The birth and death of a mountain range
Mountain ranges rise where a sea once met a shore. They start to form
when a sea bottom along the edge of a continent begins to fill up with
mud and sand. As the mud and sand grow thicker, the sea bottom begins to
sink. The mud, sand, and rock drop slowly down into the earth’s
mantle—the hot rock beneath the crust. They are crushed, squeezed, and
melted together by heat and pressure. Hot rock from the mantle is mixed
in with them. All this takes many millions of years.
Mountains are born when this mixture of rock is pushed up again by
earthquakes and other forces in the earth. As the huge pile of rock
rises, it pushes the edge of the land into wrinkles and folds. After
many more millions of years, the upper part of the long, lumpy mass of
rock has risen high above the land. Mountains now sit where once the sea
met the shore.
As soon as mountains are born, they begin to wear down. Rain falls on
them. Each drop, like a little bomb, breaks off tiny bits of rock. Wind
blows off tiny grains of rock and carries them away. Streams and rivers
run down the slopes, cutting great grooves. Sometimes, huge masses of
ice and snow move down mountainsides, grinding the rock to powder.
For millions of years, all these forces wear tons and tons and tons of
rock from mountains. Slowly, the proud, peaked mountaintops are worn
down and smoothed out. After many millions of years, nothing is left of
a mountain range but a row of small, smooth hills. After more years,
even those are worn away.
Mountains begin to form on a-sea bottom hundreds of millions of years
ago.
During millions of years, mud, sand, and hot rock are mixed together and
pushed up out of the sea bottom. This forms a long chain of wrinkled
mountains.
During many millions of years, wind, rain, and snow slowly wear down
mountains.
