What are fossils?

Fossils are the traces of ancient animals and plants found buried in rock. Sometimes a fossil retains the shape and structure of the hard parts of an animal, such as fossilized dinosaur bones. These are not the original bones, because minerals have replaced them over millions of years, but they have the same shape. Other fossils are just the impression of an animal or plant, created when the plant or animal was buried in mud that has gradually solidified into rock. Even footprints of animals such as dinosaurs have been preserved. 

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How old are fossils?

Ancient history has been divided up into eras, which are periods of time identified by the fossilized forms of life from that period. The oldest era, called the Palaeozoic, contains fossils ranging from many primitive life forms up to some of the earliest land-dwelling animals. During this era, fishes, amphibians and early reptiles appeared. The Mesozoic era was the age of giant reptiles, when dinosaurs stalked the world. The Cenozoic era in which we still live is the age of mammals and birds. All fossils can be placed in these eras, which are subdivided further into smaller periods.

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