The Earth’s Structure
A Journey to the Center of the Earth
The Interior of the Earth
The Earth’s Layers
 Earth can be divided
into three main layers –
the crust, mantle and
core.
 The layering is due to
differences in density
 Temperature and
pressure in Earth’s
interior increase with
depth
The Crust
 Rocky outer layer of
Earth
 Made up of Silicates
 Two types of Crust


Continental Crust –
rocks that make up
continents; thickness
between 8 -75 km
Oceanic Crust – rock
that makes up ocean
floor; average
thickness 7 km
The Mantle
 A thick layer of hot
semi-solid dense rock
 Approximately 2850
km thick
 Composed of mostly
iron, magnesium and
aluminum.
 Makes up about 84%
of Earth’s volume
“Sub Layers” in the Crust &
Mantle
Lithosphere – composed
of the oceanic and
continental crust and the
rigid upper mantle; thin
outer shell of Earth;
broken up into “plates”.
Asthenosphere – softer
and weaker rock in the
mid-mantle; can flow
slowly when under
pressure
Mesosphere – stronger
lower part of the mantle
The Core
 A large sphere of
metal that occupies
Earth’s center
 Composed mostly of
iron and nickel
 Divided into 2 parts:


Outer core – composed
of liquid metal; 2260
km thick
Inner core – solid due
to very high pressure;
1220 km thick
How do Scientists study Interior
of Earth?
 Use of Seismic Waves
 2 Types of Seismic Waves: S & P waves

P waves:



Travel through solids, liquids and gases
Faster than S waves
S waves

Travel only through solids
 Speed and direction of both waves are
affected by the composition of material
they are traveling through
Shadow Zones
 Locations on
Earth’s surfaces
where neither S or P
waves are detected
 S waves will not
travel through liquid
core
 P waves speed and
direction change
causing them to
bend