Written in stone - evidence of past climates


Victoria has a superb record of climate change, and in the geological past we have fantastic limestone cliffs like at Port Campbell, we’ve got coal seams, we’ve got a huge record of climate in the geological past. Now this climate was quite different to today; it was much warmer and wetter and the evidence for the warmer and wetter climate is preserved in the Latrobe Valley coal measures.

For example here we have a bit of Gippsland coal, and while this coal was being deposited rainfall was many times more than today. Temperatures were five or six degrees centigrade higher and it’s a swamp essentially, with lots of tree ferns and very, very lush forests that covered all of Victoria during this time.

The evidence also from marine conditions is very well preserved in all the limestones that we are blessed with in Victoria. For example here we have a bit of limestone which has a whole pile of microscopic fossils called forams, which are benthic — they lived on the seabed — and these are species that live today off Brisbane in waters that are four or five degrees higher than today around Victoria.

Fifteen million years ago, there was a pronounced cooling of the climate. And how do we know this? Well, the brown coal seams stopped being deposited and all the tropical animals in the sea migrated back to Brisbane and, to be replaced by much colder marine creatures and colder vegetation.

Eventually by seven million years, you had the Eucalyptus forests appear in Australia and that tells us that everything is starting to get dryer, there’s a bit more fire in the landscape, and by two to three million years ago we had basically almost today’s vegetation, where lots of eucalypts and no more rainforest species or very few rainforest species existing. And this is associated with expansion of ice in Antarctica.

Every time the ice sheet expanded in Antarctica, the rainforests died down, the tropical species from the sea migrated away and then when it melted, everything got warmer and wetter and this has happened many times in the geological past, especially in the last two million years. And the evidence is preserved fantastically in the rocks.

About this Video

Stephen Gallagher, University of Melbourne, explains what geology reveals about Victoria’s past climate.
Length: 02:44