Australia

Geologists determine the age of rock strata by examining the fossils they contain. Geologists and paleontologists examine strata and establish the age of their surrounding sediments based on the types of fossilized specimens they find. For example, tribolites, tiny animals with shells, flourished in the Cambrian period. So when geologists find sediments chock full of tribolite fossils they know they are dealing with Cambrian strata which they have determined to be 570 million to 500 million years old. Fossils are therefore geological signposts. Each geological period is characterized by specific types of fossilized organisms (plant and animal) the record for which has been formalized into the geologic time scale.

Such fossil testimony is spotty in eastern Australia except for a few areas including Broken Hill in western New South Wales, central Victoria and Tasmania. So while it is difficult to reconstruct an authoritative overall history of Australia in Cambrian times, some general conclusions can be withdrawn. One is that western Australia has a more stable geological history relatively speaking than the eastern section of the continent. There is much greater mobility and folding generally in the eastern half than in the west.