Even when Australia was close to the South Pole, the climate was relatively warm and wet, and this persisted for a long time despite changes in latitude. It was probably under this climate that the deep weathered, iron-rich profiles that characterise much of Australia were formed. Today a large part of Australia is arid or semi-arid. The dunes are mostly fixed now. Stony deserts or gibber plains are areas without a sand cover and occupy a larger area than the dune fields.
Salt lakes occur in many low positions, in places following lines of ancient drainage.
They are often associated with lunettes, dunes formed on the downwind side of lakes. Many important finds of Aboriginal prehistory have been made in lunettes. Despite the prevalence of arid conditions today, real aridity seems to be geologically young, with no dunes or salt lakes older than a million years. The broad shape of Australia has been influenced over long periods by earth movements associated with large tectonic processes. However, much of the detail has been carved by river erosion.