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Earth’s Layers
Page 30 in your INB
Layers of the Earth

We discovered Earth
had layers of
different densities
through seismic
wave testing.

The three major
layers are the crust,
the mantle, and the
core.
The Crust

The top layer of the Earth is
called the crust.

There are two different
types of crust.

Oceanic Crust is the denser
layer, composed of basalt. It
is 7km thick on average.

Continental Crust is the less
dense layer, composed of
granite. It is 40km thick on
average.
The Mantle

The middle layer of the Earth is
called the mantle.

The mantle is both solid and
mobile.

It makes up 70% of the
Earth’s volume.

It is 2866 km thick on
average.

Material here flows very
slowly in responses to
changes in temperature
(affect density)
The Core

The innermost layer is the core.
The core can also be divided
into two parts.

The inner core is the center
of the planet.

The inner core is 1222 km
thick.

It is solid due to the intense
pressure and made of iron
and nickel.

Temperature ranges here
from 4000-5500 Celsius
The Core

The outer core is liquid

It is 2258 km thick on average.

It is a liquid shell that surrounds
the inner core.
The Lithosphere and Asthenosphere

In addition to the 3 layers, the
Earth can be divided up into
three other sections

The Lithosphere:

The strong, rigid surface
shell

Comprises the plates in plate
tectonics

Formed from the fusion of
the crust and the upper
mantle

Thinner in ocean basins

Thicker in continental
plates.
The Lithosphere and Asthenosphere

The Asthenosphere:

The weak, deformable region
in the mantle

The lithosphere rides on top
of the asthenosphere

Asthenosphere is partially
molten and moves the plates
above it.
Continental Drift

Alfred Wegener’s theory that a
supercontinent (Pangaea) was
broken apart by rotation of
Earth and tidal forces

Supported by South American and
African continents fitting together
on a map

First arose in the 1920’s

Huge controversy

Wegener couldn’t identify how the
continents moved apart.
Plate Tectonics and Sea Floor Spreading

In the 1950s, scientists began
using WWII technology to study
the ocean floor.

They discovered mid-ocean
ridges and trenches – areas of
spreading and receding as if the
ocean floor was an accordion.

In the 1960’s Princeton professor
H.H. Hess came up with the
concept of convection cells –
moving mantle patterns that
pushed magma up for form
ocean ridges.
Plate Tectonics and Sea Floor Spreading

Hess proposed that ridges
contained new rock and
seafloor.

He proposed that the edges of
the ocean basins where trenches
formed contained old dense
rock.

These old dense pieces
descended back down into the
mantle through subduction
Sea Floor Spreading


At ridges, new rock is being
pushed to the surface

In these areas the seafloor is
spreading out, making the ocean
basin bigger

The mid-Atlantic ridge is currently
making the Atlantic Ocean bigger.
At trenches and subduction
zones, the old rock is sliding
down into the mantle.