Inside the Earth
Planet Earth
• All objects on or near Earth are
pulled toward Earth’s center by
gravity.
• Earth formed as gravity pulled small
particles together, that would collide, build
mass, and collect more particles.
• Early Earth generated thermal energy in its
interior, making the rocks of the planet soft
enough to flow.
Formation of Earth’s Layers
• Earth developed distinct layers of
different material according to their
densities (Do you remember
DENSITY?).
• When ancient Earth started melting,
the densest materials sank and
formed the innermost layer.
• The least dense materials stayed at
the surface and formed a separate
layer, and materials with intermediate
densities formed layers in between.
Temperature and pressure increase as
depth increases inside Earth.
Composition (What it is made of)
• Core
• Mantle
• Crust
Core
-Outer core – liquid
iron & nickel
-Inner core – solid
iron & nickel
The Inner Core
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.
The Outer Core
The outer core is
liquid.
• The outer core is
made up of iron and
is very dense.
• Because the outer
core contains iron,
when it flows it
generates a magnetic
field. This is the
source of the Earth's
magnetic field.
Mantle
-Much thicker layer – about 2,900 km
-Contains most of Earth’s mass.
-Molten rock
-Magma comes from mantle
The Mantle
• The mantle is the
largest layer of the
Earth.
• The mantle is
divided into two
regions: the upper
and lower sections.
• The upper mantle is
a solid while the
lower mantle is
more fluid.
Mantle cont.
• The layer of rocks within
the mantle, where the
rock is soft enough to
flow, is called the
asthenosphere.
Convection Currents
As the molten material in the asthenosphere is heated by the core it
becomes less dense and rises.
The material cools because it gets further away from the heat
source. Because it’s cooler, it’s more dense so it sinks.
It’s now closer to the heat so it all begins again!
The Crust
• Outer layer
• 5-100 km thick
• Makes up only 1% of
Earth’s mass.
• 2 types of crust
– Oceanic (very dense,
made of basalt)
– Continental (less
dense, made of
granite)
Oceanic and Continental Crust
The crust is typically about 25 miles thick beneath continents, and
about 6.5 miles thick beneath oceans. The crust is relatively light
and brittle. Most earthquakes occur within the crust.
Physical Structure of the Earth
(5 Layers)
• Lithosphere- rigid outer
layer crust +upper mantle
• Asthenosphere- solid rock
that flows slowly (like hot
asphalt)
• Mesosphere- middle layer
• Outer Core- liquid layer
• Inner Core- solid due to
pressure, very dense
Tectonic Plates
• Earth’s lithosphere is broken into about 19
pieces
• These plates move on top of the
asthenosphere due to convection currents.