Slides in this set
From Gradual Replacement By minerals
Things like teeth, shells, bones, which don't decay
easily can last a long time after they've been buried.
They are eventually replaced by minerals as they
decay, this forms a rock like substance shaped like
the original part.
The surrounding sediments also turn to rock, but
the fossil stays distinct inside the rock.…read more
Casts and Impressions
Sometimes, fossils are formed when an organism is
buried in a soft material like clay.
This clay later hardens around it and the organism
decays, leaving a cast of itself. An animal's burrow or
a plants roots can be preserved as casts.
Things like footprints can be pressed into these
materials when soft, leaving an impressions when it
In amber (a 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
Peat bogs are too acidic for decay microbes.…read more
No one knows for sure
Fossils show how certain species have evolved over
millions of years although we do not know where
the first living organism came from.
The hypotheses suggesting different ways in which
it was made etc. can't be supported or disproved
because there's a lack of valid or reliable evidence.
This could be because fossils that did form may
have been destroyed by geological activity.…read more