Earth’s Internal Structure
What’s down below us?
Earth’s Internal Structure
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The Earth is made up of a variety of materials.
However, it is arranged into layers. The solid
materials of the Earth are separated into layers
according to composition and mechanical
properties.
Earth’s Internal Structure
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Earth can be divided into 3 main
compositional layers: (made up of different
materials)
Crust (outside of Earth)
Mantle
Core (very inside)
Earth’s Internal Structure
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Layers based on physical (mechanical)
properties are:
Lithosphere (most outer layer)
Asthenosphere
Mesosphere
Outer Core
Inner Core
Earth’s Internal Structure
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The Earth’s interior consists of a series of
shells of different compositions and
mechanical properties. Earth is called a
differentiated planet because of its
separation into layers. The Earth consists of
internal layers of increasing density toward
the center of the Earth.
Earth’s Internal Structure
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The internal layers were produced as different
materials rose and sank so that the least dense
materials were at the surface and the most
dense materials were in the center of the
planet. Therefore, gravity is the force behind
Earth’s differentiated planet.
Chemical Composition
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Crust is the outermost compositional layer of the
Earth.
Crust of the continents is distinctly different from the
crust beneath the ocean floor.
Continental crust is much thicker (up to 75km), is
composed of less-dense grantic rock, is strongly
deformed and includes the planet’s oldest rocks
(billions of years in age).
Oceanic crust is only about 8km thick, is composed
of denser volcanic rock called basalt and is
comparatively undeformed by folding and is
geologically young (less than 200 million years in
age).
Chemical Composition
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The mantle is the next major compositional layer of
the Earth. It surrounds or covers the core. The zone
is about 2900km thick and constitutes the great bulk
of Earth (82% of its volume and 68% of its mass).
The mantle is composed of silicate rocks that also
contain abundant iron and magnesium. Fragments of
the mantle have been brought to the surface by
volcanic eruptions. The mantle’s density increases
with depth (being the densest where it is closest to
the core).
Physical Properties
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Physical properties of a material are also
known as mechanical properties. They tell us
how a certain material responds to force, how
weak or strong it is and whether it is a liquid
or solid.
Physical Properties
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The lithosphere (rock sphere) is the solid,
strong and rigid outer layer of the Earth. It
includes the crust and upper most part of the
mantle. It varies greatly in thickness, from as
little as 10km in some oceanic areas to as
much as 300km in some continental areas.
Physical Properties
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The asthenosphere (weak sphere) is within the
upper mantle. In the asthenosphere the temperature
and pressure are just right so that part of the material
melts or nearly melts. Under these conditions, rocks
lose much of their strength and become soft and
plastic and flow slowly. Convection currents exist
here as the rock heats, becomes less dense, rises,
then cools near the lithosphere and drops back into
the depths of the mantle.
Physical Properties
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The mesosphere (middle sphere) is the region
between the asthenosphere and the core. The
rock here is stronger and more rigid than in
the Asthenosphere. This is because the high
pressure at this depth offsets the effect of high
temperature.
Physical Properties
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The Earth’s core has 2 distict parts:
The Inner Core:
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Is solid
Radius of about 1200 km
Chiefly made of iron
The Outer Core
 Is liquid
 Thickness of about 2270km (about twice of that of inner
core)
Physical Properties
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Earth’s core is extremely hot. Heat loss from
the core and the rotation of Earth cause the
liquid outer core to flow and rotate faster than
the inner core. This circulation generates
Earth’s magnetic flow.
Earth’s Outermost Layers
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The outermost layers of the Earth are the
atmosphere, hydrosphere and biosphere.
The atmosphere is composed of 78% nitrogen, 21%
oxygen and minor amounts of other gases such as
carbon dioxide and water vapour. The earliest
atmosphere was much different; it was essentially
oxygen free and consisted largely of carbon dioxide
and water vapour. The present carbon dioxide “poor”
atmosphere developed as soon as limestone began to
form in the oceans, tying up the carbon. Oxygen was
added to the atmosphere when plants evolved.
Earth’s Outermost Layers
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The hydrosphere is the total mass of water on the
surface of our planet. Water covers about 71% of the
surface. About 98% of this water is in oceans, while
only 2% is in streams, lakes, groundwater and
glaciers. It has been estimated that if the Earth’s
surface was smoothed out, a global ocean would
cover Earth to a depth of 2.25km.
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The biosphere is the part of Earth where life exists.