australian outback
Arid today, Australia was once covered by lush forests, according to new research. Credit: Unsplash/CC0 Public Domain

It is hard to believe that some of the fossil plants from Australia are millions of years old. The fossils hold details about the ancient world in which they thrived, and a team of researchers including climate modeler and research David Hutchinson, from the University of New South Wales, and the University of Connecticut have begun the process of reconstructing them. Their findings are published in a journal.

55 to 40 million years ago, the fossils were found. At that time, the world was much warmer and wetter, and this meant that there were palms at the North and South Pole, and Australia was lush and green. Reichgelt and co-authors looked for evidence of differences in precipitation and plant productivity.

Fossils of plants show what environments those plants lived in.

The researchers looked at the climate and productivity of 12 different floras by focusing on their features.

The leaves of flowering plants have a strategy for responding to climate, which is why Reichgelt explains the method.

Plants with large leaves lose water because they are left out in the sun. It is most likely that this plant was not growing in an environment that was too dry or too cold for excess heat loss to occur. The environment that we can quantify can be linked to these and other features. We can compare fossils to modern floras around the world.

If you travel up a mountain, the flora's classification can change. Reichgelt says that there may be a forest that is dominated by maples and beeches on the mountain.

The results show that the climate of the past would have been different to the present day. A steady supply of precipitation is required to sustain a lush green landscape. More rain was available to move into Australia's continental interior. The lushness was caused by higher levels of carbon dioxide in the atmosphere, 1500 to 2000 parts per million. Reichgelt says that plants were stuffing their faces because of the abundance of CO 2

Reichgelt says that Southern Australia seems to have been largely forested, with primary productivity similar to seasonal forests. There is no such landmass in the Southern Hemisphere today. Australia had a temperature of 40 degrees to 60 degrees south. During the Southern Hemisphere summer, there would be a highly productive large landmass, drawing down carbon more than what Australia is doing today since it is largely arid.

Hutchinson says the geological evidence suggests the climate is sensitive to CO 2 and that this effect may be larger than what our climate models predict. If we can improve our models of the high-CO 2 world, we might improve our predictions of the future.

Future projects will ask what global productivity does during a hothouse climate on a global scale.

Reichgelt says that they have large datasets of plant fossils that have been collected around the world, so they can apply the same methods that they use here.

With increasing carbon emissions there is more research going into studying what happens in the biosphere with increased photosynthetic activity and water use efficiency in plants. Modern plants have not had time to adapt to changing CO 2 conditions. By looking at the past, we can get some information.

It will take a long time for plants to adapt to changing CO 2 levels, but fossil floras allow us to peek into the biosphere of ancient hothouse worlds.

More information: Tammo Reichgelt et al, Plant Proxy Evidence for High Rainfall and Productivity in the Eocene of Australia, Paleoceanography and Paleoclimatology (2022). DOI: 10.1029/2022PA004418 Citation: Fossil plants reveal lush Southern Hemisphere forests in ancient hothouse climate (2022, May 31) retrieved 31 May 2022 from This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.