Fossils are a faithful recording of 54 , an accurate imprint of the past. 55 ,
imagine a prehistoric fish swimming around in the sea a few million years ago. One day,
the fish dies 56 its body sinks down to the water bottom, where it becomes buried in
soft mud.
57 time passes, the flesh decays and 58 . An imprint of the skeleton stays
in the mud, even after the skeleton itself disintegrates. Many years pass. The mud with
59 gradually hardens and turns to stone under the pressure of the rock layers that
have subsequently built up on 60 .