Palaeontology is a branch of earth sciences, which is essentially a study of plant and animal life in the past geological periods, millions of years ago. It deals with the successive plants and animals which have inhabited the earth since the earliest times, Evidence of their existence is left in the form of skeletons and bones buried in the rocks. These are known as fossils. Crucial evidence of human evolution is provided by the study of these fossils.
Sometimes, the buried body and the skeleton of an animal disintegrate entirely. If the surrounding material is sufficiently firm, a cavity may remain, having the exact outlines of the structures that disappeared. Such a cavity is called mold, Similar to molds are the impressions. These are left by extinct objects or parts of the body upon the surrounding material. The impression is made while the surrounding material is soft, like footprints in clay or lava. Footprints of extinct animals are also impressions affording valuable information about the animals that made them.
It is important to mention here, that early human fossils that have been found are generally fragmentary and incomplete. This is because only during the last 50,000 years or so, man started burying his dead. These later fossils are better preserved and, therefore, give us more information. For the earlier period, parts of bones are often the basis of imagining the re-construction of the whole skeleton. The finding of fossils deposits is both a matter of chance and of deliberate excavation in certain regions of the earth.