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Earth’s Interior
6C
Indirect Evidence
 We have never seen
deep inside the Earth.
 Geologists use an
indirect method that
relies on inferring what
might be below the
surface.
 Using data from seismic
waves, astronomy, and
other sources, scientists
have learned the Earth
is made of layers.
Temperature
 A measure of how fast the
particles of a substance
are moving.
 At first, the Earth gets a
little cooler as you go
deeper.
 But at 20 meters depth,
the temperature starts
rising.
 For every 40 meters you
descend, the temperature
rises about 1° Celsius.
After a few kilometers this
rate slows a bit, but it gets
hotter the deeper you
travel inside the Earth.
Pressure
 Is the force pushing on
a certain area.
 The deeper you go, the
more rocks are above
you. The more rocks
there are, the more they
weigh.
 So the deeper you go,
the greater the pressure
pushing on you.
The Earth’s Layers
Why Does the
Earth have Layers?
 When the Earth formed, it
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was molten rock.
As the Earth cooled, the
denser materials (Fe and
Ni) sank to the core.
The earth’s rotation flung
the lighter elements
towards the surface.
So the earth layers are
caused by density.
This process is called
differentiation.
Crust
 Forms the Earth’s outer skin.
 Very thin layer.
 If the Earth were an onion, this layer would be like the
paper thin skin of the onion.
 Oceanic crust: thinnest, made of dense basalt.
 Continental crust is thickest, made of less dense
granite.
The Mantle
 Layer below the crust
 Solid
 Very hot rock
 Pressure and
temperature increase
as we go deeper.
 Upper mantle is divided
into two parts, the
lithosphere and the
asthenosphere.
Lithosphere
 Lithosphere is the upper
part of the mantle and
the crust.
 Litho means stone in
Greek.
 The crust and upper
part of the mantle are
very similar, so they are
combined in this layer.
 The lithosphere actually
floats on top of the soft
rock below it.
Asthenosphere
 Upper mantle, right below the lithosphere
 In Greek, asthenes means “weak.”
 Less rigid than the layers above.
 Rock is hot and soft, like road tar on a hot summer
day.
 This material actually flows slowly.
The Core
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Has two parts:
Liquid outer core
Solid inner core
Both made of nickel (Ni)
and iron (Fe)
 Outer is a liquid molten
metal
 Inner core is a solid
metal
 Liquid outer core
causes the Earth to
have a magnetic field
Earth’s Magnetic Field
 Spinning outer core
produces a magnetic
field
 Causes planet to be like
a large bar magnet
 Compasses will point to
the Earth’s magnetic
pole, not the geographic
pole
 This magnetic field
helps protect the Earth
from harmful radiation
from space