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Geology
GEOLOGIC PROCESSES
‣ The earth is made up of a core, mantle, and crust and
is constantly changing as a result of processes taking
place on and below its surface.
‣ The earth’s interior consists of:
‣ Core: innermost zone with solid inner core and
molten outer core that is extremely hot.
‣ Mantle: solid rock with a rigid outer part
(asthenosphere) that is melted pliable rock.
‣ Crust: Outermost zone which underlies the
continents.
GEOLOGIC PROCESSES
 Major features of the earth’s crust and upper mantle.
Figure 15-2
The Earth’s Crust
‣ The Earth’s crust is relatively thin relative to the rest of the
planet.
25-70 km thick below the continents
around 10 km thick below the oceans.
‣ The crust is rich in oxygen and other lighter minerals such as
silicon, calcium and aluminum and is less dense than the
mantle. The crust rides over the mantle causing the formation of
oceans, mountains and volcanoes.
Oceanic crust
Lithosphere
Continental crust
The continental crust is made
up of igneous, metamorphic, and
sedimentary rocks. It is not
recycled within the Earth as often
as oceanic crust, so some
continental rocks are up to 4
billion years old.
Asthenosphere
More than two thirds of the Earth’s surface is
composed of oceanic crust. Oceanic crust is
continually formed from mantle material and so is
relatively young. Even the oldest parts of the ocean
floor are no more than 200 million years old.
The Earth’s Crust
Sediments eroded from continents and
compressed into sedimentary rock can
be later lifted and exposed in mountains
Igneous rocks, such as basalt, form a
major component of the crust and are
essentially unchanged since their formation.
Water, as rain, drains to rivers and
lakes, which flow back to the ocean
eroding the landscape in the process.
The Earth's persistent oceans of liquid
water cycle moisture through the
atmosphere to the land and back again.
The Lithosphere
‣ The lithosphere
comprises the crust
and the upper most
region of the mantle.
‣ The lithosphere
carries the outer rock
layer of the Earth,
which is broken up
into seven large,
continent-sized
tectonic plates and
about a dozen
smaller plates
‣ The lithosphere
overlies the hotter,
more fluid lower part
of the mantle, the
asthenosphere.
Continental
Crust
Oceanic
Crust
Mohorovicic
discontinuity
Lithosphere
Approx. 70km
Asthenosphere
Approx. 250km
Mantle
Abundant Elements on
Earth
‣ Oxygen - most abundant element in
Earth’s crust.
‣ Nitrogen - most abundant element in the
Earth’s atmosphere.
‣ Iron - most abundant element in the
Earth’s core.
‣ Aluminum - element commercially
extracted from bauxite
GEOLOGIC PROCESSES
‣ Huge volumes of heated and molten rack
moving around the earth’s interior form
massive solid plates that move extremely
slowly across the earth’s surface.
‣ Tectonic plates: huge rigid plates that
are moved with convection cells or
currents by floating on magma or
molten rock.
Spreading
center
Collision between
two continents
Subduction
zone
Continental
crust
Oceanic
crust
Ocean
trench
Oceanic
crust
Continental
crust
Material cools Cold dense
as it reaches material falls
the outer back through
mantle
mantle
Hot
Mantle
material
convection
rising
cell
through
the
mantle
Two plates move
towards each other.
One is subducted
back into the mantle
on a falling convection
current.
Mantle
Hot outer
core Inner
core
Fig. 15-3, p. 337
The Earth’s Major Tectonic
Plates
Figure 15-4
The Earth’s Major Tectonic
Plates
The extremely slow movements of these plates cause them to grind
into one another at convergent plate boundaries, move apart at
divergent plate boundaries and slide past at transform plate
boundaries.
Figure 15-4
Fig. 15-4, p. 338
Plate Boundaries
‣ Throughout geological time, the tectonic plates have moved
about the Earth's surface, shuffling continents, opening and
closing oceans, and building mountains.
‣ The evidence for past plate movements has come from several
sources:
mapping of plate boundaries,
the discovery of sea floor spreading,
measurement of the direction and rate of plate movement,
the distribution of ancient mountain chains, unusual deposits,
and fossils
Continental crust
Oceanic crust
Mid-ocean ridge
Hot spot
Subduction zone
Importance of Plates
‣Plate movement adds new land at
boundaries, produces mountains,
trenches, earthquakes and volcanoes.
‣The Pacific plate is off the coast of
California. Lots of volcanoes and
earthquakes occur here.
‣ It is the largest plate and the location of
the ring of fire.
Plate Movement
‣ Heat from the mantle drives two kinds of asthenospheric
movement:
convection
mantle plumes
‣ Plate motion is also partly driven by the weight of cold, dense
plates sinking into the mantle at trenches.
‣ This heavier, cooler material sinking under the influence of
gravity displaces heated material that rises as mantle plumes.
Crust cools and sinks into mantle
under the influence of gravity
New crust created
at spreading ridge
Mantle plume of
hotter material rising
from near the core
Crust melts as it
descends into mantle
IRON-NICKEL
CORE
Heating and
cooling causes
convection
Sea floor Spreading
‣ Sea floor spreading occurs as magma wells up from
the mantle below, forcing the plates apart.
‣ As the new rock cools and solidifies it picks up and
preserves the direction of the Earth’s magnetic field.
New rock on either side of the ridge
has the same magnetic information.
On average the Earth’s magnetic field
reverses once every million years. This
leaves magnetic bands in the crust.
This shows clear evidence of sea floor
spreading and plates tectonics.
Divergent Plates
‣ The size of the plates is constantly changing, with some
expanding and some getting smaller.
‣ These changes occur along plate boundaries, which are marked
by well-defined zones of seismic and volcanic activity.
‣ Plate growth occurs at divergent boundaries along sea floor
spreading ridges such as the Mid-Atlantic Ridge and the Red
Sea.
Divergent plate boundary
Continental rift zone
Magma upwellings through
fractures cause plates to diverge.
The changing convection currents inside
the Earth can cause new boundaries to
form and old ones to disappear.
Convergent Plates
‣ Plate attrition occurs at convergent boundaries
marked by deep ocean trenches and subduction
zones. The Pacific plate is a convergent plate.
Convergent plate boundary
Divergent plate boundary
Deep sea trench
Mountain range
Active
volcano
When an oceanic plate collides with a
continental plate, it sinks in to the
mantle and eventually melts.
Oceanic crust
Continental crust
Subducting plate
Mantle
Plate Boundaries
‣ The
Earth’s major earthquake
and volcanic zones occur
along plate boundaries.
‣ The
movements of plates puts
crustal rocks under strain.
‣ Faults
are created where rocks
fracture and slip past each
other.
‣ Earthquakes
are caused by the
energy released during rapid
slippage along faults.
New Zealand’s alpine fault is visible
from space, marking a transform
boundary between the Indo-Australian
plate and the Pacific plate.
Continental
Boundaries
‣ Where
continental
plates meet, the land
may buckle and fold
into mountain
ranges.
‣ The
highest mountains
on Earth, the
Himalayas, were
formed in this way as
the subcontinent of
India collided with
continental Asia.
‣ Few
volcanoes form in
these areas because
the continental crust is
so thick.
Transform
Boundaries
Image: NASA
‣ Plates may slide past
each other at transform
boundaries
‣ Plate size is not affected
because there is no
construction or
destruction of material at
these boundaries.
However, they are
responsible for large
earthquakes.
‣ Pressure from the plates
causes the boundary to
lock in position and
earthquakes occur when
the rock gives way to
release the pressure.
San Andreas fault
Photo: Wiki commons
Faultline movement after an earthquake
Transform Boundary
California will not fall into the ocean!
The Rock Cycle
‣ The
Rock Cycle is the interaction of processes
that change rocks from one type to another.
‣ The
Earth's rocks are grouped together
according to the way they formed as:
igneous
metamorphic
sedimentary rocks
‣ Igneous
rocks are created by volcanism and
may form above the surface as volcanic rocks
or below the surface as plutonic rocks.
‣ Heat
and pressure within the Earth can
transform pre-existing rocks to form
metamorphic rocks.
‣ When
rocks are exposed at the surface, they
are subjected to weathering and erosion and
form sediments.
Types of Rock
‣ The Earth's crust is made up of solid, naturally
occurring assemblages of minerals called rocks.
‣ The huge diversity of the Earth's rocks has developed
over thousands of millions of years through:
igneous activity (volcanism)
metamorphism (changes in form)
sedimentation (formation of sediments and
sedimentary rocks)
Igneous rocks
Metamorphic rocks
Sedimentary rocks
All 3 rocks are recycled and converted into all classes
Types of Rock
Obsidian
‣
Igneous rocks solidify from
volcanic magma They vary in
composition from basalt to
granite and in texture from
rapidly cooled glasses, such
as obsidian, to slowly cooled
coarse grains, such as
granite.
Granite
Marble
‣
Metamorphic rocks result when
pre-existing rock is transformed
by heat and pressure.
Metamorphic rocks are classified
by texture and composition.
Examples include gneiss, slate,
marble and schist.
Schist
Conglomerate
‣
Sedimentary rocks form when
sediments accumulate in
different depositional
environments and then become
compressed into brittle, layered
rocks, e.g. shale, sandstone,
limestone, and conglomerate.
Sandstone
Rock Classification
‣Igneous - forms the bulk of the earth’s
crust. It is the main source of many nonfuel mineral resources.
‣ Intrusive Igneous Rocks – formed from
the solidification of magma below ground
‣ Extrusive Igneous Rocks – formed from
the solidification of lava above ground
‣ Examples – Granite, Pumice, Basalt,
Diamond, Tourmaline, Garnet, Ruby,
Sapphire
Sedimentary
‣Rock formed from sediments.
Most form
when rocks are weathered and eroded into
small pieces, transported, and deposited in
a body of surface water.
 Clastic – pieces that are cemented
together by quartz and calcium carbonate
(Calcite).

Examples: sandstone (sand stuck together),
Conglomerate (rounded & concrete-looking)
and Breccia (like conglomerate but w/
angular pieces)
Sedimentary (Continued)
‣Nonclastic –
‣ Chemical Precipitates – limestone
precipitates out and oozes to the
bottom of the ocean (this is why there
is a lot of limestone in S.A.)
‣ Biochemical Sediments – like peat &
coal
‣ Petrified wood & opalized wood
Metamorphic
‣Description – when preexisting rock is
subjected to high temperatures (which
may cause it to partially melt), high
pressures, chemically active fluids, or a
combination of these
‣Location – deep within the earth
Examples of Metamorphism:
‣Contact Metamorphism- rock that is
next to a body of magma
 Ex.
limestone under heat becomes
marble through crystallization
 Limestone -> marble
sandstone -> quartzite
shale -> hornfelds (slate)

Dynamic Metamorphism – earth movement
crushes & breaks rocks along a fault. Rocks
may be brittle- (rock and mineral grains are
broken and crushed) or it may be ductile(plastic behavior occurs.)

Rocks formed along fault zones are called
mylonites.
Metamorphic (Continued)
‣ Regional Metamorphism – during mountain

building; great quantities of rock are subject to
intense stresses and heat. Ex. cont. shelves ram
together
Progressive Metamorphism – One form of rock
changing into another

shale->slate->schist->gneiss

coal->graphite

granite->gneiss
Rock Dynamics
Fine grained
(volcanic)
Course grained
(plutonic)
Mineral content
Silica content
Fluidity
pH
*Mafic minerals contain magnesium, iron, and heavy elements. They are usually dark in color.
Felsic minerals contain lighter elements such as silicon, oxygen, and aluminum. They are usually light in color.
Extrusive
igneous rock
weathering, exposure, and
transport, followed by burial
The rock cycle constantly redistributes material
within and at the Earth's surface over millions
of
years
by
melting,
erosion,
and
metamorphism. It is the slowest of the Earth's
cycles and is responsible for concentrating the
mineral resources on which humans depend.
LAND
cooling and
crystallization
SEA
CRUST
uplift and
erosion
Intrusive
igneous rock
uplift and
erosion
burial and
recrystallization
cooling and
crystallization
MANTLE
deep burial
burial and
recrystallization
Magma
melting
Sedimentary
rock
Metamorphic
rock
deep burial
metamorphic rock
metamorphic rock
ROCKS FORMED AT THE EARTH'S SURFACE ROCKS FORMED IN THE EARTH'S INTERIOR
SURFACE
The Rock Cycle
Steps
Rock Cycle
Geologic Time
‣ Precambrian Era– oldest and largest division of
geologic time (87% of Earth’s history)
‣
‣
Time Frame – 4600 to 544 million years ago
Organisms –
‣
oldest definite fossils known
‣
prokaryotes (lacking a cell membrane), Similar to
cyanobacteria; (oxygen-producing & underwent
photosynthesis)
‣
It was 2 billion years later before the origin of
eukaryotes
‣
By the end of this era we had the origin of shell-less
Paleozoic Era
‣ Time Frame – 544 to 245 million years ago
‣ Periods – (from oldest) Cambrian, Ordovician, Silurian, Devonian,
Carboniferous, Permian
‣ Organisms – (referred to as the explosion of life)
‣
‣
‣
‣
At the beginning was the origin of most invertebrates
Then the first vertebrates & first land plants appeared
Around the middle of this era the first amphibians and insects
appeared
During the second half of this era the first reptiles appeared.
Mesozoic
‣ Time Frame – 245 to 66 million years ago
‣ Periods – Triassic, Jurassic, and Cretaceous
‣ Age of Dinosaurs or Reptiles
‣ Organisms –
‣
‣
‣
During Triassic the first mammals & dinosaurs
appeared
Jurassic-dinosaurs become dominant
Cretaceous- mammals began to spread out and
flowering plants appeared & the dinosaurs became
Cenozoic
‣Time Frame – 66 million years ago
to the present.
‣Age of Mammals.
‣Periods –
‣ Tertiary – Paleocene, Iocene,
Oligocene, Miocene, Pilocene
‣ Quaternary – Pleistocene, Recent
Evidence - fossils
‣Relative Dating – The age of a fossil
in terms of other fossils around it.
Fossils in layers of sedimentary
rocks, younger are on top & older
are in the lower layers.
‣ Index Fossils – are used to coordinate
the fossils at one location with those at
another. For ex. One island with
another
Evidence Cont.
‣Absolute Dating – age is given
in years instead of relative
terms
‣ Ex. Radioactive Dating –
determines the age of fossils by
looking at the isotopes of
elements that accumulate with
the organisms when they were
alive
Fossil Record
‣ Fossils are mineralized or petrified replicas of
skeletons, bones, teeth, shells, leaves and seeds
or impressions of such items; usually found in
sedimentary rock.
‣ Organisms had to die on the right place and right
time for burial conditions to favor fossilization
‣ Rock must be exposed for us to see
‣ The fossil record is incomplete because of this.
‣
‣
‣
‣
‣
Fossil Types
Remainders – the actual body or parts of an
organism
Petrified – the bone has been replaced by mineral
Molds – bone gets buried and the sediment turns
into rock, and the animal is dissolved away
Casts – if another mineral fills the mold and hardens
in the shape of the old animal it becomes a cast
Tracks – footprints left in the sediment that solidifies
‣
Ex. dinosaur tracks in Texas
Types continue
‣ Carbonization – if an animal dies and the
sediment crushes the animals as fossilization is
occurring, you will have a thin black coating on
the fossil. Much of this is coal.
‣ Impression – (trace fossil) there is an impression
of the fossil, but the fossil is gone
‣ Amber – resin from certain trees that small
insects and other organisms get trapped in
Types Continued
‣Burrows – an animal like a worm burrows
into the mud, then the burrow becomes
fossilized
‣Coprolites – fossil excrement (poop) can
sometimes give definitive knowledge about
the eating habits of the animals
‣Gastroliths – smooth, polished stones that
are found in the abdominal cavities of the
skeletons of dinosaurs. They are thought
to have helped the huge animals grind up
vegetation in their stomachs.
Fossil Record
‣Ideal Conditions – quick burial and the
presence of some hard parts
‣Meaning – tells us the date of the organism
by dating the rock. You can tell what came
before what by superposition; mass
extinctions; pop. explosions.
‣ Support for Evolution – changes over time
can be seen. i.e. Transitional fossils