 The Australian Shield has a characteristic depth of 4.5 km and an estimated age of 2.8 to 3.5 billion years.In places younger sedimentary rock covers the shield's Precambrian surface.It occupies the portion of Australia west of a line running north–south roughly from the eastern shore of Arnhem Land on the Bay or Gulf of Carpentaria to the Eyre Peninsula in the state of South Australia, and skirting to the west of the Simpson Desert in the interior.