The modern challenge of climate change demands a sound scientific understanding of the Earth’s climatic history. Historic temperature and rainfall records are very important, but so is the geological evidence of climate recorded in sedimentary rocks that are formed on the surface of the Earth.
The late Neogene, a period of the Earth’s history beginning around 5 million years ago, was characterised by particularly dramatic climatic change around the globe. In Australia this was the time of change from a warm and wet climate, where lush rainforest covered much of southern Australia, to the arid climate we know today, where one-third of the continent receives rainfall of less than 250 mm per year.
However, despite considerable research, exactly when this change occurred and the reasons why it occurred remain poorly understood. Since the early 1980s geoscientists have thought that the big “drying out” occurred around 700–800,000 years ago, and that it was related to the build-up of ice in Antarctica and the associated changes in Southern Ocean circulation. Additional data collected since that time has added to our understanding but has not further refined the age or the origin of the change.
What we do know about climatic changes in the Neogene is revealed mainly from sediments preserved in deep sea environments. However, sediments on the continents...
