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6.1 Earth’s Structure
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Fossils of the same plants and
animals are found on different
continents that are separated by
wide oceans. How could this have
happened and what does this
suggest about the continents?
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Compositional Layers of Earth
Core
Earth’s dense, metallic center made up
mainly of metal iron
Mantle
Dense, thick middle layer
Crust
The surface layer composed mostly of
silicon, oxygen, and aluminum.
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Layers of the Earth
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tectonics\The_Four_Layers_of_the_Earth_s_Interior__Inner_Core__Outer_C
ore__Mantle__and_Crust.asf
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Describe Earth’s compositional layers.
The crust, Earth’s surface layer, is rocky,
thin, fractured, and composed mostly of
silicon and oxygen. The mantle, Earth’s
middle layer, is thick, dense, and rich in
iron and magnesium. The core, Earth’s
innermost layer, is dense and composed
mostly of iron.
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Two types of crust
Continental crust
•Thicker than oceanic crust
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Oceanic Crust
•Has almost twice as much iron, calcium, and
magnesium than continental crust
•More dense and heavier than continental
crust
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Physical Structure of Earth
Lithosphere
•A cool, rigid layer that includes the crust
and the upper part of the mantle.
•Divided into pieces called tectonic plates.
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Asthenosphere
•Below the
lithosphere, a layer
of the mantle that
is made of very
slow-flowing solid
rock
•Tectonic plates
move
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Mesosphere
•Below the asthenosphere
• The lower part of the mantle.
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Outer core
•A layer of liquid iron and nickel
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Inner core
•Made mostly of iron and nickel
•Very hot, but it is solid because of extreme
pressure
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Continental Drift
•A single large landmass broke up into smaller
landmasses to form the continents which then drifted to
their present locations.
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Evidence for Continental Drift:
•Fossils of the same plant and animal species
are found on continents that are far from
each other
•The location of mountain ranges and of
similar types of rock.
•Ancient climatic zones supports this idea.
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List three lines of evidence for
continental drift.
Three lines of evidence that support
continental drift are the fit of the
continents, the existence of the same
fossils on different continents, and the
locations of mountain ranges and
similar types of rocks on different
continents.
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Alfred Wegener
Wrote about continental drift
•Pangaea – the single large continent that gave
rise to today’s continents.
•Pangaea existed 245 million years ago.
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pangea.gif
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Continental Drift
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Briefly describe the movement of the continents
over the past 245 million years.
Beginning 245 million years ago, all of the present
continents were joined in a single landmass called
Pangaea. Approximately 135 million years ago,
Pangaea split into a huge northern continent called
Lauasia and a huge southern continent called
Gonwanaland. By 65 million years ago they split
into the continents we know today. Over the past
65 million years, the continents have moved slowly
to their present positions.
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Sea-Floor Spreading
•Mid-ocean ridges are underwater mountain chains
that run through Earth’s ocean floor.
•There are patterns of magnetism in the sea-floor
rocks.
•Magnetic reversal - the process by which Earth’s
magnetic poles change places.
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Sea-Floor Spreading
• At the mid-ocean
•
ridge, magma rises
through fractures in
the sea floor.
Magma cools, and
new rock forms.
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Sea Floor Spreading
•When new rock forms, the older rock
gets pulled away from the mid-ocean
ridge.
•This process which new sea floor forms
as old sea floor is pulled away is sea-floor
spreading.
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Sea Floor Spreading
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Review Questions
1. List the layers of Earth by their chemical
composition and by their physical properties.
The composition layers of Earth, beginning at
Earth’s surface, are the crust, mantle, and core.
They physical layers of Earth, beginning at Earth’s
surface, are the lithosphere, asthenosphere,
mesosphere, outer core, and inner core.
2. Describe evidence that supports the existence of
Pangaea.
The fit of the continents, the existence of the same
fossils on different continents, and the locations of
mountain ranges and similar types of rock on
different continents support the existence of
Pangaea.
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3. Explain the process by which new sea floor forms
at mid-ocean ridges.
At mid-ocean ridges, magma rises through a
series of fractures to the ocean floor. The magma
cools and forms new rock. As this new rock forms,
older rock is pushed away from the mid-ocean
ridge.
4. If rocks found in North America and rocks found in
Europe are the same, what does this indicate
about the North American and European
continents?
This evidence would indicate that North America
and Europe were once joined.
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Review 6.1 Quiz
•Continental drift
•Core
•Magnetic reversal
•Mantle
•Chemical make-up
•Crust
of each layer
•Lithosphere
•Asthenosphere
•Fossils
•Seismic waves
•Sea floor spreading
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