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Bellringer #24
• What is Geology?
• List four things that geologists study.
The Science of Geology
• The Greek geo means Earth and logos means
discourse.
• Geology is the science that pursues and
understanding of planet Earth.
Areas of Geology
• Geology is traditionally divided into two
broad areas
• Physical
• Historical
Physical Geology
• Physical geology- examines
the materials composing
Earth and seeks to
understand the many
processes that operate
beneath the surface.
Historical Geology
• The aim of historical geology, on the other
hand, is to understand the origin of Earth and
its development through time.
• It is trying to establish an orderly
chronological arrangement of the multitude of
physical and biological changes that have
occurred in the geologic past.
• Physical geology precedes the study of Earth
history because we must first understand how
Earth works before we attempt to unravel its past.
• To understand Earth is challenging because our
planet is a dynamic body with many interacting
parts and a complex history.
• Earth is constantly changing.
– Some of the changes are rapid and violent, as when
landslides or volcanic eruptions occur.
– Other changes are take place so slowly that it goes
unnoticed.
• A great deal of geology is based on observations
and experiments conducted in the field.
• Geology is also done in the laboratory where the
study of various Earth materials provides
information about many basic processes.
• Geology requires an understanding of knowledge
from physics, chemistry, and biology.
• Geology is a science that seeks to expand our
knowledge of the natural world and out place in
it.
Geology, People and the Environment
• Many issues studied in geology are of practical
value to people.
• Natural hazards are a part of living on Earth.
• Geologists study volcanoes, floods, earthquakes,
and landslides.
• These natural processes are only hazards when
people try to live where they occur.
Resources
• Resources are another important focus of geology.
• Resources include:
–
–
–
–
Water
Soil
Metallic and nonmetallic minerals
Energy
• Geology deals with the formation, maintaining of
supplies, environmental impact of their extraction
and use.
Human impact on the Environment
• Rapid world population.
– Gaining 100 million per year.
• Negative impact on natural flooding
• Clearing forests, building cities, and building dams
• Changes to the environment that were meant to
help society often has the opposite effect.
Historical Notes
• Aristotle believed that
rocks were created
under the “influence”
of the stars and that
earthquakes occurred
when air crowded into
the ground, was heated
by central fires, and
escaped explosively.
Catastrophism
• Mid-1600s
• James Ussher, Irish Archbishop
• Thought that Earth was only a few thousand years
old (4004 B.C.)
• His chronology (of human and Earth history) was
printed in the margins of the Bible.
• Catastrophists believed that Earth’s landscapes had
been shaped primarily by great catastrophes.
The Birth of Modern Geology
• Began in the late 1700s when
James Hutton, a Scottish physician
and farmer, published his Theory of
the Earth.
• Hutton put forth a principle that is
the pillar of geology today:
uniformitarianism
“The present
is the key to
the past.”
• Physical, chemical, and biological
laws that operate today have also
operated in the geologic past.
• The acceptance of
uniformitarianism meant the
acceptance of a very long history
for Earth.
• Earth’s processes may vary in
intensity but they still take a
very long time to be created or
destroyed.
• For example, mountains once existed in
portions of present-day Minnesota,
Wisconsin, and Michigan.
• Today this regions consists of low hills
and plains
• The rock record contains
evidence that shows Earth
has experienced many
cycles of mountain building
and erosion.
• The North American
continent is being lowered at
a rate of about 3 centimeters
per 100 years.
• It would take 100 million
years for water, wind, and
ice to lower mountains that
were 10,000 feet high.
Geologic Time
• Radioactivity was discovered in 1896
• Using it for dating was first attempted in 1905
• We know dinosaurs became extinct about 65
million years ago.
• The age of the Earth is about 4.6 billion years
Relative Dating and the Geologic Time Scale
• Relative dating- events are placed in their proper
sequence or order without knowing their age in
years.
• Law of superposition- in layers of sedimentary
rocks or lava flows, the youngest layer is on top
and the oldest is on the bottom.
• Sometimes the layers get
turned upside down. Then
the law does not work.
• The Grand Canyon is a good
example. The oldest rocks
are located in the inner
gorge and the youngest
rocks are found on the rim.
• So the law of superposition
establishes the sequence of
the rock layers but not their
numerical age.
Fossils
• Fossils are the remains of prehistoric life.
• Important in figuring out the geologic time scale.
• Principle of Fossil Succession- fossil organisms succeed
one another in order and therefore any time period can be
recognized by its fossil content.
• Without fossils, geologists lose their primary tool for
subdividing geologic time.
The Magnitude of Geologic Time
• For most of us something or someone who is 90
years old is very old and a 1000 year old artifact
is ancient.
• When you think about Earth’s 4.6 billion year
history, a geologic event that occurred 100
million years ago may be thought of as recent by
a geologist, and a rock sample that has been
dated at 10 million years may be called young.
Homework
• Define all of the vocab words for Chapter 21.
• A list of the words can be found on page 765
• Please number your vocab. There are 21
words.
• Due Friday!
Bellringer #25
• What are the three
physical
environments that
the Earth is divided
into?
The Earth as a System
•
A system is a group of interacting parts that form a
complex whole.
•
The Earth consists of rock, air, water and living things
that all interact with each other.
•
Scientists divided this system into four parts:
1. The Geosphere (rock)
2. The Atmosphere (air)
3. The Hydrosphere (water)
4. The Biosphere (living things)
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The Earth as a Integrated System
26
Atmosphere
• The atmosphere is the mixture of gases that
makes up the air we breathe.
• It is very thin.
• It is important:
– It provides the air we breath
– It protects us from UV radiation and heat
• Nearly all of these gases are found in the first
30 km above the Earth’s surface
Hydrosphere
• The hydrosphere makes up all of the
water on or near the Earth’s surface.
• The ocean covers 71% of Earth
• The ocean has a depth of 12,500 feet.
• The hydrosphere includes freshwater
found underground and in streams,
lakes, and glaciers.
•
Water is also found in the
atmosphere, on
land, and in the soil
Geosphere
• The geosphere is the mostly solid, rocky part
of the Earth that extends from the center of the
core to the surface of the crust
Biosphere
• The biosphere is the part of
the Earth where life exists.
• It extends from about 9km
above the Earth’s surface
down to the bottom of the
ocean.
• The biosphere is therefore
made up of parts of the
geosphere, the atmosphere,
and the hydrosphere.
Chapter 21 Planet Earth
Overview
• This chapter discusses:
– The composition of Earth’s interior
– The theory of plate tectonics
– The causes and classification of earthquakes and
volcanoes
– Types and properties of rocks and the rock cycle
– Physical weathering, chemical weathering, and
erosion.
S.1 Earth’s Interior and Plate Tectonics
• Focus
– Earth’s geological layers
– Plate tectonics
– Types of plate boundaries and structures that form at each
type
• Vocab
–
–
–
–
–
–
–
Crust
Mantle
Core
Lithosphere
Plate tectonics
Subduction
Fault
Key Ideas
〉How is Earth’s interior structured?
〉How has the appearance of Earth changed
over time?
〉What geologic features are common near
tectonic plate boundaries?
What is Earth’s Interior Like?
• We know that the Earth’s surface is solid
because we walk on it everyday.
• However, Earth is not solid all the way to the
center.
• Earth’s interior is made up of several distinct
compositional layers. (three)
• How do we know that?
Discovering Earth’s Interior
• Studying the Earth’s interior is not easy.
• The deepest well that has been drilled into
Earth’s interior is only about 12 km (7.7 miles)
deep.
– Kola Well in Russia 1970-1989
• An alternative method must be used to study
the interior of the Earth.
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Earth’s Interior

Scientists use seismic waves to learn about
Earth’s interior.

Seismic waves are the same waves that travel
through Earth’s interior during an earthquake.

A seismic wave is altered by the nature of the
material through which it travels.
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Earth’s Interior

Seismologists measure changes in the speed
and direction of seismic waves that penetrate
the interior of the planet.

With this technique seismologists have learned
that the Earth is made up of different layers
and have inferred what substances make up
each layer.
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Earth’s Interior
38
• Scientists divide the Earth into different
layers based on :
–Composition- what it is made of
–Physical Properties- any aspect of an
object or substance that can be measured
or perceived without changing its
identity
•
Earth is divided the into three major
layers:
– crust
– mantle
– core
39
Crust
• The crust is the thin and solid outermost layer
of Earth above the mantle.
• It is cooler than the interior of the Earth.
• It is made up of hard, solid rock.
• It is thin and makes up only about 1 % of the
Earth’s mass.
There are two kinds of crust
• Oceanic Crust
• Continental Crust
Oceanic Crust
• The crust beneath the ocean is called oceanic crust.
• It has an average thickness of 5 to 8 km (3.1 to 4.9
miles).
• Oceanic crust is the part of Earth's lithosphere that
surfaces in the ocean basins.
• Oceanic crust is primarily composed of mafic
rocks, or sima.
Mafic and sima what?
• Mafic is an adjective describing a silicate material
or rock that is rich in magnesium and iron.
• Sima is the name for the lower layer of the Earth's
crust. This layer is made of rocks rich in silicates
and magnesium minerals.
• Typically the sima when it comes to the surface is
basalt, called the 'basalt layer' of the crust or 'basal
crust' or 'basal layer' because it is the lowest layer of
the crust.
Age of oceanic crust. The red is most recent, and blue is the oldest.
The age of oceanic crust as of 1995. The red is the most
recent and blue is the oldest.
Oceanic Crust Composition
• Although a complete section of oceanic crust has not
yet been drilled, geologists have several pieces of
evidence that help them understand the ocean floor.
• Estimations of composition are based on analyses of
– ophiolites -sections of oceanic crust that are preserved on
the continents.
– comparisons of the seismic structure of the oceanic crust
with laboratory determinations of seismic velocities in
known rock types
– samples recovered from the ocean floor by submersibles
(midget submarines used by oceanographers), dredging,
and drilling.
• Oceanic crust is
significantly
simpler than
(
continental
crust
and generally
can be divided in
three layers.
Continental Crust
• The continental crust is the layer of granitic,
sedimentary and metamorphic rocks which
form the continents and the areas of shallow
seabed close to their shores, known as
continental shelves.
• Continental crust is thicker and less dense than
oceanic crust.
• Today continental crust is produced and
destroyed mostly by plate tectonic processes
The Crust – Earth’s Thin Skin
Relative to its size, Earth's crust
is about as thin as an apple's
skin.
This outermost layer is
composed primarily of two types
of rock.
The continental crust is mostly
granite.
The oceanic crust is mostly
basalt.
Mantle
• Mantle- the layer of rock
between the crust and core.
• Makes up 67% of the Earth’s
mass.
• 1,800 miles thick
• Composed of rocks of medium
density.
• The uppermost 100km of
the mantle is rigid. Along
with the crust, it makes up
the lithosphere (the
plates).
• The next layer, the
asthenosphere, is solid,
hot, and soft. It flows
much like a glacier does.
• The lower mantle is
extremely dense. It, too,
flows.
Mantle
Core
• Earth’s interior gets warmer with depth
• Earth’s core is nearly as hot as the surface of the sun.
• Core: the center part of the Earth below the mantle
• Made of the densest elements.
• 33% of the Earth’s mass
• Earth’s core is composed mainly of nickel and iron. It is
said to be the size of Mars.
• Radioactivity contributes to high internal
temperatures
– The breakdown of radioactive isotopes uranium,
thorium and potassium give off energy that
contributes to Earth’s high internal temperatures.
– Temperatures in the mantle can reach more than
1250° C.
– The core may reach temperatures above 5000° C.
Homework
• None
• Chapter 21 Vocab Due Tomorrow
Opening Activity
• Work with the people at your table
• Try to fit all of the cut out pieces
together to form one large landmass.
55
Layers of the Earth
1. lithosphere the solid, outer layer of the Earth
that consists of the crust and the rigid upper
part of the mantle.
•
It is a cool, rigid layer that is divided
into huge pieces called tectonic plates.
Layers of the Earth
2. asthenosphere the solid, plastic layer of the
mantle beneath the lithosphere.
a. It is made of mantle rock that flows
slowly, which allows tectonic plates to
move on top of it.
3. Mesosphere
- Beneath the asthenosphere is the
lower part of the mantle.
57
Layers of the Earth
4. Outer core is a dense liquid layer.
5. Inner core a dense, solid inner core, made up
mostly of iron and nickel.
•
Although the temperature of the inner core is
estimated to be between 4,000°C to 5,000°C, it
is solid because it is under enormous pressure.
58
Outer Core
Inner Core
• The outer core is
molten...and so hot it
could be as fluid as
water. Its motions
create Earth's
dynamic magnetic
field.
• The inner core is
under such immense
pressure that it is
solid metal.
Five layers of Earth
60
• Alfred Wegner was born in
Germany in 1880.
• Astronomy degree in 1905.
• A soldier in WWI. Developed
the theory of continental drift
while recovering from a war
injury.
• 1930, he went to Greenland to
help establish a weather station.
He took 4,000 pounds of
supplies. He froze to death on
the return journey. His theory
was supported 30 years after his
death.
Plate Tectonics
〉How has the appearance of Earth changed over
time?
〉Alfred Wegener hypothesized that all of the
continents might have been part of one landmass in
the past before they drifted apart.
– Wegener pieced the continents together like a puzzle and
called the supercontinent they formed Pangaea.
– Wegener found nearly identical fossils on widely separate
continents, which supported his idea.
Fossil Evidence
• Using fossil evidence,
Wegner showed that 200
million years ago, the
same kinds of animals
lived on continents that
are now oceans apart.
• He argued that animals
could not have evolved
on separate continents.
Mesosaurus bones
discovered in Sao Palo,
Brazil and western Africa.
Then
Now
Plate Tectonics, continued
• Evidence for Wegener’s ideas came later.
– Wegener’s theory of continental drift was ignored
until structures discovered on the ocean floor
provided evidence for a mechanism for the
movement of continents.
– Symmetrical bands on either side of a mid-ocean
ridge indicate that the two sides of the ridge were
moving away from each other and new ocean
floor was rising up between them.
Plate Tectonics, continued
• Alignment of oceanic rocks supports the
theory of moving plates.
– Iron in molten rock aligns itself with Earth’s
magnetic field as it cools.
– The Earth’s magnetic field reverses polarity about
every 200,000 years.
– The process is recorded as magnetic bands in rock,
based on the age of the rock.
– Symmetrical bands on either side of the Mid
Atlantic Ridge suggest that the crust was moving
away from the ridge.
Plate Tectonics, continued
• Earth has plates that move over the mantle.
– The crust and upper portion of the mantle are divided into
about seven large pieces called tectonic plates.
• lithosphere: the solid outer layer of Earth that consists
of the crust and the rigid upper part of the mantle
• plate tectonics: the theory that explains how large
pieces of the lithosphere, called plates, move and
change shape
Tectonic Plates
The major tectonic plates include:
1. The Pacific plate
2. North America plate
3. South America plate
4. Africa plate
5. Eurasian plate
6. Antarctic plates
7. Nazca Plate
8. Indian plate
9. Australian plate
69
Plate Tectonics, continued
• Scientists do not understand exactly what
makes tectonic plates move.
– One hypothesis suggests that plate movement
results from convection currents in the
asthenosphere, the hot, fluid portion of the mantle.
– Another hypothesis suggests that plate movement
results from the force of gravity acting on the
plates.
The diagrams
show the
break-up of the
super continent
Pangaea
(meaning
"all lands"
in Greek).
When Pangea existed,
there was a huge ocean
called Panthalassa.
pan- all, thalassa- sea
All that remains of
Panthalassa today is the
Pacific Ocean which
has been decreasing in
size ever since the
breakup of Pangea.
Homework
• Using your knowledge from the notes today,
answer the questions on the “Drilling into the
Earth” worksheet.
• Read the article “Inge Lehmann” and answer
the questions on the sheet of paper with the
questions.
Bellringer# 26
• List the three layers of the Earth and their
temperatures.
• Use your book! Chapter 21!
Plate Boundaries
• Lithospheric plates move and all major
interactions among the plates occur along their
boundaries.
– The border between two tectonic plates is called a
boundary.
• Volcanoes and earthquakes most often occur
where tectonic plates come together.
• At plate boundaries, many other dramatic
features, such as mountains and rift valleys, can
also occur.
Types of Plate Boundaries
• There are three different types of plate
boundaries.
• They are categorized by the type of plate
movement.
– Divergent plate boundaries
– Convergent plate boundaries
– Transform plate boundaries
Divergent plate boundaries
• A divergent plate
boundary occurs
where two plates
move apart and
create a gap
between them.
Divergent plate boundaries
• Hot rock rises from the asthenosphere and cools
to form new lithospheric rock.
• The two diverging plates pull the newly formed
lithosphere away from the gap.
• The drop in pressure causes the asthenosphere to
melt and form magma, which then forms new
oceanic crust. (new rock forms)
• Magma is liquid rock produced under Earth’s
surface.
Mid Oceanic Ridges
• Mid-oceanic ridges result from divergent
boundaries.
• Mid oceanic ridges are mountain ranges at
divergent boundaries in oceanic crust.
• Mountains on land are formed by the folding of
continental crust. Mid oceanic ridges are
created by magma rising to the Earth’s surface
and cooling.
• Rift valleys occur along the center of a mid-oceanic ridge.
• A rift valley is a narrow valley that forms where plates
separate.
• The most studied mid-oceanic ridge is the Mid-Atlantic Ridge.
• Most of it is under water but it can be seen on land in Iceland.
• New lithosphere is being added at the ocean
ridges
• So our planet should be getting larger
• Right?
Convergent plate boundaries
• The Earth’s total surface area remains constant.
• Older portions of the oceanic crust return to the mantle
along Convergent plate boundaries.
• Lithosphere is destroyed at convergent plate boundaries.
There are three types of
convergent plate boundaries
1. Oceanic plate collides with
a Continental plate
(EX: Andes Mountains)
2. Continental plate collides
with a Continental plate
(creates mountains
EX: Himalayas)
3. Oceanic plate collides
with a Oceanic plate
(island formation)
Subduction
Plates slide over each other at a convergent
boundary.
The area where one plate slides over another is
called a subduction zone.
Subduction zones produce ocean trenches,
mountains, and volcanoes.
• Subduction: the process by which one
lithospheric plate moves beneath another as a
result of tectonic forces
Oceanic trenches
• Form between two oceanic plates or an oceanic
plate and a continental plate.
• They can be very deep.
• The deepest is the Mariana Trench, located off the
coast of Asia in the Pacific Ocean.
• The deepest point is more than 6.8 miles beneath
the ocean surface.
"Grand Canyon of the Pacific", The
Marianas Trench is the world's
greatest ocean depth.
The island of Saipan rises more than 36,000
feet above the floor of
the trench.
In the Pacific there is always an association
between the arc of a
chain of islands and deep ocean trenches.
The southern islands are composed
predominantly of limestone while the
northern islands are composed of volcanic
rock.
The islands rise out of the sea in successive
level terraces indicative
of repeated volcanic elevations.
Subduction of oceanic crust generates volcanoes
Chains of volcanoes form on the upper plate in a subduction zone.
These volcanoes can form far inland from their associated oceanic
trench.
Magma cools and over time the accumulation of rock forms
chains of mountains and plateaus.
Islands may form where two oceanic plates meet
• When two oceanic plates meet:
– The denser plate sinks beneath the less dense plate.
– This forms a deep ocean trench
– Magma is formed and rises to the surface to form a
island arc.
– An island arc is a chain of volcanic islands.
• Ex: Islands of Japan form an island arc
• Formed because of the subduction of the Pacific plate.
Colliding tectonic plates create mountains
• The Himalayas are the largest mountain range
in the world.
• The Indian plate and the Eurasian plate
collided to form the mountains.
• They are growing in both width and height.
• The mountains grow several centimeters a year
because the plates move slowly.
• Mount Everest- tallest mountain with a peak at
29,035 ft above sea level.
Transform Fault Boundaries
• Plate movement can
cause breaks in the
lithosphere.
• Fault- a break in a body
of rock along which one
block slides relative to
another.
• Faults can occur
anywhere forces are great
enough to break rock.
• When rock moves horizontally at faults along
plate boundaries, the boundary is called a
transform fault boundary.
• Plate movement at these boundaries causes
earthquakes.
• San Andreas Fault- runs from Mexico through
California and out to sea north of San Francisco.
• These boundaries can occur on land or on the
ocean floor.
Types of faults
• There are four types of faults, each corresponding to
the stress state that produces it.
Reverse faults
• Reverse faults are caused by compresional stresses,
and are often found at convergent plate boundaries.
Reverse faults are caused by compresional
stresses, and are often found at convergent
plate boundaries.
Normal faults
• Normal faults
are caused by
tension or
extension and
are often found
at divergent
boundaries
Strike-slip faults
• Strike-slip
faults are
caused by
shear stress
and are often
found at
oblique-slip or
transform
boundaries.
Homework
• Section 1 Review page 737
• Complete # 1-8