Download GE 121 Physical and Historical Geology I Earth’s Dynamic Systems 10

GE 121 Physical and Historical Geology I
GE 122 Physical and Historical Geology II
Expanded course objectives
Earth’s Dynamic Systems 10th Edition
Hamblin, W.K. and Christiansen, E.H.
Planet Earth
Major Concepts
1. A comparison of Earth with other inner planets provides insight into the distinguishing
characteristics of our planet and what makes it unique.
2. Earth's atmosphere is a thin shell of gas surrounding the planet. It is a fluid, in constant
motion. Other planets have atmospheres, but Earth's is unique because it is 78%
nitrogen and 21% oxygen.
3. The hydrosphere is another feature that makes Earth unique. Water moves in a great,
endless cycle from the ocean to the atmosphere, over the land surface, and back to the
sea again.
4. The biosphere exists because of water. Although it is small compared to other layers of
Earth, it is a major geologic force operating at the surface.
5. Continents and ocean basins are the largest-scale surface features of Earth.
6. The continents consist of three major components: (a) ancient shields, (b) stable
platforms, and (c) belts of folded mountains. Each reveals the mobility of Earth's crust.
7. The ocean floor contains several major structural and topographic divisions: (a) the
oceanic ridge, (b) the vast abyssal floor, (c) trenches, (d) seamounts, and (e) continental
margins.
8. Earth is a differentiated planet, with its materials segregated into layers according to
density. The internal layers based on composition are (a) crust, (b) mantle, and (c) core.
The major internal layers based on physical properties are (a) lithosphere, (b)
asthenosphere, (c) mesosphere, (d) outer core, and (e) inner core. Material within each
of these units is in motion, making Earth a changing, dynamic planet.
Geologic Systems
Major Concepts
1. A natural system is a group of interdependent components that interact to form a unified
whole and are under the influence of related forces. The materials in a system change in
an effort to reach and maintain equilibrium.
2. Earth's system of moving water, the hydrologic system, involves the movement of
water—in rivers, as groundwater, in glaciers, in oceans, and as water vapor in the
atmosphere. As water moves, it erodes, transports, and deposits sediment, creating
distinctive landforms and rock bodies.
3. Radiation from the Sun is the source of energy for Earth's hydrologic system.
4. A system of moving lithospheric plates—the plate tectonic system—explains Earth's
major structural features. It operates from Earth's internal heat.
5. Where plates move apart, hot material from the mantle wells up to fill the void and
creates new lithosphere. The major features formed where plates spread apart are
continental rifts, oceanic ridges, and new ocean basins.
6. Where plates converge, one slides beneath the other and plunges down into the mantle.
The major features formed at convergent plate margins are folded mountain belts,
volcanic arcs, and deep-sea trenches.
7. Where plates slip horizontally past one another, transform plate boundaries develop on
long, straight faults. Shallow earthquakes are common.
8. Far from plate margins, plumes of less-dense mantle material rise to shallow levels,
feeding within-plate volcanoes and producing minor flexures of the lithosphere.
9. Earth's crust floats on the denser mantle beneath. The crust rises and sinks in attempts
to maintain isostatic equilibrium.
Minerals
Major Concepts
1. An atom is the smallest unit of an element that possesses the properties of the element.
It consists of a nucleus of protons and neutrons and a surrounding cloud of electrons.
2. An atom of a given element is distinguished by the number of protons in its nucleus.
Isotopes are varieties of an element, distinguished by the different numbers of neutrons
in their nuclei.
3. Ions are electrically charged atoms, produced by a gain or loss of electrons.
4. Matter exists in three states: (a) solid, (b) liquid, and (c) gas. The differences among the
three are related to the degree of ordering of the atoms.
5. A mineral is a natural solid possessing a specific internal atomic structure and a chemical
composition that varies only within certain limits. Each type of mineral is stable only under
specific conditions of temperature and pressure.
6. Minerals grow when atoms are added to the crystal structure as matter changes from the
gaseous or the liquid state to the solid state. Minerals dissolve or melt when atoms are
removed from the crystal structure.
7. All specimens of a mineral have well-defined physical and chemical properties (such as
crystal structure, cleavage or fracture, hardness, and density).
8. Silicate minerals are the most important minerals and form more than 95% of Earth's
crust. The most important silicates are feldspars, micas, olivines, pyroxenes, amphiboles,
quartz, and clay minerals. Important non-silicate minerals are calcite, dolomite, gypsum,
and halite.
9. Minerals grow and are broken down under specific conditions of temperature, pressure,
and chemical composition. Consequently, minerals are a record of the changes that have
occurred in Earth throughout its history.
Igneous Rocks
Major Concepts
1. Magma is molten rock that originates from the partial melting of the lower crust and the
upper mantle, usually at depths between 10 and 200 km below the surface.
2. The texture of a rock provides important insight into the cooling history of the magma.
The major textures of igneous rocks are (a) glassy, (b) aphanitic, (c) phaneritic, (d)
porphyritic, and (e) pyroclastic.
3. Most magmas are part of a continuum that ranges from mafic magma to silicic magma.
4. Silicic magmas produce rocks of the granite-rhyolite family, which are composed of
quartz, K-feldspar, Na-plagioclase, and minor amounts of biotite or amphibole.
5. Basaltic magmas produce rocks of the gabbro-basalt family, which are composed of Caplagioclase and pyroxene with lesser amounts of olivine and little or no quartz.
6. Magmas with composition intermediate between mafic and silicic compositions produce
rocks of the diorite-andesite family.
7. Basalt, the most abundant type of extrusive rock, typically erupts from fissures to produce
relatively thin lava flows that cover broad areas or from central vents to produce shield
volcanoes and cinder cones. Volcanic features developed by intermediate to silicic
magmas include viscous lava flows, ash-flow tuff, composite volcanoes, and collapse
calderas. The abundance of water in silicic magma is critical to its development and
eruption.
8. Masses of igneous rock formed by the cooling of magma beneath the surface are called
intrusions or plutons. The most important types of intrusions are batholiths, stocks, dikes,
sills, and laccoliths.
9. The wide variety of magma compositions is caused by variations in: (1) the composition
of the source rocks, (2) partial melting, (3) fractional crystallization, (4) mixing, and (5)
assimilation of solid rock into the molten magma.
10. Most basaltic magma is generated by partial melting of the mantle at divergent plate
boundaries and in rising mantle plumes. Most intermediate to silicic magma is produced
at convergent plate boundaries. Partial melting of continental crust at rifts and above
plumes can also produce silicic magma.
Sedimentary Rocks
Major Concepts
1. Sedimentary rocks are formed at Earth's surface by the hydrologic system. Their origin
involves the weathering of preexisting rock, transportation of the material away from the
original site, deposition of the eroded material in the sea or in some other sedimentary
environment, followed by compaction and cementation.
2. Two main types of sedimentary rocks are recognized: (a) clastic rocks and (b) chemically
precipitated rocks and organic rocks.
3. Stratification is the most significant sedimentary structure. Other important structures
include cross-bedding, graded bedding, ripple marks, and mud cracks.
4. The major sedimentary systems are (a) fluvial, (b) alluvial-fan, (c) eolian, (d) glacial, (e)
delta, (f) shoreline, (g) organic-reef, (h) shallow-marine,(i) submarine fan, and (j) deepmarine systems.
5. Sedimentary rock layers can be grouped into formations and formations can be grouped
into sequences that are bound by erosion surfaces. These formations and sequences
form an important interpretive element in the rock record.
6. Plate tectonics has had a profound effect on the genesis of sedimentary rocks by
controlling the geologic setting in which various types of sediment sequences are formed
and the climate zones into which continents drift.
Metamorphic Rocks
Major Concepts
1. Metamorphic rocks can be formed from igneous, sedimentary, or previously
metamorphosed rocks by recrystallization in the solid state. The driving forces for
metamorphism are changes in temperature, pressure, and composition of their pore
fluids.
2. These changes produce new minerals, new textures, and new structures within the rock
body. Careful study of metamorphic rocks reveals the thermal and deformation history of
Earth's crust.
3. The textures of metamorphic rocks are unique and tell their stories of solid-state
recrystallization and deformation. During metamorphism, new platy mineral grains grow
in the direction of least stress, producing a planar rock structure called foliation. Rocks
with only one mineral (such as limestone) or those that recrystallize in the absence of
deforming stresses do not develop strong foliation but instead develop a granular texture.
Mylonitic rocks develop where shearing along a fracture forms small grains by ductile
destruction of larger grains.
4. The major types of foliated metamorphic rocks include slate, schist, gneiss, and mylonite;
important nonfoliated rocks include quartzite, marble, hornfels, greenstone, and granulite.
They are distinguished by their textures and secondarily by their compositions.
5. Contact metamorphism is a local phenomenon associated with thermal and chemical
changes near the contacts of igneous intrusions. Regional metamorphism is best
developed in the roots of mountain belts along convergent plate boundaries.
6. Mineral zones are produced where temperature, pressure, or fluid compositions varied
systematically across metamorphic belts or around igneous intrusions.
7. Distinctive sequences of metamorphic rocks are produced in each of the major plate
tectonic settings.
Structure of Rock Bodies
Major Concepts
1. Deformation of Earth's crust is well documented by historical movement along faults, by
raised beach terraces, and by deformed rock bodies.
2. Folds in rock strata range in size from microscopic wrinkles to large structures hundreds
of kilometers long. The major types of folds are (a) domes and basins, (b) plunging
anticlines and synclines, and (c) complex folds.
3. Faults are fractures, along which slippage or displacement has occurred. The three basic
types are (a) normal faults, (b) thrust faults, and (c) strike-slip faults.
4. Joints are fractures in rocks along which there is no horizontal or vertical displacement.
5. Rocks deform when applied stress exceeds their strength. They may deform by ductile
flow or brittle fracture.
Geologic Time
Major Concepts
1. The interpretation of past events in Earth's history is based on the principle that the laws
of nature do not change with time.
2. Relative dating (determining the chronological order of a sequence of events) is achieved
by applying the principles of (a) superposition, (b) faunal succession, (c) crosscutting
relations, (d) inclusions, and (e) succession in landscape development.
3. The standard geologic column was established from studies of rock sequences in
Europe. It is now used worldwide. Rocks were originally correlated from different parts of
the world largely based on the fossils they contain. Today, radiometric dating can be
used to correlate major rock sequences.
4. Numerical time designates a specific duration of time in units of hours, days, or years. In
geology, long periods of absolute time can be measured by radiometric dating.
Weathering
Major Concepts
1. Weathering is the breakdown and alteration of rocks at Earth's surface through physical
and chemical reactions with the atmosphere and the hydrosphere.
2. Physical weathering is the mechanical fragmentation of rocks from stress acting on them.
Ice wedging may be the most important type.
3. Chemical weathering involves chemical reactions with minerals that progressively
decompose the solid rock. The major types of chemical weathering are dissolution, acid
hyrdolysis, and oxidation.
4. Joints and fractures facilitate weathering because they permit water and gases in the
atmosphere to attack a rock body at considerable depth. They also greatly increase the
surface area on which chemical reactions can occur.
5. The major products of weathering are spheroidal rock forms, a blanket of regolith, and
dissolved ions. Soil is the upper part of the regolith—a mixture of clay minerals,
weathered rock particles, and organic matter.
6. Climate greatly influences the type and rate of weathering.
Slope Systems
Major Concepts
1. Mass movement is the downslope transfer of material through the direct action of gravity.
It is a major geologic process operating on all slopes.
2. The most important factors influencing slope failures are saturation of slope material with
water, earthquakes, over steepening of slopes, and freezing and thawing.
3. The major types of mass movement are creep, debris flows, landslides, and subsidence.
4. Creep is the very slow downslope movement of soil and rock, produced primarily by the
expansion and contraction of the surface materials.
5. Debris flows are mixtures of rock fragments and water that flow downslope as a viscous
fluid. A lahar is a special type of debris flow composed of volcanic materials.
6. Landslides are a type of mass movement in which the material moves as a unit or block
along definite slippage planes.
7. Subsidence differs from other types of mass movement in that it has essentially vertical
motion caused by collapse into voids or as a result of compaction of loose materials.
8. Slopes are open dynamic systems in which regolith and near-surface bedrock move
downslope toward the main stream, where they are removed through the drainage
system.
River Systems
Major Concepts
1. Running water is part of Earth's hydrologic system and is the most important agent of
erosion. Stream valleys are the most abundant and widespread landforms on the
continents.
2. A river system consists of a main channel and all of the tributaries that flow into it. It can
be divided into three subsystems: (1) a collecting system, (2) a transporting system, and
(3) a dispersing system.
3. The most important variables in stream flow are (1) discharge, (2) velocity, (3) gradient,
(4) sediment load, and (5) base level.
4. The variables in a stream constantly adjust toward a state of equilibrium.
5. Rivers erode by (1) removing regolith, (2) downcutting, and (3) headward erosion.
6. As a river develops a low gradient, it deposits part of its load on point bars, on natural
levees, and across the surface of its floodplain.
7. Most of a river's sediment is deposited where the river empties into a lake or ocean. This
deposition commonly builds a delta at the river's mouth. In arid regions, many streams
deposit their loads as alluvial fans at the base of steep slopes.
8. The origin and evolution of the world's major rivers are controlled by the tectonic and
hydrologic systems.
Groundwater Systems
Major Concepts
1. Groundwater is an integral part of the hydrologic system, and it is intimately related to
surface water drainage.
2. The movement of groundwater is controlled largely by the porosity and permeability of
the rocks through which it flows.
3. The water table is the upper surface of the zone of saturation.
4. Groundwater moves slowly through the pore spaces in rocks by the pull of gravity.
5. The natural discharge of groundwater is generally into springs, streams, marshes, and
lakes.
6. Artesian water is confined under pressure, like water in a pipe. It occurs in permeable
beds bounded by impermeable formations.
7. Erosion by groundwater produces karst topography, which is characterized by caves,
sinkholes, solution valleys, and disappearing streams. Precipitation of minerals from
groundwater creates deposits in caves and along fractures and cements many kinds of
clastic sedimentary rocks.
8. Alteration of the groundwater system can produce many unforeseen problems, such as
pollution, subsidence, sinkhole collapse, and disruption of ecosystems.
Glacial Systems
Major Concepts
1. Glaciers are systems of flowing ice that form where more snow accumulates each year
than melts.
2. As ice flows, it erodes the surface of the land by abrasion and plucking. Sediment is
transported by the glacier and deposited where the ice melts. In the process, the
landscape is greatly modified.
3. The two major types of glaciers—continental and valley glaciers—produce distinctive
erosional and depositional landforms.
4. The Pleistocene ice age began 2 to 3 million years ago and terminated, in most areas,
about 5,000 years ago. During the ice age, there were a number of glacial and
interglacial epochs.
5. The major effects of an ice age include glacial erosion and deposition, modification of
drainage systems, creation of numerous lakes, the fall of sea level, isostatic adjustments
of the lithosphere, and migration and selective extinction of plant and animal species.
6. Periods of glaciation have been rare events in Earth's history. The causes of glacial
episodes are not completely understood, but they may be related to several
simultaneously occurring factors, such as astronomical cycles, plate tectonics, and ocean
currents.
Shoreline Systems
Major Concepts
1. Wind-generated waves provide most of the energy for shoreline processes.
2. Wave refraction concentrates energy on headlands and disperses it in bays.
3. Longshore drift, generated by waves advancing obliquely toward the shore, transports
sediment parallel to the coast. It is one of the most important shoreline processes.
4. Erosion along a coast tends to develop sea cliffs by the undercutting action of waves and
longshore currents. As a cliff recedes, a wave-cut platform develops, until equilibrium is
established between wave energy and the shape of the coast.
5. Sediment transported by waves and longshore current is deposited in areas of low
energy to form beaches, spits, and barrier islands.
6. Erosion and deposition along a coast tend to develop a straight or gently curving
shoreline that is in equilibrium with the energy expended upon it.
7. Reefs grow in tropical climates and thrive only in shallow, clear marine waters. Fringing
reefs around volcanic islands can evolve into atolls.
8. The worldwide rise in sea level, associated with the melting of the Pleistocene glaciers,
drowned many coasts between 15,000 and 20,000 years ago. Coasts are classified
based on the process—subaerial or marine—that has been most significant in developing
their configurations or upon their tectonic setting.
9. Tides are produced by the gravitational attraction of the Moon and locally exert a major
influence on shorelines.
10. Tsunamis are waves generated by earthquakes, volcanic eruptions, and submarine
landslides that disturb the sea floor.
Eolian Systems
Major Concepts
1. Wind is not an effective agent in eroding the landscape, but it can produce deflation
basins and yardangs as well as small pits and grooves on rocks.
2. The major result of wind activity is the transportation of loose, unconsolidated fragments
of sand and dust. Wind transports sand by saltation and surface creep. Dust is
transported in suspension, and it can remain high in the atmosphere for long periods.
3. Sand dunes migrate as sand grains are blown up and over the windward side of the dune
and accumulate on the lee slope. The internal structure of a dune consists of strata
inclined in a downwind direction.
4. Various types of dunes form, depending on wind velocity, sand supply, constancy of wind
direction, and characteristics of the surface over which the sand migrates.
5. Windblown dust (loess) forms blanket deposits, which can mask the older landscape
beneath them. The source of loess is desert dust or the fine rock debris deposited by
glaciers.
6. Desertification, the loss of farmable land on the margins of deserts, can be caused by
human activity or by slight climatic fluctuations
Plate Tectonics
Major Concepts
1. The theory of continental drift was proposed in the early 1900s and was supported by a
variety of geologic evidence. Without knowledge of the nature of the oceanic crust,
however, a complete theory of Earth's dynamics could not have been developed.
2. A major breakthrough in the development of the plate tectonics theory occurred in the
early 1960s when the topography of the ocean floors was mapped and magnetic and
seismic characteristics of the oceanic crust were determined.
3. Most tectonic activity occurs along plate boundaries. Divergent plate boundaries are
zones where the plates split and spread apart. Convergent plate boundaries are zones
where plates collide. Transform fault boundaries are zones where plates slide horizontally
past each other.
4. The direction of the relative motion of plates is indicated by (a) the trend of the oceanic
ridge and associated transform faults, (b) seismic data, (c) magnetic stripes on the
seafloor, and (d) the ages of chains of volcanic islands and seamounts. The motion of a
plate can be described in terms of rotation around a pole.
5. Heat flow from the core and the mantle (generated by radioactivity) is probably the
fundamental cause of Earth's internal convection.
6. The major forces acting on plates are (a) slab-pull, (b) ridge-push, (c) basal drag, and (d)
friction along transform faults and in subduction zones. The most important forces that
make the plates move are probably slab-pull and ridge push.
Seismicity and Earth's Interior
Major Concepts
1. Seismic waves are vibrations in Earth caused by the rupture and sudden movement of
rock.
2. Three types of seismic waves are produced by an earthquake shock: (a) P waves, (b) S
waves, and (c) surface waves.
3. The primary effect of an earthquake is ground motion. Secondary effects include (a)
landslides, (b) tsunamis, and (c) regional or local uplift or subsidence.
4. The exact location and timing of an earthquake cannot be predicted. However, seismic
risk can be evaluated and, in areas with high risk, preparations for future earthquakes
can be made.
5. Most earthquakes occur along plate boundaries. Divergent plate boundaries and
transform fault boundaries produce shallow-focus earthquakes. Convergent plate
boundaries produce an inclined zone of shallow-focus, intermediate-focus, and deepfocus earthquakes.
6. The velocities at which P waves and S waves travel through Earth indicate that Earth has
a layered internal structure based on composition—crust, mantle, and core. It also has a
solid inner core, a liquid outer core, a weak asthenosphere, and a rigid lithosphere.
7. Plate tectonics and upwelling and downwelling plumes are the most important
manifestations of Earth's internal convection. The magnetic field is probably caused by
convection of the molten iron core.
Divergent Plate Boundaries
Major Concepts
1. Divergent plate boundaries are zones where lithospheric plates move apart from one
another. They are characterized by tensional stresses that typically produce long rift
zones, normal faults, and basaltic volcanism.
2. An oceanic ridge marks divergent plate boundaries in the ocean basins. It is a broad
fractured swell with a total length of about 70,000 km. Basaltic volcanism and
earthquakes are concentrated along the rift zone at the ridge crest.
3. The ridge is broken into segments and its characteristics depend upon the rate of
spreading.
4. Oceanic crust is generated at divergent plate boundaries and is composed of four major
layers: (a) deep marine sediment, (b) pillow basalts, (c) sheeted dikes, and (d) gabbro.
Below the crust lies a zone of sheared peridotite in the upper mantle.
5. At divergent plate boundaries, basaltic magmatism results from decompression melting of
the mantle. The magma then collects into elongate chambers beneath the ridge and
some is intruded as dikes or extruded along the rift zone.
6. As the oceanic lithosphere moves away from the ridge it cools, becomes thicker and
more dense, and subsides.
7. Seawater is heated as it circulates through the hot crust and causes extensive
hydrothermal alteration and large volumes of metamorphosed basalt. Locally, the
hydrothermal fluid vents to produce hot springs on the seafloor.
8. Continental rifting occurs where divergent plate margins develop in continents. The East
African rift, the Red Sea, and the Atlantic Ocean show various steps in a progression
from continental rifting to seafloor formation.
9. Continental rifting creates new continental margins marked by normal faults and volcanic
rocks interlayered with thick sequences of continental sedimentary rocks. As the
continental margin subsides, it is gradually buried by a thick layer of shallow marine
sediments.
Transform Plate Boundaries
Major Concepts
1. Transform plate boundaries are unique, in that the plates move horizontally past each
other on strike-slip faults. Lithosphere is neither created nor destroyed.
2. The three major types of transform boundaries are: (1) a ridge-ridge transform, which
connects two segments of a divergent plate boundary; (2) a ridge-trench transform, which
connects a ridge and a trench; and (3) a trench-trench transform, which connects two
convergent plate boundaries.
3. Transform plate boundaries are shearing zones where plates move past each other
without diverging or converging. In the shearing process, secondary features are created,
including parallel ridges and valleys, pull-apart basins, and belts of folds. Compression
and extension develop only in small areas.
4. Oceanic fracture zones are prominent linear features that trend perpendicular to the
oceanic ridge. They may be several kilometers wide and thousands of kilometers long.
The structure and topography of oceanic fracture zones depend largely on two things: the
temperature (or age) difference across the fracture, and the spreading rate of the oceanic
ridge.
5. Continental transform fault zones are similar to oceanic transforms, but they lack fracture
zone extensions.
6. Shallow earthquakes are common along transform plate boundaries; they are especially
destructive on the continents.
7. Volcanism is rare along transform plate boundaries, but small amounts of basalt erupt
locally from leaky transform faults.
8. Metamorphism in transform fault zones creates rocks with strongly sheared fabrics, as
well as hydrated crustal and even mantle rocks.
Convergent Plate Boundaries
Major Concepts
1. Convergent plate boundaries are zones where lithospheric plates collide. The three major
types of convergent plate interactions are (a) convergence of two oceanic plates, (b)
convergence of an oceanic and a continental plate, and (c) collision of two continental
plates. The first two involve subduction of oceanic lithosphere into the mantle.
2. Plate temperatures, convergence rates, and convergence directions play important roles
in determining the final character of a convergent plate boundary.
3. Most subduction zones are marked by an outer swell, a trench and forearc, a magmatic
arc, and a backarc basin. In contrast, continental collision produces a wide belt of folded
and faulted mountains in the middle of a new continent.
4. Subduction of oceanic lithosphere produces a narrow, inclined zone of earthquakes that
extends to more than 600 km depth, but broad belts of shallow earthquakes form where
two continents collide.
5. Crustal deformation at subduction zones produces melange in the forearc, and extension
or compression in the volcanic arc and backarc areas. Continental collision is always
marked by strong horizontal compression that causes folding and thrust-faulting.
6. Magma is generated at subduction zones because dehydration of oceanic crust causes
partial melting of the overlying mantle. Andesite, and other silicic magmas that commonly
erupt explosively, are distinctive products of convergent plate boundaries. At depth,
plutons form, composed of rock ranging from diorite to granite. In continental collision
zones, magma is less voluminous, dominantly granitic, and probably derived by melting
of preexisting continental crust.
7. Metamorphism at subduction zones produces low-temperature/high-pressure facies near
the trench and higher-temperature facies near the magmatic arc. Broad belts of highly
deformed regional metamorphic rocks mark the sites of past continental collision.
8. Continents grow larger as low-density silica-rich rock is added to the crust at convergent
plate boundaries.
Hotspots and Mantle Plumes
Major Concepts
1. Mantle plumes appear to be long, nearly vertical columns of hot, upwelling solids that
ascend from the core-mantle boundary. They rise upward because they are lower in
density and therefore buoyant. At the surface, they create hotspots with high heat flow,
volcanic activity, and broad crustal swells.
2. A plume evolves in two stages. When a plume starts, it develops a large, bulbous head
that rises through the mantle. As the head deforms against the strong lithosphere, crustal
uplift and voluminous volcanism occur. The second stage is marked by the effects of a
still rising but narrow tail.
3. Basaltic magma is created because of decompression of the rising hot plume. Magmas
formed in mantle plumes are distinctive and show hints of being partially derived from
ancient subducted slabs that descended deep into the mantle.
4. A starting plume that rises beneath the ocean floor produces a large plateau of flood
basalt on the seafloor. Subsequently, a narrow chain of volcanic islands forms above the
tail of the plume, revealing the direction of plate motion.
5. If a plume develops beneath a continent, it may cause regional uplift and eruption of
continental flood basalts. Rhyolitic caldera systems develop when continental crust is
partially melted by hot basaltic magma from the plume. Continental rifting and the
development of an ocean basin may follow.
6. Plumes may affect the climate system and Earth's magnetic field.
Other Planets
Major Concepts
1. Impact cratering was the dominant geologic process in the early history of all planetary
bodies in the solar system.
2. Earth, the Moon, Mercury, Venus, and Mars form a family of related planets, known as
the inner planets, that probably experienced similar sequences of events in their early
histories.
3. Both the Moon and Mercury are primitive bodies, and their surfaces have not been
modified by hydrologic and tectonic systems. Much of their surfaces are ancient and
heavily cratered.
4. Mars has had an eventful geologic history involving crustal uplift, volcanism, stream
erosion, and eolian activity. Huge tracts of cratered terrain remain but are intensely
eroded. Liquid water may have existed on its surface, and there is controversial new
evidence that life may have evolved there.
5. The surface of Venus is dominated by relatively young volcanic landscapes and such
tectonic features as faults and folded mountain belts. The crust of Venus does not appear
to be broken into tectonic plates, however, and much of its evolution is related to the
development of mantle plumes.
6. Cratering on the icy moons of Jupiter, Saturn, Uranus, and Neptune suggests that a
period of intense bombardment affected the entire solar system more than 4 billion years
ago.
7. Most of the icy moons of Uranus and Neptune show evidence of geologic activities such
as volcanic extrusions of slushy ice and rifting.
8. Asteroids and comets are the smallest members of the solar system. They appear to be
remnants of the bodies that accreted to form the larger planets.
9. The planets formed in a thermal gradient around the Sun. The inner planets are thus rich
in silicates and iron, which are stable at high temperature, and the outer planetary bodies
have large amounts of ice, which is stable at low temperature.
10. The geologic evolution of a planet depends on its source of heat energy, its size, and its
composition.
Evolution of the Earth
Donald R. Prothero / Robert H. Dott, Jr.
Tabel Of Contents
Chapter 1
Time and Terrestrial Change 3
Dramatic Geologic Events in Human History 4
Subtle Geologic Events in Human History 6
Climate 6
Glaciers and Sea Level 7
Crustal Changes 8
Box 1.1 Human Beings as Geologic Agents 9
How Fast Is Fast? Time and Rates of Geologic Processes 9
Examples of Rates 10
Different Ways of Growing and Changing 11
Catastrophic Versus Uniform Views of Change and the Age of the Earth 12
Summary 13
Readings 13
Chapter 2
Floods, Fossils, and Heresies 15
What Is a Fossil? 16
Early Questions 16
Da Vinci’s Insight 17
Steno’s Principles 17
Utility of Fossils 18
Fossils and Geologic Mapping 18
Box 2.1 Robert Hooke and the Meaning of Fossils 18
Principle of Fossil Correlation and Index Fossils 22
Explanations of Change Among Fossils 22
Catastrophism 22
Descent by Evolution 23
Box 2.2 Mark Twain Winks at Paleontology 24
First Unified Hypotheses of the Earth 24
The Cosmogonists 24
Buffon’s Break with Genesis 24
The First True Geologic Chronology 24
Neptunism 25
A. G. Werner 25
Heated Basalt Controversy 26
Plutonism—the Beginning of Modern Geology 26
James Hutton 26
An Old Dynamic Earth 26
“Nothing in the Strict Sense Primitive” 27
Basalt 27
Granite and Mineral Veins 27
Evidence of Upheaval of Mountains 27
Charles Lyell’s Uniformity of Nature 29
Evolution—Lyell’s Ultimate Challenge 30
Box 2.3 Uniformitarianism in the Public Eye 30
Equilibrium and Feedback 31
The Doctrine of Uniformity Today 31
Scientific Methodology of Geology 32
Historical Science 32
Geologic Reasoning 32
Box 2.4 Gradualism Meets the Scablands 33
Summary 35
Readings 36
Chapter 3
Evolution 39
The Evolution of Evolution 40
Buffon’s Evolution 40
Erasmus Darwin: Did He Begin It All? 41
Lamarckian Evolution 41
Inheritance of Acquired Characteristics 42
Charles Darwin and Natural Selection 43
Evidence of Evolution 45
Reality of Evolution 50
Genetics and the Evolutionary Synthesis 50
Box 3.1 Mendelian Genetics and Molecular Biology 51
The Origin of Species 53
The Fossil Record and Evolution 55
Challenges to the Neo-Darwinian Synthesis 58
Neutralism 58
Inheritance of Acquired Characteristics Revisited 59
Macroevolution 59
Evolution and Creationism 62
Summary 63
Readings 65
Chapter 4
The Relative Geologic Time Scale and Modern Concepts of Stratigraphy 67
Early Mapping and Correlation of Strata 68
Modern Relative Time Scale 69
Box 4.1 Nothing Quite Like a Good Fight . . . 71
Rocks Versus Time 71
Box 4.2 Corollaries to Superposition for Determining Relative Age 72
The Formation 73
Lateral Variations 73
Depositional Environments and Sedimentary Facies 74
Definition of Sedimentary Facies 74
Regional Analysis of Facies 75
Transgression and Regression by the Sea 75
Local Versus Worldwide Transgression and Regression 78
Biostratigraphic Concepts 78
Unconformities 80
Some Refinements 80
Unconformity-Bounded Sequences 81
Additional Relative Time Scales 81
A Sense of Time and Rates 83
Summary 83
Readings 84
Chapter 5
The Numerical Dating of the Earth 87
Early Attempts to Date the Earth 88
Kelvin’s Dating of the Earth 88
Box 5.1 Absolute Measures of Time 89
Radioactivity 90
First Dating of Minerals 91
Concept of Decay 91
Box 5.2 Mathematics of Radioactive Decay 92
Modern Isotopic Dating 92
Decay Series Used 92
Daughter Lead Ratios 93
Carbon 14—A Special Case 94
Fission-Track Dating 95
Discordant Dates from Resetting 95
Accuracy of Isotopic Dates 96
Isotopic Time Scale 96
Memorable Dates 97
An Assessment 98
Summary 98
Readings 99
Chapter 6
The Origin and Early Evolution of the Earth 101
Distribution of the Elements 102
Probable Origin of the Earth 102
Hot Origins 102
A Cold Beginning 103
Solar Nebula 103
Recent Modifications 104
Planetology of the Inner Solar System 106
Leftovers—Asteroids, Meteorites, and Comets 107
Nature of the Earth’s Interior 107
Early Speculations 107
Analogies from Meteorites 107
Seismological Evidence of Internal Structure 108
Further Evidence from the Magnetic Field 108
Chemical Composition of the Deep Interior 110
Box 6.1 Major Minerals and Rocks of the Earth’s Crust and Upper Mantle 111
Dawn of Earth History 111
Chemical and Thermal Evolution 111
Origin of the Crust 112
Origin and Evolution of the Atmosphere and Seawater 114
The Problem 114
Outgassing Hypothesis 114
Photochemical Dissociation Hypothesis 114
Oxygen from Photosynthesis 115
Origin of Seawater 116
Ocean-Atmosphere Regulatory Systems 116
Global Chemostat 116
Global Thermostat and Climate 117
Summary 118
Readings 119
Chapter 7
Mountain Building and Drifting Continents 121
Orogenic Belts and Mountain Building 122
The Geosynclinal Concept—Made in America 122
Vertical versus Horizontal Tectonics 124
A Cooling and Shrinking Earth 124
Continental Drift as a Cause of Mountain Building 125
Thermal Convection—Panacea for Mountain Building and Drift? 126
Drift in Eclipse 127
Paleomagnetism—Drift’s Renaissance 127
General Nature of the Sea Floor 130
Rates of Continental Erosion and Oceanic Sedimentation 130
Ocean Ridges 130
Sea-Floor Spreading—A Breakthrough 132
Rifts and Hot Mantle Plumes 132
Age Distribution of Oceanic Islands and Seamounts 133
Major Oceanic Escarpments and Transform Faults 134
Confirmation of Sea-Floor Spreading 135
Sea-Floor Magnetic Anomalies 135
Magnetic-Polarity-Reversal Time Scale 136
Spreading History 137
Plate Tectonics 138
What Drives Them? 140
Plate Collisions 140
Subsidence of Plates and the Accumulation of Sediments 142
Causes of Subsidence 143
Plate Tectonics and Sedimentary Basins 143
Summary 147
Readings 148
Chapter 8
Cryptozoic History: An Introduction to the Origin of Continental Crust 151
Box 8.1 How to Define the Base of the Phanerozoic? 152
Development of a Cryptozoic Chronology 153
Sedgwick in Wales 153
Canadian Shield 153
The Great Lakes Region 154
Great Lakes Correlations 157
Correlation Beyond the Great Lakes 157
Evidence of Crustal Development from Igneous and Metamorphic Rocks 159
Importance of Granite 159
Significance of Isotopic Date Patterns 160
Interpretation of Crustal Development from Sediments 162
Bias of the Record 162
Terrigenous Versus Nonterrigenous Sediments 162
Textural Maturity 162
Box 8.2 Geology’s First Important Instrument 163
Compositional Maturity 163
Stratification 163
The Cryptozoic Sedimentary and Volcanic Record 165
Ancient Archean Rocks 165
Early and Middle Proterozoic Sediments 167
Late Proterozoic Rocks 169
The Cryptozoic Ocean and Atmosphere 170
Orthodox View 170
An Alternative View 171
Box 8.3 Possible Highlights in the Chemical Evolution of the Cryptozoic AtmosphereOcean System 172
Cryptozoic Climate 174
Meager Evidence 174
Early Proterozoic Glaciation 174
Late Proterozoic Glaciation 174
Summary 177
Readings 178
Chapter 9
Early Life and Its Patterns 181
The Origin of Life 182
Early Concerns 182
“A Warm Little Pond?” 183
Chicken-or-Egg Problem: RNA or Proteins? 184
Box 9.1 Communities
Without Sunlight: Deep-Sea Hydrothermal Vent Faunas 185
Mud, Kitty Litter, and Fool’s Gold 186
The Record of Early Life Before the Paleozoic 187
Metazoans, Vendozoans, and the “Cambrian Explosion” 192
Darwin’s Dilemma 192
Cambrian Explosion of Shelly Invertebrates 193
When the Trilobites Roamed 197
Summary 204
Readings 204
Chapter 10
Earliest Paleozoic History: The Sauk Sequence—An Introduction to Cratons and Epeiric
Seas 207
Box 10.1 “SWEATing” It Out 208 Vendian History 209
The Cambrian Craton 210
Structural Modifications of Cratons 210
Development of Arches and Basins 212
Box 10.2 A Primer on Geologic Maps and Diagrams 215
The Sauk Transgression 219
General Setting 219
Mature Quartz Sandstones 220
Change to Carbonate Deposition 222
Importance of Oolite 223
Depth of the Sauk Sea 223
Modern Analogues for the Sauk Epeiric Sea 224
Importance of Episodic Events 226
Early Paleozoic Paleoclimate 227
Summary 228
Readings 229
Chapter 11
The Later Ordovician:
Further Studies of Plate Tectonics and the Paleogeography of Orogenic Belts 231
Ordovician Life 232
Explosive Radiation of the “Paleozoic Fauna” 232
Ordovician Extinctions 240
Ordovician History of the North American Craton 240
Mid-Ordovician Regression and the St. Peter Sandstone 240
Later Ordovician (Tippecanoe) Epeiric Sea 241
Shaly Deposits of Later Ordovician Time 241
Box 11.1 Unconformity-Bounded Sequences Revisited 242
Cratonic Basins and Arches 245
Ordovician Mountain Building in the Appalachian Orogenic Belt 245
Evidence of Increasing Structural Mobility 245
Box 11.2 Dividends from Volcanic Ash 246
Evidence for Dating the Mountain Building 246
Paleogeography and Sedimentation Within Orogenic Belts 247
Background 247
Early Ideas About Borderlands 247
Modern Concepts of Borderlands 248
A Modern Analogue 249
Controversy About Sea Level and Sedimentation 250
Plate-Tectonic Interpretation of Taconian Mountain Building 252
Early Paleozoic Passive-Margin Shelf 252
Thrust Loading of the Continental Margin by Collision 253
Relations Across the Atlantic 254
Summary 256
Readings 257
Chapter 12
The Middle Paleozoic: Time of Reefs, Salt, and Forests 259
Middle Paleozoic Life 260
Marine Communities 260
The Age of Fishes 262
Invasion of the Land 264
Late Devonian Mass Extinctions 268
Box 12.1 Fossils as Calendars 270
The Silurian and Early Devonian Continent 271
Aftermath of the Taconian Orogeny 271
A Carbonate-Rich Craton 272
Modern Versus Ancient Carbonate Sedimentation 274
Organic Reefs 275
General Characteristics 275
Silurian and Devonian Organic Reefs 277
Box 12.2 Origin of Dolomite Rocks 278
Marine Evaporite Deposits 279
Restricted-Basin Evaporites 279
Supratidal Sabkha Evaporites 282
Postdepositional Changes 283
The Michigan Basin 283
Paleoclimate and Paleogeography 283
Devonian Strata of the North American Craton 284
Regression and Transgression Again 284
Cratonic Basin Deposition 284
Cratonic Arches 288
The Acadian Orogeny in the Appalachian Belt 289
Evidence of Devonian Orogeny 289
Dating the Orogeny 290
The Catskill Clastic Wedge 291
The Chattanooga Black Shale Enigma 291
The Caledonian Orogenic Belt 291
Structural Symmetry 291
Box 12.3 Origin of Petroleum 292
Catskill-Old Red Sandstone Facies 293
Intracratonic Orogenic Belts 293
Mountain Building in the Arctic and Western Cordillera 294
Physical and Organic Evolution 295
Summary 296
Readings 297
Chapter 13
Late Paleozoic History: A Tectonic Climax and Retreat of the Sea 299
Mississippian Rocks 300
Last Widespread Carbonates 300
Sedimentary and Tectonic Changes 301
Late Paleozoic Repetitive Sedimentation 304
Sedimentary Cycles 304
Coal Swamps 308
Paleogeographic Reconstruction 309
Terminal Paleozoic Emergence of the Continent 310
Permo-Triassic Paleoclimate 310
Box 13.1 The Red Color Problem 313
Tectonics 315
Cratonic Disturbances 315
Appalachian Orogeny 315
Significance of Thrust Faulting 317
Late Paleozoic Mountain Building in Eurasia 320
Gondwanaland 321
The Gondwana Rocks 322
Box 13.2 Paleomagnetic Reconstruction for Drifting Continents 323
Glossopteris Flora 326
Animal Fossils 327
Antarctica—A Triumph of Prediction 327
Paleogeography and Paleoclimate of Pangea 328
Pangean Biogeography 330
Late Paleozoic Life 332
Marine Life 332
Pennsylvanian Coal Swamps and Permian Coniferous Forests 336
Box 13.3 The Advantages of Seeds 339
Swamp Dwellers and Synapsids 340
The Late Permian Catastrophe 344
Summary 347
Readings 348
Chapter 14
The Mesozoic Era: Age of Reptiles and Continental Breakup 351
Extensional Tectonics—Opening of the North Atlantic 352
The Newark Rifts 352
Ocean Basins and Aulacogens 353
The Breakup of Pangea 355
Triassic History of the Craton 355
Jurassic History of the Craton 359
Ancient Navajo Desert 359
Return of the Epeiric Sea 359
The Cordillera 361
Birth of a Mountain Belt 361
Suspect Terranes 363
Sonomia and the Sierran Arc 366
Granitic Rocks of the Sierran Arc 369
Foreland and Forearc Basins 369
The Sevier and Laramide Orogenies 371
Cretaceous Transgression and Sedimentation 376
Worldwide Effects 376
Effects on the Craton 376
Effects in Gulf and Atlantic Coastal Plains 378
Late Mesozoic Paleoclimatology 378
Paleontologic and Sedimentary Evidence 378
Oxygen-Isotope Paleothermometers 379
Cretaceous Climate 379
The Black Shale Problem 379
Life in the Mesozoic 382
The Mesozoic Marine Revolution 382
Marine Vertebrates 387
The Age of Dinosaurs 389
Saurischians and Birds 390
Box 14.1 A Tooth, A Rib, and Some Footprints 394
Box 14.2 Hot or Cold Running Dinosaurs? 398
Ornithischians 399
Flower Power 401
Early Mammals 403
Late Cretaceous Extinctions 404
Fossil Evidence 404
The Impact Hypothesis 406
The Volcanic Hypothesis 407
The Regression Hypothesis 407
An Assessment 408
Summary 410
Readings 411
Chapter 15
Cenozoic History: Threshold of the Present 413
Cenozoic Cordilleran History 414
Phase I: Laramide Orogeny
(Latest Cretaceous to Middle Eocene, 70 to 40 m.y. Ago) 414
Phase II: Resumption of Arc Volcanism (Late Eocene–Middle Miocene, 40 to 20 m.y.
Ago) 416
Phase III: Complex Teconism (Early Miocene–Present, 20 to 0 m.y. Ago) 422
Tectonic Hypothesis for the Evolution of the Cordillera 429
Pacific Tectonics 432
The Hawaiian Mantle Plume 432
Western and Southern Pacific Tectonics 433
Southeastern Pacific Tectonics 433
Cenozoic Tectonics of Eurasia 434
Early Cenozoic Events 434
The Alpine-Himalayan Belt of Eurasia 434
Effect of India’s Collision with Southeastern Asia 436
When the Tethys Dried Up 437
Cratonic Rifting and Mantle Plumes 437
Coastal Plains and Continental Shelves 440
Passive Successors of and Predecessors to Orogenic Belts 440
Gulf of Mexico Coastal Province 440
The Atlantic Coastal Province and Rejuvenation 441
Cenozoic Climate 443
Life in the Marine Realm 446
The Age of Mammals 449
The Early Cenozoic Adaptive Explosion 449
Paradise Lost 453
Family Trees 453
The Southern Continents 457
Summary 460
Readings 461
Chapter 16
Pleistocene Glaciation and the Advent of Humanity 465
What Is the Pleistocene? 466
Recognition of Continental-Scale Glaciation—A Triumph of Reasoning 466
Diverse Effects of Glaciation 468
General 468
Isostasy 468
Lakes 468
Wind Effects 469
Worldwide Changes in Sea Level 469
Pleistocene Chronology 469
What Caused Glaciations? 479
Climatologic Background 479
Late Cenozoic Climatic Deterioration 479
Types of Glacial Hypotheses 480
Astronomical, or Orbital, Hypotheses 481
Hypotheses of Changing Heat Budget 483
Hypotheses of Paleogeographic Causes 483
The Thermohaline Conveyor Belt and Dansgaard-Oeschger Cycles 484
Where Do We Stand? 485
Pleistocene Climatic Effects upon Life 485
Ranges of Organisms 485
Land Bridges 486
The End of an Era 486
The Evolution of Primates and Humans 489
The Early Hominid Record 492
The Genus Homo 494
Human Entry into America 496
Climate in Human History 496
The Climatic Optimum 496
Medieval Climatic Fluctuations 497
The Little Ice Age 498
The Present and Future 498
Summary 499
Readings 501
Chapter 17
The Best of All Possible Worlds? 503
Three Important Maxims 504
Evolution of the Earth 504
The Idea of Evolution 504
Chemical Evolution of the Earth 505
Evolutionary Feedback 505
Our Place in the Global Ecosystem 506
Effects on Other Life 506
The Impending Ecological Crisis 507
Fouling of the Environment 507
Limits of the Earth’s Resources 512
Nonrenewable Resources 514
Energy—The Ultimate Limit 516
Alternative Futures 521
Summary—What Quality of Life? 522
Readings 524
Appendix I The Classification and Relationships of Living Organisms A-I
Appendix II English Equivalents of Metric Measures A-II
Glossary G-I
Index I-I