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Ch. 7 Plate Tectonics
This is a satellite image of the San Francisco Bay area. The row of lakes below marks the
line of the San Andreas fault, a crack in Earth's crust.
7.1 Inside the Earth
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Discover Activity
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Canisters with different
items
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What is inside?
Can you dig down to the
center?
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The deepest mine in
the world, a gold mine
in South Africa,
reaches a depth of
3.8 kilometers. But it
only scratches the
surface.
Finding Indirect Evidence
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Geologist use an
indirect method of
studying Earth’s
interior.
Hanging a picture on
a wall
Geologists use
seismic waves.
Finding Indirect Evidence
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Seismic waves - A
vibration that travels
through Earth
carrying the energy
released during an
earthquake.
Finding Indirect Evidence
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Geologists record the seismic waves and study
how they travel through Earth.
The speed of these seismic waves and the paths
they take reveal how the planet is put together.
Using data from seismic waves, geologists have
learned that Earth's interior is made up of
several layers.
Each layer surrounds the layers beneath it,
much like the layers of an onion.
A Journey to the Center of the
Earth
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Book written in 1864
Scientists knew
nothing.
Was the Earth hot,
cold, solid, or hollow?
A Journey to the Center of the
Earth
A Journey to the Center of the
Earth
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You would need a vehicle that could travel
through solid rock.
The vehicle would carry scientific
instruments to record changes in
temperature and pressure as you descend
toward the center of Earth.
Temperature
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As you start to tunnel beneath the surface, you
might expect the rock around you to be cool. At
first, the surrounding rock is cool.
Then at about 20 meters down, your instruments
report that the surrounding rock is getting
warmer. For every 40 meters that you descend
from that point, the temperature rises 1 Celsius
degree. This rapid rise in temperature continues
for several kilometers. After that, the
temperature increases more slowly, but steadily.
Pressure
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During your journey to the center of Earth,
your instruments also record an increase
in pressure in the surrounding rock. The
deeper you go, the greater the pressure.
Pressure is the force pushing on a
surface or area. Because of the weight of
the rock above, pressure inside Earth
increases as you go deeper.
A Journey to the Center of the
Earth
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Three main layers
make up Earth's
interior: the crust,
the mantle, and the
core. Each layer has
its own conditions
and materials.
The Crust
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The crust is a layer of
rock that forms Earth's
outer skin. On the crust
you find rocks and
mountains. But the
crust also includes the
soil and water that
cover large parts of
Earth's surface.
The Crust
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The crust is the dry
land and the ocean
floor.
It is very thin like an
onion.
Thinnest under the
ocean and thickest
under the mountains.
5-40 km thick
The Crust
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Oceanic crust is made up
of mostly of basalt (A).
Basalt is dark, dense, and
fine texture.
Continental crust is
mainly made up of granite
(B). Granite forms
continents, less dense,
large crystals, light
colored, and coarse
grained.
The Mantle
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The next layer is the
mantle, a solid made
of hot rock.
The uppermost part of
the mantle is the
lithosphere. “Litho”
means stone and is
about 100 km thick.
The Mantle
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The largest part of the
mantle is the
asthenosphere. It is
hotter and under
increasing pressure. It is
a soft and bendable like
plastic.
Asthenes means weak.
But this layer is far from
weak. It can flow slowly.
The mantle is approx.
3,000 km thick.
The Core
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The Earth’s core
consists of two parts a liquid outer core
and a solid inner core.
Iron and nickel
(metals) make up
both parts of the core.
The Core
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The outer core is a layer
of molten metal that
surrounds the inner core
and behaves like a thick
liquid.
The inner core is a
dense ball of solid metal.
In the inner core, extreme
pressure squeezes the
atoms of iron and nickel
so much that they cannot
spread out and become
liquid.
The Core
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The outer and inner
cores make up about
one third of Earth's
mass, but only 15
percent of its volume.
The inner and outer
cores together are just
slightly smaller than the
moon.
Temperatures range
between 2000 -5000
which is as hot as the
sun’s surface.
Earth’s Magnetic Field
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Currents in the liquid outer
core force the solid inner
core to spin at a slightly
faster rate than the rest of
the planet.
These currents in the outer
core also create Earth's
magnetic field, which
causes the planet to act like
a giant bar magnet.
Earth’s Magnetic Field
Tectonic Plates
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Tectonic plates are pieces of the
lithosphere that move around of top of the
asthenosphere.
The lithosphere is like a jigsaw puzzle.
A Giant Jigsaw Puzzle
Comparing plates
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Cocos plate vs. South American plate
A Tectonic Plate Close-Up
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Figure 5
Like Ice Cubes in a Bowl of
Punch
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Ice cubes floating in a bowl.
Tectonic plates “float” on the
asthenosphere in a similar way.
Mapping the Earth’s Interior
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Seismic waves
Seismographs