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The Asthenosphere
(a:without; stheno:strength; sphere:layer)
What is the asthenosphere?
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The asthenosphere is the layer of the
Earth just below the lithosphere that has a
texture comparable to warm tar.
The tectonic plates of the lithosphere float
above the asthenosphere.
It is composed of molten rock, or magma,
that is weak and can easily be deformed.
Where is the asthenosphere located?
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The asthenosphere is located directly
below the tectonic plates of the
lithosphere.
The asthenosphere takes up about 6% of
the mantle, but it is still capable of holding
up the tectonic plates.
The asthenosphere starts about 100 km
into the Earth, and is about 400 – 700 km
thick.
What happens in the asthenosphere?
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The temperature of 1,400 degrees to
3,000 degrees Celsius and pressure
conditions cause the asthenosphere to
have a texture similar to weak plastic.
The currents in the asthenosphere are like
convection currents; they flow outward
from the Earth’s interior.
Due to heat and pressure, igneous rocks
can form inside the asthenosphere.
How do other parts of the Earth interact
with the asthenosphere?
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In the asthenosphere, the rocks flow
because of the stresses of the churning
motion from the Earth’s deep interior.
The seismic waves coming from the
Earth’s deep interior slow down as they
pass through the asthenosphere. This is
how we know that the asthenosphere has
a ductile, or not brittle, manner.
The Discovery of the
Asthenosphere
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The asthenosphere was discovered by
geologists in the 1960s.
It was discovered because seismic waves
slow down as they pass though the
asthenosphere.