The Ground We Walk On
Margaret M. Loos
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BEDROCK
If we watch a film strip or movie showing the scientific view of how the earth was formed, we see a layer of basement rock which underlies the crust of the earth. Under the oceans it is formed of
basalt
and under the continents this bedrock is termed
granitic
. The granitic material has a lighter density than the basalt and, therefore, the continents rose above the waters. The bedrock is divided into plates composed of oceanic or continental bedrock which have been colliding since the beginning. Influenced by the layer under the plates, the
mantle,
the collisions have disturbed and reshaped those plates. Scientists are agreed that there are three major layers to the earth (based on seismic wave studies) the
core
, which extends from the center of the earth to about 1,800 miles below the surface, the
crust
, which extends between 18 to 25 miles beneath the surface, and the
mantle
, between the two.
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