WHAT ARE FOSSILS?
The word fossil comes from the latin word “fossilis”, which means
“dug up”.
Most fossils are excavated from sedimentary rock layers.
Sedimentary rock is rock that formed from sediment, like sand, mud,
small pieces of rocks.
These small pieces are compressed under more and more layers of
sediment that piles up on top of it.
The layer that are farther down in the Earth are older than the top
layers.
HOW FOSSILS FORM?
Fossils of hard mineral parts (like bones and teeth) were formed in
this way:
some animals were quickly buried after their death in mud or in
sand
over time, more and more sediment covered the remains
the harder parts of the animal (bones and teeth) were encased in
the sediment
in the right circumstances, parts of the animals turned into fossils
over time
after a long time, the chemical in the buried animals' bodies
changes: water replaced the chemical in the bone with rock. The
process of fossilization involves the dissolving and the
replacement of the original minerals in the object with other
minerals.
The result is a fossil, a rock-like copy of the original object, in the
same shape, but chemically very different.
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HERE'S A FLOW CHART OF FOSSIL FORMATION:
THE SIX WAYS THAT ORGANISMS CAN TURN INTO
FOSSILS:
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unaltered preservation (like insects or plant parts trapped in
amber)
permineralization=petrification (rock-like minerals seep in slowly
and replace the original organic tissues with silica, calcite or pyrite,
forming a rock-like fossil; most bone and wood fossils are
permineralized)
replacement (an organism's hard parts dissolve and are replaced
by other minerals, like calcite, silica, pyrite, or iron)
carbonization=coalification (only the carbon remains in the
specimen - other elements, like hydrogen, oxygen, and nitrogen
are removed)
recrystalization (small crystals turn into larger crystals)
authigenic preservation (molds of organisms that have been
destroyed or dissolved).
Most animals did not fossilize; they simply decayed.
Paleontologists estimate that only a small percentage of the
dinosaur turned into fossils.
Most of the dinosaur skeletons that are shown in museums are not
actually fossils!
They are fiberglass or resin replicas of the original fossils.