First 337 words of the document:
Fossils are the remains of organisms from many years ago, which are found in some
rocks. They provide evidence that organism lived ages ago. Fossils form in rocks in one
of three ways:
1) From GRADUAL REPLACEMENT BY MINERALS
. Things like teeth, shells and bones, which don't decay easily and can last a long
time when buried
. They're eventually replaced by minerals as they decay, forming a rock like
substance shaped like the original hard part.
. The surrounding sediments also turn to rock, but the fossil stays distinct inside
the rock and eventually someone digs it up
2) From CASTS AND IMPRESSIONS
. Sometimes fossils are formed when an organism is buried in a soft material like
clay. The clay hardens around it and the organism decays, leaving a cast of
. Things like footprints can be pressed into these materials when soft, leaving an
impression when it hardens
3) From PRESERVATION IN PLACES WHERE NO DECAY HAPPENS
. In amber (clear yellow stone made from fossilised resin) and tar pits there's no
oxygen or moisture so decay microbes can't survive.
. In glaciers it's too cold for the decay microbes to work
No one knows how life began
Fossils show how many of today's species have evolved over millions of years but we
don't know where the first living thing came from...
. There are many hypotheses suggesting how life first came into being, but no
one really knows.
. These hypotheses can't be supported or disproved because of the lack of
evidence that is reliable and valid.
. There's a lack of evidence because scientists believe many early organisms
were soft bodied and soft tissue tends to decay away completely. So the fossil
record is incomplete. Fossils that formed millions of years ago may have been
destroyed because of geological activity.