Journey to the
Center of the Earth!

The Layers of the Earth
• When the Earth first formed gravity
pulled most of the heavy materials to
the center of the Earth
• Lighter materials “floated” to the
surface of the Earth
• As a result of gravity, the Earth
separated into four main layers

The Crust
• The thinnest layer of the Earth
–On average it is:
• 3 miles thick under the oceans
• 19 miles thick under the continents

The Crust
• There are two main types of crust:
– Continental Crust
• Thicker than oceanic crust
– Up to 35 miles thick
• Least dense layer in the Earth
– Oceanic Crust
• Much thinner than continental crust
• Slightly more dense than continental crust

The Crust
Nobody has ever drilled
through the crust

Crust

The Mantle
• Made up of heavier materials than the
crust.
• Slightly liquid
– Similar to silly putty or play-dough
• The largest layer in the Earth

The Mantle
• Asthenosphere
– A layer of the mantle just beneath the
crust.
• The asthenosphere is more fluid
than the rest of the mantle.

The Mantle
• Mohorovičić Discontinuity
– Also known as: the border between the
mantle and the crust.
– Called the “Moho” for short
– Named after Andrija Mohorovičić
who located the border.
http://www.earthscrust.org/earthscrus
t/science/historic/img/mohorovicic.gif

Mantle Moho
THICK LIQUID

Outer Core
• Located 1,800 miles beneath the surface
• Mainly made out of liquid iron and nickel
– The liquid iron moving around in the outer
core creates the Earth’s magnetic field.

Outer
Core
LIQUID
(Iron & Nickel)

Inner Core
• Located 3,200 miles beneath the surface
• Made from solid iron and nickel
• Very, very hot, but stays solid because the
entire Earth is pushing down on the inner
core.

Inner Core
SOLID
(Iron & Nickel)

Crust
Mantle Moho
Outer
Core
Inner
Core

How Do We Know?
• No one has even drilled through the crust,
so how do we know what the layers are?
– Earthquakes cause waves to go through the
center of the Earth
– Scientists use earthquake waves like a
submarine uses SoNAR.
• The waves bounce off the layers and tell scientists
where a boundary is located

Heat in the Earth
• The temperature in the center of the Earth
gets up to about 10,000°F
• Where does that heat come
from?

Where Does the Earth’s
Heat Come From?
1. Heat from when the Earth formed
Comets & Meteors striking the Earth
2. Radioactive Elements in the Earth
They decay and release huge amounts of heat.
3. Gravity pulling elements towards the center
of the Earth
Friction between materials rubbing against each other.