Download Layers.of.Earth.part.2

Earth’s Layered Structure (part 2)
The Earth’s Interior
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We last discussed these points:
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How we know about the interior of the Earth…
How Earth’s interior took on its characteristics
The layers of the Earth as defined by
composition
 Today
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we will discuss:
The layers of the Earth as defined by
their behavior…
Layers Due to Behavior
 The
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Inner Core
Solid metal sphere at Earth’s center
 High
pressure maintains solidity
even though temperatures are
high enough to melt metal
 Only 1200 km thick
Layers Due to Behavior

The Outer Core
Liquid, metallic core
 High temperature creates convection
currents

Vertical motion in a fluid like boiling water
 Hot liquids are less dense (and so rise);
cool liquids are more dense (and so sink)
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Layers Due to Behavior
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Motion of the liquid metal produces a
magnetic field – Earth’s “magnetosphere”

Without the magnetic field, Earth would be
subjected to deadly radiation from the sun
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Therefore, without the outer core, there
would be NO LIFE on Earth
Layers Due to Behavior
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The magnetic field is due to the combined
properties of the outer core
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It is metallic AND it is liquid AND in motion
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ALL THREE are required to produced the
magnetic field
 For example – Mercury has an iron core, but no
magnetic field because it is solid!
 Venus has a liquid iron core, but it has no
magnetic field because there is very little motion
within the liquid
Moving outward - The
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Lower Mantle
The lower mantle is a thick layer of
mostly solid rock (over 2200 km thick)
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However, rock is not rigid – it can flow like
a thick liquid (like cold honey)
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Is responsible for heat transfer from the
core outward
Continuing upward - The Asthenosphere

The asthenosphere is part of the
UPPER MANTLE
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It is consider a “plastic” zone – not
completely molten, but not really rigid
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Rocks in the asthenosphere are very close
to their melting points and so deform easily

Convection in this region is thought to be
the driving force of plate tectonics
The Asthenosphere
Finally, The Lithosphere

The lithosphere consists of the uppermost
mantle and the entire crust

It is a solid, rigid layer that is broken into
several “plates”
 Lithospheric plates are large segments of the
lithosphere that consist of oceanic and/or
continental crust
 Seven major and many minor plates (has
changed throughout Earth’s history)

Plates are in constant motion
The Lithosphere
Motion in the Lithosphere

In the lower layers of the Earth (core,
mantle), motion is dominated by convection
(which is circular in motion)

At the surface, this motion translates into
lateral (sideways) motion of the plates
Motion in the Lithosphere

Two basic forces are thought
to control plate motion at the
surface of the Earth:
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Ridge-push

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As new crust is generated at a
mid-ocean ridge, the new crust
(assisted by gravity) pushes the
older crust aside
Slab-pull

When oceanic crust is forced
under continental crust, the
suction of the downward slab
pulls the rest of the plate toward
the trench
Motion in the Lithosphere

Both forces act in tandem (together) along with
convection to move the plates
Summary – Can you Answer?
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What are the five layers of the Earth as defined by
behavior?
Why is the inner core solid?
What is the importance of the outer core?
What is the major role of the lower mantle?
How is the asthenosphere different from the
lithosphere?
What is the importance of the asthenosphere?
What are lithospheric plates?
What are the two forces that control plate
motion?
What is the basic reason for plate motion?