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.