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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.