Usually after a living organism dies, its body rapidly decays or is consumed by predators, scavengers or bacteria. After a short period of time, no trace remains. However, in some cases the remains of an animal or plant are rapidly buried in sediment. This occurs through a natural process, such as mud being washed over a floodplain after a storm or by soil slipping down into an open cave. If the chemistry of the surrounding sediment is correct then the animal or plant may be preserved.
The word “fossil comes from the Greek ossilis – literally meaning “dug up". In science, fossils are objects that represent traces of animals or plants.
Over long periods of time (millions of years) the sediment hardens into solid rock.
Sometimes after an animal is buried, groundwater moves through the sediment deposits leaving behind additional minerals within the skeleton. These minerals may alter the colour and texture of a fossil, but often the overall shape and internal structure is preserved. Excellent examples of this process in the Richmond area are shark teeth and fish bones, which have been impregnated with carbon and are stained dark brown.
Sometimes the remains of the plant or animal continue to decay after burial, leaving a gap or hole within the ground. Groundwater passing through the sediment eventually deposits new minerals within the empty space, forming a perfect cast of the original object. Another excellent example of this process is Petrified Wood which is commonly found in the Richmond area.
If the chemistry of the fossil and the sediment are similar, then no change may take place. The fossil may continue to retain its original composition. Many of the fossils found around Richmond are preserved this way. The shell fossils are still made out of calcium carbonate minerals. The reptile bones are still made calcium phosphate minerals, much like our own skeleton.
