Sometimes
we find the remains of plants and animals which lived millions of years ago and
have since turned to stone. These remains are called fossils. When the animal
died, long, long ago, by drowning, for instance, its body sank to the bottom of
the water and gradually layers of sand or silt were deposited over it. Over a
period of thousands of years, the silt turned to stone and so did the remains
of the animal which were preserved in it. In this way the fossils of many
animals and plants were formed. These fossils can tell us a great deal about
life on earth many millions of years ago. There are even some fossils that we
burn in our homes to keep warm. These are, of course, in the form of coal.
Millions of years ago, whole forests sank down, were covered and slowly
petrified. These ancient-tree-trunks are now coal. Among the coal that is found
in coal-mines, there are often numerous animal fossils as well.
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