Pictures in stone
Tucked away in the earth’s rocks there are often “pictures” from the
past.
Many times, in ages past, animals walked through mud and left
footprints. Slowly, over thousands of years, the mud hardened into rock.
The footprints were preserved forever. We have found rocks in which
there are footprints of dinosaurs and other animals. We have even found
rocks with the footprints of prehistoric people.
Leaves of ancient plants and feathers from the first kinds of birds also
fell into the mud. They, too, left prints that were preserved when the
mud hardened into rock.
Ancient snails, clams, and other shelled sea creatures died and were
covered up with mud. The mud hardened around them. When their soft parts
rotted away, and their shells dissolved, a hole was left in the rock—a
hole the exact shape of the dead animal. This hole was like a mold.
Slowly, it filled up with minerals that hardened into stone. The stone
was the exact shape the dead animal had been.
These pictures and shapes in stone are called fossils. They tell us
about the plants and animals of millions of years ago.
