The Earth’s Layers and Plate Tectonics
Study Guide #1 Unit 3
The Earth’s Layers
Four main layers
The crust
Mantle (upper and Lower)
The outer core
The inner core
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The Crust
Thin layer-surface of the Earth
composed of two basic rock types:
granite =Continental Crust
basalt =Oceanic Crust
Separated from the Mantle by the Mohorovicic discontinuity MOHO
broken into many pieces called plates
plates "float" on the soft, plastic mantle
Continental plates sit on top of the much denser Oceanic Plates
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The Mantle
Located below the crust
 Thickest Layer of the Earth
Upper Mantle
Directly below the crust
Upper most part is part of the Lithosphere
Lower most upper mantle is flowing and part of the Asthenosphere
Lower Mantle
Semi-rigid
Lithosphere
crust and the uppermost layer of the mantle together make up a zone of rigid, brittle
rock called the Lithosphere
Asthenosphere
layer below the rigid lithosphere
is a zone of asphalt-like consistency
part of the mantle that flows and moves the plates of the Earth
Site in which convection currents are found
Convection Currents
caused by the very hot material at the deepest part of the mantle rising, then cooling,
sinking again and then heating, rising and repeating the cycle over and over
crust gets a free ride with these currents
Outer Core
Liquid nickel and iron
4000 degrees F to 9000 degrees F
Inner Core
Solid nickel and iron
may reach 9000 degrees F
Acts like a solid because of the extreme pressures
Plate tectonics
science that studies how the parts of the crust move
The Earth's crust is broken into many pieces called plates
12 main plates on the Earth's surface
Continental Drift
1912 Alfred Wegener, German meteorologist, introduced the Continental Drift
Theory
states: that the continents have moved and are still moving today.
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Support for Continental Drift Theory
Continents seemed to fit together like puzzle pieces
He found similar fossils on continents that are thousands of miles away from
each other
•similar sequence of rocks at numerous locations
•plant fossils found in Antarctica which suggested that Antarctica was once a
warmer continent
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Pangaea
250 millions years ago the Earth's seven continents were all grouped together into a
super continent
Problems with Wegner’s Theory
 No one believed his theory because he had no way to explain how the continents
moved
Arthur Holmes
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Suggested the theory of convection currents to explain how the continents moved
around the Earth’s surface.
Plate Boundaries
plate boundary : where two plates come together
3 kinds of plate boundaries
Convergent boundary
Convergent boundary -where crust is destroyed as one plate dives under another
collide to form mountains or a subduction zone.
Divergent boundary
Divergent boundary -where new crust is generated as the plates pull away from each
other
Mid-Atlantic Ridge
 splits nearly the entire Atlantic Ocean north to south
 Probably the best-known and most-studied example of a divergent-plate
boundary.
 Sea-floor Spreading-as the magma rises the older sea floor spreads apart to make
room for the new sea floor
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Harry Hess-1960-from Princeton University
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Proposed that hot, less dense material rises toward the Earth’s crust at the midocean ranges
Transform boundary
Transform boundary -where crust is neither produced nor destroyed as the plates slide
horizontally past each other