How Are Fossils Formed

How Are Fossils Formed

How are fossils formed? For fossil formation to take place a series of fortunate
events must occur. If any part of the series is missing, we will never see the
fossil! In fact, fossilization is a rare occurrence. Nature tends toward
recycling. That includes just about everything from plants and animals to rocks
and minerals.

Let?s narrow it down to just animals for a minute.
Animals, dead or alive, are food for other animals. From insects to dinosaurs,
an animal could be someone?s lunch! Any part of the animal?s body that isn?t
consumed is usually scattered about; leftovers! Just like those leftovers in
your fridge, these leftovers make great food for bacteria. In addition, these
leftovers are exposed to the elements: sun, rain, and even the soil itself all
help to breakdown and decompose the sturdiest of bones, shells and wood.


If we are ever going to see a fossil, some very specialized events must
intervene to ward off the natural process of decomposition. The following is the
most common scenario for fossil formation:

How Are Fossils Formed? Death
Is The First Step
To start with, an animal or plant must die in water or
near enough to fall in shortly after death. The water insulates the remains from
many of the elements that contribute to decomposition. An example may be
helpful. Let?s say that a trilobite has died of old age on the bottom of the
sea. Bacteria consume the soft body parts but leave the hard exoskeleton intact.


How are fossils formed? Step two is Sedimentation
As time passes,
sediments bury the exoskeleton. The faster this happens the more likely
fossilization will occur. Land and mudslides definitely help. River deltas are
also good for quick accumulation of sediments. This further insulates our
trilobite from decomposition.

The sediments themselves have a huge
influence on how well our trilobite fossil turns out. Very fine-grained
particles, like clays, allow more detail in the future fossil. Course sediments,
like sand, allow less detail to show. The chemical make up of the sediments also
contributes to the future fossil. If iron is present, it may give the rock a
reddish color. Phosphates may darken the rock to gray or black. The
possibilities are truly endless.

Permineralization
As the sediments
continue to pile on, the lower layers become compacted by the weight of the
layers on top. Over time, this pressure turns the sediments into rock. If
mineral-rich water percolates down through the sediments, the fossilization
process has an even better chance of preserving our ancient animal. Some of the
minerals stick to the particles of sediment, effectively gluing them together
into a solid mass. These minerals make an impact on our original trilobite as
well. Over the course of millions of years, they dissolve away the outer shell,
sometimes replacing the molecules of exoskeleton with molecules of calcite or
other minerals. In time, the entire shell is replaced leaving rock in the exact
shape of the trilobite.

Uplift
As the continental plates move around
the earth, crashing into each other, mountains are formed. Former sea floors are
lifted up and become dry land. This is exactly what has happened to our
trilobite. Now a fully formed fossil, our trilobite is buried under hundreds or
even thousands of feet of rock! Thanks to the movement of the plates, our
trilobite will come closer to the surface and nearer to discovery by some
fortunate fossil hunter. Luckily, nothing stays the same.

Erosion at
work
Rain, wind, earthquakes, freeze and thaw all work toward erosion. The
mountains that were built up are worn away over time. Our fossil trilobite once
again sees the light of day! With a little wisdom about where to look and some
luck, you may be the first one to find him!

This is the fossilization
process known as Permineralization. It is not the only answer to the question:
"How Are Fossils Formed?" There are many other ways that fossils can be formed.
You can read about them using the links below.

Source: http://www.ArticlePros.com/author.php?Claudia
Mann