The Layers of the
Earth!
Geologists study the process that create Earth features and
search for clues about Earth’s history.
Studying Surface Changes
Finding Indirect Evidence
• Forces above and below the
surface of the Earth are
constantly changing Earth’s
appearance.
• Geologists cannot observe
Earth’s interior directly.
Instead, they must rely on
indirect methods of
observation. Scientists record
seismic waves and how they
travel through the Earth in
order to make some inferences
about the Earth’s interior.
•
•
Constructive forces shape the
surface by building up mountains
and landmasses. Example: the
formation of the island of Surtsey
through volcanic eruptions.
Destructive forces slowly wear
away mountains and eventually
every other feature on the surface.
•
Example: Ocean waves that wear
away a coastline.
Journey to the Center of the
Earth
Temperature
• About 20 meters down, the
temperature of the surrounding
rock begins to get warmer. For
every 40 meters, that you
descend from that point, the
temperature rises 1◦C. This
rapid rise in temperature
continues for several
kilometers. After that, the
temperature increases more
slowly, but steadily.
Pressure
• The deeper you go, the
greater the pressure.
Pressure is the force
pushing on a surface or
area. Because of the
weight of the rock above,
pressure inside the Earth
increases as you go
deeper.
Earth Layers
• The Earth is divided into four main
layers.
*Inner Core
*Outer Core
*Mantle
*Crust
The Crust (between 5 – 40 km thick)
• The Earth’s crust is like
the skin of an apple. It
is very thin compared to
the other three layers.
•
The crust is thinnest beneath the ocean
floor and thickest under high mountains.
Oceanic crust consists of a rock , basalt.
Continental crust , forming the
continents, is mostly of a less dense rock ,
granite.
*The crust makes up 1% of the Earth.
Sometimes scientists say that the crust
has another layer called the lithosphere
which rests on the very bottom of the
crust and another one that rests on the
top portion of the mantle called the
asthenosphere.
*The crust of the Earth is
broken into many pieces
called plates.
Two sub-layers
Lithosphere
In Greek, “lithos” means
stone
This is a rigid layer located
at the very bottom of the
crust (where the plates are
found). It is about 100 kms.
Thick.
Asthenosphere
• In Greek, “asthenes”
means weak
• The asthenosphere
(located at the very top of
the mantle) is not weak
but soft. The material in
this layer can flow slowly,
allowing the plates to
move on top of it.
The Mantle
• The mantle is the
layer below the
crust.
• The mantle (molten
rock) is the largest
layer of the Earth,
about 3000 kms
thick.
• The mantle is
divided into two
regions: the upper
and lower sections.
Outer Core (2250 Km thick)
* The core of the
Earth is like a ball
of very hot metals.
* The outer core is
molten liquid (iron
and nickel).
* The outer core is
made up of iron and
nickel and is very
dense.
Inner Core (1200 kms thick)
* The inner core of
the Earth has
temperatures and
pressures so great
that the metals are
squeezed together
and are not able to
move.
* The inner core is a
solid.
Earth’s Magnetic Field
(Magnetosphere)
Currents in the liquid
outer core force the solid
inner core to spin at a
slightly faster rate than
the rest of the planet.
These currents create
the Earth’s magnetic
field, which causes the
planet to act like a giant
bar magnet. Like a
magnet, the Earth’s
magnetic field has a
North and a South pole.
Review
1) What are the four layers of the Earth?
2) The Earth’s crust is very ______?
3) The mantle is the largest layer of the
Earth? True or False
4) Is the Outer Core a liquid or a solid?
Answers!
1) Crust, Mantle, Outer Core, Inner Core
2) Thin
3) True
4) Liquid