Plate Tectonics and
Earth Structure
Lab 4
Concepts
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Internal Structure of the Earth
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Plate Tectonics
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Theory
Evidence of Continental Drift
Plate Movement
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3 components (core, mantle, crust)
Seismic tomography
Convergence
Divergence
Transform
Hot Spots
Internal Structure
3 main components
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Core
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Mantle
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Solid inner & liquid
outer
Thick layer of liquid hot
magma
Upper mantle & portion
of crust = lithosphere
Crust
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Oceanic (high density)
& continental (low
density)
Internal Structure
How do we know what’s inside the Earth?
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Seismic tomography
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Seismic waves (from earthquakes or underground tests) pass
through the earth and give us an idea of the types of
materials that make up the composition
Also, the waves help estimate how thick each layer is.
Plate Tectonics
Fact or Fiction?
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Theory: Earth’s crust is composed of numerous plates, which
move due to convection processes in the mantle.
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Idea developed in early 1900s, not taken seriously until 1960s.
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Alfred Wegener proposed the idea of “continental drift” in 1912.
Evidence of continental drift
1.
2.
3.
4.
5.
Convection Model (explains how plates move around)
“Puzzle”-like fit of continents
Fossil records
Geologic & Glacial records
Coal records
Plate Tectonics
Evidence of Continental Drift: Convection Model
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Earth’s core is hot, so heated
magma (near the core) rises
up to be closer to the crust,
where it can be cooled.
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Cooled magma then sinks
back to the core.
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Constant rotation of magma
makes plates move.
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The ways in which plates
move depend on the direction
of the rotation.
Tectonic Plates
Evidence of Continental Drift: “Puzzle”-like Fit of Continents
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200 million years ago: Pangaea (“all Earth”)
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Earliest landmass formed on Earth.
Was a mash-up of all the continents we know today.
Tectonic Plates
Evidence of Continental Drift: Fossil Records
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Example: Matching
fossil records of
reptiles have been
found in Africa and
South America
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Continents were so
close to each other
(or even joined) that
animal life could
easily travel to and
from them.
Similar fossil records
for vegetation found.
Tectonic Plates
Evidence of Continental Drift: Geologic & Glacial Records
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Similar rock strata
across continents
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Southwest Africa
matches up with
southeast South
America, etc.
Evidence of
glaciation in areas
that are not
necessarily
glaciated anymore
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e.g., Australia
Tectonic Plates
Evidence of Continental Drift: Coal Records
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Coal formation
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Wet and warm climates.
Millions of years for
biological material (e.g.,
plant and animal life) to
break down and form
coal.
Coal reserve found under
ice cap of Antarctica.
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Present in many areas of
Russia and northern
China, as well as
northern US and Canada.
Plate Movement
3 types of movement: Divergent, Convergent, and Transform
Plate Movement
Divergent Movement
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Plates move away from each other, often at mid-oceanic
ridges.
Result = trench with mountains to each side.
Red Sea and Great Rift
Valley, Africa
Plate Movement
Divergent Movement
Plate Movement
Convergent Movement, version 1
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Plates of the same composition (oceanic vs. oceanic or
continental vs. continental) move towards each other.
Result = mountain chain.
Indian and Eurasian
plates come together.
Form the Himalayas.
Plate Movement
Convergent Movement, version 2
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Occurs when a heavier oceanic plate comes into contact
with a lighter continental plate. The continental plate is more
buoyant, and will rise above the oceanic plate.
The oceanic plate is “subducted” under the continental one.
Result = volcanic mountain chain.
The heavier Nazca plate
subducts under the lighter
South American plate.
Forms Andes Mountains.
Plate Movement
Transform Movement
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Plates slip past each other (parallel motion).
Often, the force created by the parallel motion is what sets
off earthquakes.
Pacific plate moves NW, North American
plate moves SE. San Andreas fault, CA.
Hot Spots
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Caused by a mantle plume
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Does not necessarily occur on plate boundaries.
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A narrow stream of magma rises up from the mantle and
breaks through the crust.
Example: in middle of ocean  Hawai’i
Example: in middle of continent Yellowstone
Hot spots are stationary
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It is the plates moving over them
that creates a series of volcanic
formations
Movement away from the hot spot
indicates older landforms (further
away from active hot spot, the
older it is).
Hot Spots
Where are they located?
Notice that they are not necessarily on plate boundaries!
Hot spots can happen anywhere.
Hot Spots
Hawai’i: X marks the [active hot] spot
x
“X” marks the current location of the Hawai’ian hot spot. It is creating a
new landform, “Lo’ihi”, which is still 3,200 feet below the water surface.