Hardness of Mantle
Date: August 26, 2004
How hard is the earth's mantle?
Thanks for your question... it is a very good one. To be honest,
scientists do not yet know for sure how hard a mantle rock would be,
or even what it would be made of, but we do
have some pretty good ideas. You probably already know that the
mantle is very deep within Earth. If you wanted to make a hole deep
enough that would just reach the very top of the mantle, you would
need to use a very special kind of drill and make a hole at least 20
kilometers deep! And, to make matters worse, you would have to drill
the hole in the middle of the ocean! You could drill a hole on land,
too, but you would have to make an even deeper one (80 kilometers!) to
reach the mantle.
Drilling a hole to the mantle to collect rocks would be very difficult
and expensive, but luckily for geologists, there are other ways to
collect mantle rocks to find out what they are made of and feel like.
Sometimes when volcanoes erupt, they carry broken pieces of rock from
the mantle to the surface where they can be found by people. We know
that these rocks come from the mantle because they are very different
from the kinds of rocks that are normally made at Earth's surface.
They feel just as hard as other rocks when we pick them up off the
ground, but while they are still deep inside the mantle, they are a
little softer. The mantle is a very, very hot place, and hard rocks
can be made to feel softer when they are hot, just like M&M's become
softer when you hold them in your hand. But, even though the rocks in
the mantle are a little softer because of the high temperature there,
they are still very hard.
Scott J. Badham
Department of Geology and Geophysics
University of Wyoming
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