Why study Earth's interior

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Why study Earth's interior?

• 8.1 How do geologists know about rocks in
  Earth's interior?
• 8.2 How do earthquakes help make images of
  Earth's interior?
• 8.3 How do we know ... how to determine
  velocities of seismic waves in rocks?
• 8.4 What composes the interior of Earth?
• 8.5 How hot is the interior of Earth?

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Why study Earth's interior?
Fig 8.1
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8.1 How do geologists know about rocks in Earth's
interior?
The size of Earth has been deduced as far back as
5 B.C. Earths mass is derived from our knowledge
of gravity. Using these we can calculate density.
Fig 8.5
Knowing the density of crustal rocks and
peridotite tell us that deeper material must be
much denser.
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How earthquake waves move through rock
Fig 8.7
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8.2 How do earthquakes help make images of
Earth's interior?
Shadow zones are areas where seismometers do not
record P or S waves (or both). The reason for
this is that P waves are refracted through core
mantle boundaries, and S waves are blocked by the
liquid outer core entirely.
Fig 8.15
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8.3 How do we know ... how to determine
velocities of seismic waves in rocks?
This graph shows the difference in P-wave
velocity in different geologic materials (and
water/air) at the same temperature/pressure
conditions.
Fig 8.17
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8.4 What composes the interior of Earth?
Table 8.1 summarizes the accepted physical
parameters of Earths layers. It takes into
account the data from many experiments, theories,
and field observations.
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8.4 What composes the interior of Earth?
A cross-section of Earth based on velocity
measurements based on seismic data. Density is
estimated from these data. Note that the core is
three times as dense as the mantle. The
crust-mantle boundary is named after its
discoverer,
Fig 8.19
Yugoslavian
seismologist Andrija Mohorovicicthe Moho, which
is 520 km below ocean crust and 2585 km beneath
continents.
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8.4 What composes the interior of Earth?

• Zones and boundaries of Earths mantle
• Low-velocity zone, a less-rigid zone thought to
  be near to its melting point. Marks the boundary
  between lithosphere and asthenosphere.
• Mantle transition zone, notes a change of mainly
  peridotite above and higher density minerals
  below.

The lower mantle is not well known and may be
part core, part mantle material. Certain aspects
will show up again in Chapters 10 and 12.
Fig 8.20
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8.5 How hot is the interior of Earth?
Fig 8.21 (top)
A geologic interpretation of Earths internal
temperature regime. The solid blue line is a
speculative gradient for the deeper Earth.
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8.5 How hot is the interior of Earth?
Fig 8.21 (bottom)
This continuation of the geothermal gradient down
into the deeper Earth to its core shows the
transitional zones. Much of the hypothetical
inner Earth gradient is derived from seismic data.