Earth’s Interior
The best way to find out what’s inside Earth might
be to dig a tunnel to its center—but that isn’t
possible.
Scientists use indirect observations to gather clues about
Earth’s interior.
1. Seismic waves
Depending on the speed of the waves and the paths
they take, geologists uncover clues about the
inside of the Earth.
Waves can:speed up,
slow down,bend, or stop
2. Rock Clues
Since many rocks form far below Earth’s surface,
scientists can study what the rocks are made of and
make inferences about Earth’s interior.
Earth’s Layers
Scientists theorize that the earth is made up of
4 layers…
1. The Inner Core
It is solid, dense, and made of iron. There is great pressure in
the inner core.
5,000º C, hottest, most pressure
2. The Outer Core
It is made of molten (liquid)
metal.
3. The Mantle
It is the largest layer; it is solid, but flows slowly, like
putty.
4. The Crust
It is the thinnest layer, but its
thickness varies…
It is thinnest under the oceans. This is
oceanic crust.
It is thickest under the continents.
This is continental crust.
All features on Earth’s surface are part of the crust.
Pressure and temperature
increase as depth increases.
EARTH’S PLATES
The lithosphere is made up of the crust and the topmost part
of the mantle.
The lithosphere is broken into about
30 sections, or plates.
These plates “float” on the asthenosphere,
also part of Earth’s mantle.
Earth’s plates vary greatly in size and shape.
The plates move slowly, often taking more than a year to
creep a few centimeters.
Lasers and satellites are used to measure
these small plate movements.
The places where the edges of different
plates meet are called plate boundaries.
The constant movement of Earth’s plates creates
forces that affect Earth’s surface at those
boundaries.
PLATES THAT MOVE APART
Plates move apart because of tension (pulling forces).
When plates move apart, gaps form
between the plates.
The gaps are filled by magma that is pushed up and which cools to
form new crust.
The places where this new crust is formed are called mid-ocean
ridges.
PLATES THAT
COLLIDE
When plates collide, the
outcome depends on the density of
the plates.
Oceanic crust is more dense than continental crust.
If two continental plates collide, there is a pile up of crust;
this is called compression.
If two oceanic plates collide, or if an oceanic and a continental plate collide, the denser one
goes to the bottom.
This is called subduction.
PLATES THAT SLIDE
PAST
Shearing: When a force pushes
something in two different directions.
A transform boundary is a place where two
plates that are moving past one another meet.
Shearing at a transform boundary
causes faults and earthquakes to
occur.
WHY DO PLATES MOVE?
There are only theories about
why plates move.
The theory of convection currents is that movements are
caused by differences in density.
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