What is a fossil?
Fossils are preserved organisms or prints found in rock layers.
How are fossils formed?
Phase 1 - Death
Having died, the ammonite slowly sinks to the sea floor. Scavengers feed on the fleshy body of the creature, and after only several weeks all that remains is the shell.
Phase 2 - Deposition
Several months after death the shell gradually becomes covered with silt and sand. These layers continue to build, providing a shield around the shell and protecting it from damage. Time continues to pass and more and more layers are deposited. After a few hundred years the shell is several feet beneath the surface.
Time continues to pass, 1,000 years, 10,000 years and more...
Phase 3 - Permineralization
Gradually the chemicals in the shell undergo a series of changes. As the shell slowly decays, water infused with minerals passes through it, replacing the chemicals in the shell with rock-like minerals (Calcite, Iron or Silica). This process is scientifically known as 'permineralization'.
Over millions of years the original shell is completely replaced by the minerals and what remains is a rock-like copy of the original shell. The fossil has the same shape as the original object, but is actually rock. This process also results in loss of original colour.
Phase 4 - Erosion
Over millions of years the movement of the earth plates results in the seabed being forced above the surface. The result is a new landscape, within which the ammonite fossil remains buried.
Once above the surface the rock is subject to erosion. In certain areas of the world such as Lyme Regis in Dorset, the rock is once again subject to the affects of the sea. In these areas the rock is pounded by the sea, forming towering cliffs. Other factors such as wind, rain, ice and the sun help contribute to the rate of erosion.
Phase 5 - Exposure
Having laid beneath the surface for 150 millions years the fossil is finally exposed. This final stage may have resulted from a cliff collapse or the efforts of a paleontologist.
The fossil can then be removed from the ground, cleaned and examined.
Click here to see an animated fossil forming!! http://earthsci.terc.edu/content/visualizations/es2901/es2901page01.cfm?chapter_no=visualization
Where are fossils found?
in layers of sedimentary rock.
What are the different types of fossils?
Click here to watch animations on how molds and mineral replacement occurs!! http://www.panzainteractive.com/projects/fossils/