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The Layers of the Earth
© Copyright 2006. M. J. Krech. All rights reserved.
Earth’s Interior
• Geologists have used two types of evidence
to learn about Earth’s interior.
• Direct evidence: Rock samples
• Indirect evidence: Seismic waves
Rock Samples
• Geologists have drilled holes as deep as
12.3 Km into Earth.
• They obtained clues of structure and
conditions inside Earth.
• Laboratory rock samples are squeezed with
great force using laser beams.
Seismic Waves
• Geologist have recorded seismic waves and
study how they travel through Earth.
• Finding clues based in the speed and the
path seismic waves take. When the waves
reach specific depth the path change.
Layers of Earth
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Three layers: crust, mantle and core.
The layers vary greatly in:
Size
Composition
Temperature
Pressure
Pressure
• The deeper inside Earth, more pressure on
the mass of rocks.
• Pressure is a force pressing on an area.
Temperature
• Temperature inside Earth increases as depth
increases.
• Beneath earth surface rock is cool, but 20 meters
down the rock starts to get warmer.
• For every 40 meters down , the temperature
increases 1 Celsius degree.
• The high temperatures inside Earth are the results
of great rock pressure, energy released from
radioactive elements.
Age of Earth
• Earth was formed 4.6 billions years ago.
The Four Layers
The Earth is composed of four
different layers. The crust is
the layer that you live on.
The mantle is much hotter
and has the ability to flow.
The outer core and inner
core are even hotter with
pressures so great you would
be squeezed into a ball smaller
than a marble if you were able
to go to the center of the Earth!
The Crust
The Earth's Crust is like
the skin of an apple. It is
very thin in comparison to
the other three layers. The
crust is only about 5- 80
Km.
It is thickest under the
mountains ( continental
crust ) and thinnest
beneath the ocean.
(oceanic crust).
The Crust
• The oceanic crust is made of basalt ( fine,
dark rock)
• The Continental crust is made of granite (
coarse, light rock).
• Both rocks are Igneous.
The Crust
The crust is composed of two rocks. The continental
crust is mostly granite. The oceanic crust is basalt.
Basalt is much denser than the granite. Because of this
the less dense continents ride on the denser oceanic
plates.
The Lithospheric Plates
The crust of the Earth is broken into many pieces called
plates. The plates "float" on the soft, semi-rigid
asthenosphere.
The Mantle
• The mantle is made of hot rock , but solid,
Scientists divide the mantle into layers
based on the physical characteristics of
those layers.
• Overall the mantle is about 3,000 Km thick.
The Lithosphere
The crust and the upper layer of the mantle
together make up a zone of rigid strong, brittle
rock called the Lithosphere.
Earth’s lithosphere is nearly 100 Km. thick.
The Asthenosphere
The asthenosphere
is the semi-rigid
part of the middle
mantle that flows
like hot asphalt
under a heavy
weight and
pressure. This part
of the mantle can
bend as a metal
spoon.
Mesosphere
• In this layer the mantle is hot but more rigid
because of increasingly high pressure. This
layer has a TRANSITION ZONE and
includes the lower mantle which connects to
the core.
The Mantle
The Mantle is the
largest layer of the Earth.
The middle mantle is
composed of very hot
dense rock that flows like
asphalt under a heavy
weight. The movement of
the middle mantle
(asthenosphere) is the
reason that the crustal
plates of the Earth move.
Convection Currents
The middle mantle "flows"
because of convection
currents. Convection
currents are caused by the
very hot material at the
deepest part of the mantle
rising, then cooling and
sinking again --repeating
this cycle over and over.
Convection Currents
The next time you heat anything like
soup or water in a pan you can watch
the convection currents move in
the liquid. When the convection
currents flow in the asthenosphere
they also move the crust. The crust
gets a free ride with these currents,
like the cork in this illustration.
Safety Caution: Don’t get your face
too close to the boiling water!
The Core
• The core is made of metals iron and nickel.
It consists of two parts:
• A dense, liquid outer core.
• A dense solid inner core.
The Outer Core
The core of the Earth
is like a ball of very
hot metals. The
outer core
is so
hot that the metals in
it are all in the liquid
state. The outer core
is composed of
molten metals:
nickel and iron.
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
like a liquid, but are
forced to vibrate in
place like a solid.
The core also contains:
oxygen, sulfur and
silicon.
The Core and Earth’s Magnetic
Field
• Scientists believed that movement in the
liquid outer core creates Earth’s magnetic
field.
• The planet acts as a giant magnet.
• Using a compass, the compass needle aligns
with the lines of force in Earth’s magnetic
field.
The End
BONUS:
Answer this question:
Have we ever seen part
of the Mantle? Explain.
© Copyright 2006. M. J. Krech. All rights reserved.