THE FOSSILS ARE THE REMAINS of plants and animals that have been preserved in rock. A fossil may be the preserved remains of an organism itself, an impression of it in rock , or preserved traces (known as trace fossils) left by an organism while it was alive, such as organic carbon outlines, fossilized footprints or droppings. Most dead organisms soon rot away or are eaten by scavengers. For fossilization to occur, rapid burial by sediment is necessary. The organism decays, but the harder parts-bones,teeth and shells foe example-may be preserved and hardened by minerals from the surrounding sediment. Fossilization may also occur even when the hard parts of an organism are dissolved away to leave am impression called a mould. The mould is filled by minerals, there by creating a cast of the organism. The study of fossils (palaeontology) can not only show how living things have evolved, but can also help to reveal the Earth,s geological history-for example , by aiding in the dating of rock strata.
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