** FOSSILS**
Hidden away among the rocks found in the earth crust are beautifully preserved remnants of organisms that lived thousands and millions of years ago.
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One of the most fascinating and important sciences that comprise geology as a whole is palaeontology , the study of fossils ...... WHAT ARE FOSSILS ?? ...... Fossils are the preserved remains of dead animals or plants that existed in bygone geological ages. In general, only the hard parts of organisms become fossilised , mainly bones,teeth,shells and wood. Sometimes, however, the entire organism can be preserved , this can happen when creatures become stuck in amber resin. This is called INCLUSION , when they are buried in peat bogs, in saline deposits, in natural pitch , or when they are frozen in ice.
Among the many exciting discoveries that have been made in bitterly cold Artic regions like northern Canada, and Siberia in Russia, are the perfectly preserved remains of woolly mammoth and rhinoceroses. But such finds are exceptional , when they do occur , they hit the headlines all over the world.
The 1st is called PERMINERALISATION . This takes place when liquids that contain silicon or calcite come from underground and replace the original organic components of the creature or plant that has died there . This process is known as REPLACEMENT or MINERALISATION. In many places throughout the world, silicfied sea urchins are often found in chalk deposits, and they are one of the main fossils to look out for on your own field trips.
If the fossilised organism contains soft tissue , flesh and muscle, for example , the hydrogen and oxygen that made up its structure in life are released, leaving behind only the carbon. This carbon firms a black film in the rock in the outline of the original organism . These outlines are called MOULDS , and the mounds over very thin organisms like leaves are known as IMPRINTS. When the tracks, footprints or fossilised faces , coprolites, of animals are pressedand preservedin this way they are called TRACE FOSSILS.
The best conditions for fossilisation occur where there his been rapid segmentation, especially in those parts of the seabed that lie deep enough to be undisturbed by water movement above them, generally speaking, each fossil will be the same age as the stratum of rock in which it lies, or at least it will be younger than the layer directly below it and older than the layer directly above .
Thus if scientists know the age of rock, they can calculate the age of the fossil. Perhaps the most momentous result of this came in the 19th century, when British scientists discovered the remains of mysterious creatures that they knew from the surrounding strata must have lived some 65 million years ago. These fearsome looking animals which had previously been completely unknown , were given the name Dinosaurs, from the Greek word meaning Terrible Lizards.
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