which has shifted eastward through time
f. Cascade Ranges
- volcanic belt in the Pacific Northwest; subduction of the Pacific/Juan de Fuca plate beneath the
North American Plate created a series of volcanic mountains, most of which have formed within
the past 2 million years
6. Catastrophic Events at the End of the Ice Age
- a huge lake (Glacial Lake Missoula) was created in the northwestern United States by glacial
ice pushing down from Canada; when this ice dam broke sometime between 11 and 20Ka,
catastrophic flooding carved the landscape into the Channeled Scablands of the Pacific
Northwest, and with deposition of giant ripples to the west (this process repeated itself about 40
times during the Pleistocene)
XVII. Cenozoic Life
A. Marine Life
1. Marine Benthos
- groups surviving the Cretaceous extinction (benthic foraminifera, sea urchins, cheilostome
bryozoans, crabs, snails) had an adaptive radiation in the Paleogene
- there are few corals in the Paleocene and Eocene, but increasing Magnesium/Calcium ratios in
marine waters triggered the growth of large reefs during the Oligocene
2. Marine Plankton
- calcareous nannoplankton (coccoliths) and planktonic foraminifera almost became extinct at the
end of the Cretaceous, but the few species surviving experienced a very large adaptive radiation
during the Tertiary
- diatoms and dinoflagellates were not as greatly affected by K/T extinction, but also diversified
during the Cenozoic
3. Marine Nektonic Carnivores
- new types of sharks, whales, pinnipeds (seals, sea lions, walruses) and penguins evolved and
HISTORICAL GEOLOGY LECTURE, PAGE 68
diversified during the Paleogene
a. Sharks
- improvements in locomotion and jaw structure led to an adaptive radiation of modern shark
groups
- some Miocene sharks, which probably fed on the new gigantic whales, were of enormous
proportions
b.Whales
- mesonychids (the largest land mammal carnivores of all times), whales, artiodactyls (cattle,
antelopes, pigs, etc.) and perissodactyls (horses, rhinos and tapirs) are related and often placed
within the same "superorder"
- whales are specialized for aquatic life with a streamlined body; the tail forms a horizontal fluke
for propulsion; hind limb absent; fore limb forms a short flipper for steering; brains large and
complex; primarily carnivores (feed on squid, fish or plankton)
- the Archeocetes [earliest whales; Eocene - Oligocene, Miocene(?)] were derived from landdwelling mesonychids or artiodactyls; includes the long-snouted, toothed "zeuglodonts")
- the Odontocetes (Miocene - Present) are toothed whales, which includes dolphins, porpoises,
sperm and killer whales
- the Mysticetes (Miocene - Present) include the plankton-straining baleen whales; these are the
largest animals that ever lived
c. "Pinnipeds"
- seals, sealions and walruses are often lumped together, but genetic and paleontological studies
indicate that sealions and fur seals probably came from dog-like ancestors, whereas true seals
were probably derived from otter-like ancestors
B. Flowering Plants (Angiosperms) Become Dominant
1. Types of Angiosperms
a. Monocotyledons ("Monocots")
- include grasses, lilies, sedges, palms, pineapples and orchids; Jurassic(?); Cretaceous-Recent
- leaves usually parallel veined and usually with only one cotyledon (the "seed leaf" of the
embryo)
b. Dicotyledons ("Dicots")
- include herbs and woody plants, cacti, and water lilies; Cretaceous-Recent
- usually leaves are net veined and their embryos have two cotyledons ("seed leaves")
2. Changing Cenozoic Climates Lead to Changing Vegetation
a. Broad-leaved evergreen "gymnosperms" became extinct at the Cretaceous/Tertiary boundary,
to be replaced by deciduous dicots
HISTORICAL GEOLOGY LECTURE, PAGE 69
b. Paleocene to Early Eocene global climate became warmer and precipitation increased, with
expansion of tropical forests to about 50° to 60° North latitude
c. Upper Eocene with decline in temperature and drier climates, and with spread of broadleaf
deciduous forests
d. During Miocene with drier climates and development of widespread grasslands (grasses have
continuously-growing leaves and can withstand heavy grazing), and with adaptive radiation of
"weeds" (the Compositae, mostly annual or perennial herbs capable of rapid development and
colonizing disturbed habitats)
e. During the Pliocene the climate of northwestern Europe and North Africa changed
dramatically, with loss of subtropical forests in Europe (due to cooler temperatures), and the
spread of the Sahara Desert (due to increased aridity in North Africa)
C. The Adaptive Radiation of Birds
1. Flightless Birds
- If there is no continual selection for the maintenance of flight apparatus (as is the case on
islands or island continents), birds tend to become flightless
- bird groups that developed flightless members include the Gruiformes (cranes, rails, and the
giant phorusrhacids), Diatrymiformes and "Ratites" [include moas (New Zealand; some over
three meters tall), elephantbirds (up to 500 kilograms), ostriches, rheas, cassowaries, emus,
tinomous and kiwis]
2. The Passeriform Birds Flourish
- the most important group of birds are the Passerines (Order Passeriformes), or songbirds
- there are over 5000 modern species (three-fifths of all living birds), and are placed in from 50 to
70 families
- flowering plants, rodents and birds "co-evolved", with the evolution of angiosperms greatly
influencing the evolution of rodents and birds
D. Plate Tectonics and Changing Climates Influence the Types of Birds and Mammals on the
Continents
1. The Island Continents of South America and Australia Evolve Unique Animals
a. South America
- Phorusrhacids were giant flightless Early Tertiary carnivorous birds that were at the top of the
terrestrial food chain
- marsupials were very successful in South America during the Tertiary, including Didelphid
oppossums, mole-like and rodent-like marsupials, dog-like marsupials (the borhyaenids), and
even "sabre-toothed cat"-like marsupials (the thylacosmilids)
- "Edentates" were also important within South America, including giant armadillos and the
Volkswagen-sized armadillo-like glyptodonts, and giant ground sloths (some as large as
HISTORICAL GEOLOGY LECTURE, PAGE 70
elephants)
- beginning in the Oligocene, there was a unique radiation of placental herbivores in South
America including the Litopterns (with rabbit-like groups, the horse-like Prototheriids, and the
weird camel-like, trunk-bearing Macraucheniids) and the Notoungulates (with rodent-like
species, the rhino-like toxodonts and astrapotheres, and the tapir-like pyrotheres)
- the "Great Faunal Interchange" occurred during the Pliocene-Pleistocene with faunas migrating
north and south across Central America; all of the large marsupial carnivores and odd placental
herbivores in South American became extinct
b. Australia
- several "ratite" bird groups evolved in Australia including the cassowaries, emus and the extinct
dromornithids (the largest dromornithid was 3 meters high and weighed about 500 kilograms!)
- marsupials dominated the faunas in Australia with oppossum-like groups, carnivorous
marsupials (like the Tasmanian Devil, the dog-like Thylacine, and the lion-like thylacoleonids),
mole-like and rodent-like groups, and a wide variety of large herbivores (including kangaroos
and the rhino-sized diprotodontids)
3. The Placental (Eutherian) Mammals Radiate
a. Rodents
- rodents include squirrels, rats, mice and guinea pigs
- the skull and teeth are much modified for gnawing; with one pair of continuously-growing
incisor teeth
- rodents include approximately 40% of all known modern mammalian species (over 2,000 living
species); approximately 50 families evolved in the Cenozoic
b. Carnivorous Mammals
b1. "Creodonts" ("Order Creodonta")
- probably polyphyletic, but some members were ancestral to the "true carnivores"
- dominant Tertiary carnivores; found on all continents except Australia and South America
b2. "True Carnivores" (Order Carnivora)
- true carnivores were a relatively minor part of faunas in the Paleocene and early Eocene; during
the Middle Eocene cat-like and dog-like lineages evolved, which became very successful groups
of predators
c. Early Rooters and Browsers
- the earliest herbivores lived mostly during the Paleocene and Eocene; they were from rabbit- to
elephant-sized; probably most were rooters or feeders on tubers (with clawed feet, large canines
and broad, low crowned cheek teeth; they typically had a complete dentition with no diastema)
- includes the pig-like Taeniodonts, semiaquatic Pantodonts, massive herbivorous Dinocerata
(the "Uintatheres"), the large clawed-footed Tillodonts, the rhino-sized Embrithopods, and the
"Condylarths" (ancestral to all other herbivorous groups)
HISTORICAL GEOLOGY LECTURE, PAGE 71
d. The Elephants (Proboscideans)
- Eocene - Recent; elephants are "Tethytheres" [and are kin to the rodent-like hyraxes and the
marine dugongs and manatees (Sirenians)]
- overall evolutionary trends in elephants include increase in size, enlarged cheek teeth,
enlargement of the second incisor teeth to form tusks, and development of a proboscis (the
elephant "trunk"; with the nasal opening in the skull becoming posteriorly-placed)
- the most important groups of proboscideans are the Deinotheres (with downturned and
backwardly curved tusks), the Gomphotheres ("shovel-tuskers") and the Elephantidae ("true"
elephants and mammoths)]
e. Perissodactyls
- "odd toed" ungulates including tapirs, rhinoceroses, horses, brontotheres and chalicotheres
- derived from condylarths; first appear in the Eocene (also peaked in the Eocene); good fossil
record in North America and Eurasia and later members are found in Africa and South America
- the axis of weight-bearing in the leg passes through the middle or third digit; most members are
three-toed but later horses eliminated the lateral digits to become one-toed
- astragalus (ankle bone) with a single "pulley"; developed plant-crushing molar teeth with a
loop-like enamel pattern
Major Perissodactyl Groups include the:
e1. Tapirs and Rhinoceroses
- include the largest land mammals known (Inthricotherines were rhinos up to 5.4 meters at the
shoulder)
e2. Chalicotheres
- Eocene-Pleistocene of North America, Eurasia and Africa
- Moropus (Miocene, North America) was a horse-sized clawed bipedal browser
e3. Horses
- Eocene to Recent
- evolutionary trends include increase in size and height, increased complexity of enamel pattern
on cheek teeth, elongation of legs, reduction of toes to one
e4. Brontotheres
- titanotheres (brontotheres) were medium- to very large-sized herbivores of the early Tertiary of
North America and eastern Asia
f. Artiodactyls
- "even toed" ungulates; includes pigs, camels, giraffes, deer, antelope, goats, sheep, cattle and
other extinct and modern groups; derived from the condylarths
- foot axis between the third and fourth digits; astragalus (ankle bone) forms a double-pulley
structure
- primitive stocks (Ex.= pigs) with complete dentition and often with enlarged canine tusks; later
stocks with upper incisors reduced or lost, with a diastema (an anterior gap in the toothrow),
HISTORICAL GEOLOGY LECTURE, PAGE 72
premolars become molar-like and the molar tooth cusps are crescent- or half-moon shaped
- with origin in the Paleocene; first radiation in early Eocene gave rise to many pig-like stocks
(forest and woodland rooters and browsers); second radiation in late Eocene and early Oligocene
gave rise to early ruminants (large herbivores); in Miocene ruminants diversified to exploit the
savannahs and grasslands and they remain the dominant herbivores there today [including
camels, giraffes, deer, cattle, antelopes, sheep, goats and extinct groups such as the oreodonts (a
very successful sheep-like artiodactyl group) and the protoceratids (a deer-like group with some
members having weird "nose horns")]
XVIII. Human Origins
A. Primates (Order Primates)
- it is possible that primates and rodents share a common ancestor in the late Cretaceous
- usually scansorial ("scurrying"), small- to medium-sized forest-dwelling herbivores or
omnivores
1. General Characteristics
- Skeleton - retain a primitive, generalized skeleton, with five fingers and toes on the hands and
feet; trend toward increasing the mobility of the thumb and big toe; orthograde (upright) posture;
typically cling or sit vertically when resting; locomotion generally quadrupedal
- Skull - facial part of skull is reduced in more advanced primates; nasal apparatus generally
reduced; eyes face forward on skull; brain relatively large; molars often form a "square" cusp
pattern
B. Primitive Primates and Primate-Like Groups
- there are a number of primitive groups of primates and primate-like mammals, often
differentiated on the basis of skull shape, tooth and ear morphology
1. Plesiadapiforms
- Late Cretaceous-Eocene; previously placed within the Primates (and still considered to
represent a sister group to them); Plesiadapids had a rodent-like dentition with a long diastema
("gap") between the procumbent incisors and grinding molar teeth (probably herbivorous diet)
2. Lemurs
- Lemurs are found in the Old World tropics; they are typically small, arboreal, nocturnal, furry,
with a fox-like face
C. Anthropoid Primates
- monkeys, apes and man (late Eocene - Recent)
- with derived features of the skull; molar cusps usually form a "square" pattern; braincase
expanded with the skull opening for the attachment of the vertebral column placed under the
skull (therefore the face is turned forward almost at a right angle to the backbone)
- substantial changes in global climates during the Miocene were due to the northward movement
of the African plate (created the Antarctic Circumpolar Current , and semi-arid savannah
HISTORICAL GEOLOGY LECTURE, PAGE 73
environments became dominant); the Old World "catarrhine" monkeys did well in this climate,
other primates didn't
1. Origin of the Hominoids
- based primarily on DNA evidence, it has been theorized that at approximately 5-6 Ma gorillas,
chimps and hominids (man's family) diverged when climate became cooler, drier and more
seasonal (termed the Messinian Climate Crisis)
a. Australopithecines
- the first "humans"
- Ardipithecus species were the earliest known australopithecines, including Ardipithecus
kadabba (ca. 5.7 Ma?) and Ardipithecus ramidus (ca. 4.5-4.3 Ma) from Ethiopia, Africa; consist
of gracile (lightly-built) australopithecines with chimp-sized brains that inhabited woodlands
- Ardipithecus was bipedal (as indicated by the pelvis and leg structure) but the “big toe” on the
foot was divergent (the foot could be used for “grasping”), suggesting Ardipithecus may have
nested and fed in trees
- Australopithecus species (ca. 4-2 Ma) were gracile (lightly-built) hominids; fully bipedal
(determined by hips, thigh bones and fossil footprints at Laetoli); very apelike in most of skeleton
with long arms and fingers; the brain is chimp-size (400-500 milliliters); moderate to marked
sexual dimorphism (males larger than females); height from 1.0 to 1.5 meters (3' 3" to 4' 11") and
weight from 30 to 70 kilograms (66 to 154 pounds); a "gracile" australopithecine probably lead to
Homo
- Paranthropus species (2.6-1.2 Ma) were robust (heavily-built) australopithecines; relatively
long arms; height 1.1 to 1.4 meters (3' 7" to 4' 7") and weight 40 to 80 kilograms (88 to 176
pounds); marked sexual dimorphism; prominent crests on top and back of skull; very long, broad,
flattish face; strong facial buttressing; very thick jaws; small incisors and canines; large, molarlike premolars; very large molars; brain size 410 to 530 milliliters
b. Homo
- the genus containing modern man
b1. Early Homo Species
- Homo rudolfensis (ca. 2.5 - 1.9 Ma) and Homo habilis (ca. 2.1 - 1.5 Ma) were similar to
Australopithecus but brain size increased to about 650-750 ml
The Oldowan Culture
- first tool culture; although the Oldowan Culture has considered to be a "pebble tool" culture,
their primary use appears to have been as choppers, scrapers and pounders; the Oldowan Culture
was probably due to Australopithecus gahri, Homo rudolfensis, H.habilis and early H. ergaster
- dates at 2.5 - 1.5 Ma; early humans used these tools for "expanding their niche" - cutting,
crushing, digging, projectiles and carrying; it appears that the hominids had no preconceived
shape of the tool during manufacture (i.e., no "mental template")
HISTORICAL GEOLOGY LECTURE, PAGE 74
- early Homo species may have lived in multi-male and multi-female groups; males competed for
access to females
- no evidence of intentional burials, grave goods, art, etc.; no clear evidence of architectural
features
b2. Homo ergaster
- approximately 1.9 to 1.5 Ma in eastern Africa
- may be ancestral to all subsequent Homo species
- the slender-bodied, long-legged "Turkana Boy" skeleton is essentially modern and with a highly
efficient striding structure; adults probably 1.8 meters tall (6') or more; brain size 800- 1050 ml
- oldest H. ergaster made Oldowan tools; at approximately 1.65 Ma developed Acheulian
industry (with large hand-held stone axes); may have been first to use fire at 1.7 Ma (fire
provides warmth, used in hunting, protection against predators, remove toxins from food)
b3. Homo erectus
- Asiatic form [ca. 1.5 Ma to 225 Ka] with a relatively large brain (850 -1150 ml), flat skull, large
brow ridges, sloped forehead, nuchal crest on back of skull, almost no chin; probably did not give
rise to later Homo species
b4. Origin of Homo sapiens
- probably evolved from H. ergaster-like species
- by 500 - 200 Ka with forms intermediate between H. ergaster/"erectus" and H. sapiens
Origin Theories for Homo sapiens include:
- Multi-Regional Hypothesis - evolution from several "stocks" of migrated Homo ergaster /
"erectus" (especially Africa and eastern Asia)
- Out-of-Africa Hypothesis - evolution from a single stock of H. ergaster / "erectus" that later
migrated (most popular theory) and replaced older groups
- Homo floresiensis, a tiny (adults 42 inches high!) island species from Indonesia, is similar to
Homo ergaster ; it may have lived as late as 18,000 years ago (if true, this greatly changes our
ideas of the diversity and distribution of ancient hominids)
b5. Homo neanderthalensis
- “early pre-Neandertals” at 400 Ka; Homo neanderthalensis at 150 Ka to 27 Ka; mostly lived in
Europe and western Asia
- often massive brow ridges; large cheek bones; protruding face; no chin; "bun"-shaped skull;
large cranial capacity (often greater than modern man); short (1.5 meters; 5 ft.) but very powerful
- probably not ancestral to Homo sapiens (with distinct DNA)
- hand axes decline, flake tradition becomes dominant
Mousterian Tradition
- usually attributed to Homo neanderthalensis
- strike flake from underside of a prepared "tortoise-shell" core to create many tool types; many
HISTORICAL GEOLOGY LECTURE, PAGE 75
of these were Composite Tools (artifacts made from more than one component)
b8. Homo sapiens sapiens
- Homo sapiens sapiens evolved from archaic H. sapiens in Africa and then replaced
neanderthals in Eurasia?
- there may have been an early dispersal of anatomically modern-looking Homo sapiens from
Africa at about 100 Ka; there may have been a substantial “bottleneck” of population after that,
with numbers dropping to as low as 10,000 individuals
- Homo sapiens sapiens developed the Upper Paleolithic tool technology (35 to 9 Ka); often
typified by "punch-struck" blade industries (a blade is a long flake); these were "specialized"
hunter-gatherers (concentrate on a few resources) that often hunted herd animals
Religion - Burials with ceremonial burials and grave goods
Upper Paleolithic Art - first widespread production of true art was by modern Homo sapiens (Ex.
= cave paintings), probably with a religious significance