Ancient plants provide clues about life on Earth in warmer climates

Paleobotanist David Greenwood has been collecting fossil plants from Australia for many years, and some of them are so well-preserved that it’s hard to believe they’re millions of years old..

According to new research, Australia was now arid and once covered with lush forests. Image credit: Adobe Stock.

Such fossils contain information about the ancient world in which they flourished, and Greenwood and a research team including climatologist and researcher David Hutchinson of the University of New South Wales and UConn Department of Geosciences paleobotanics Tammo Reichgelt have begun the assembly process. put together evidence in an effort to learn more from the collection.

The results of the study were presented in Paleoceanography and paleoclimatology magazine.

Fossils date back 55 to 40 million years ago, during the Eocene. During that time, the world was much warmer and wetter, and these greenhouse conditions indicated that there were palm trees at the North and South Poles, and especially arid lands such as Australia were lush and green.

Reichgelt and co-authors sought evidence of variations in precipitation and plant productivity between the past and the present.

Because different plants tend to thrive under certain conditions, plant fossils have the potential to indicate the environment in which these plants lived.

By focusing on the morphology and taxonomic features of 12 different plants, the researchers came up with a more comprehensive view of the climate and productivity in the old greenhouse world of the Eocene era.

Reichgelt suggests that the morphological technique depends on the fact that the leaves of flowering plants – generally flowering plants – have a climate response process.

For example, if a plant has large leaves and is left in the sun and does not have enough water, it will start to shrink and die due to excessive evaporation.. Plants with large leaves also lose heat to their surroundings.

Tammo Reichgelt, Paleobotanist, Department of Geosciences, University of Connecticut

Reichgelt continued:Thus, finding a large fossil leaf means that the plant most likely did not grow in an environment that was too dry or too cold to cause excessive evaporation or appreciable heat loss.

These and other morphological features may be associated with an environment that we can quantify. We can compare fossils to modern plants around the world and find the closest analogyReichgelt added.

The second approach was taxonomic. “If you travel to the mountain, the taxonomic composition of the flora changes. Low on the mountain may be a deciduous forest dominated by maples and beeches, and as you go further into the mountain you will see more spruce and fir forest. “

Reichgelt stated: “Thus, finding beech and maple fossils probably means a warmer climate than finding spruce and fir fossils.. “

These climatic preferences of plant groups could be used to quantitatively restore the ancient climate in which plant group growth was found in the fossil community.

The findings suggest that the Eocene climate would be very different from today’s climate in Australia. The continent needed a steady supply of rainfall to maintain its lush green landscape. Warmer weather means more evaporation, which means that more rain was available in the Australian mainland.

Higher levels of carbon dioxide in the air at the time, 1500 to 2000 ppm, also contributed to the lush through a process known as carbon fertilization. Reichgelt describes that with a net amount of CO2the plants were essentially forgiving.

South Australia appears to have been largely forested, with primary productivity similar to seasonal forests, not unlike those here in present-day New England..

Tammo Reichgelt, Paleobotanist, Department of Geosciences, University of Connecticut

Reichgelt added:In the summer in the northern hemisphere, the carbon cycle is changing dramatically today, as large amounts of carbon dioxide are withdrawn due to primary productivity in a vast area of ​​forests that exist in a large belt around 40 to 60 degrees north. There is no such mainland in the southern hemisphere today in the same latitudes.

Reichgelt continued:But Australia occupied 40 degrees to 60 degrees south during the Eocene. As a result, there would be a highly productive large landmass in the southern hemisphere that would withdraw carbon, more than what Australia is doing today, because it is largely dry.. “

Hutchinson said geological evidence suggests that the climate is highly sensitive to CO2 and that this effect may be greater compared to what climate models predict.

The data also suggest that the polar warming was very strong and that our climate models also tend to underrepresent this effect. So if we can improve our models with a high CO content2 An eocene world, we could improve our predictions for the future.

Tammo Reichgelt, Paleobotanist, Department of Geosciences, University of Connecticut

Future projects will expand the data set to areas outside of Australia to ask what global productivity is doing during the global greenhouse climate.

We have large data sets of plant fossils that have been collected around the world, so we can use the same methods we use here to ask what will happen to global biosphere productivity.Reichgelt said.

With ever-increasing carbon emissions, there is an increasing study of what is happening in the biosphere with high water efficiency and high photosynthetic activity in plants.

Reichgelt describes that modern plants did not have time to evolve to change CO2 conditions. But a look back can help retrieve some of this data.

Reichgelt stated: “It will obviously take a long time for the plants to adapt to the changing CO2 levels, but the fossil flora gives us an insight into the biosphere of the ancient greenhouse worlds. “

Magazine link:

Reichgelt, T., et al. (2022) Plant Proxy Evidence for high precipitation and productivity in the Australian Eocene. Paleoceanography and paleoclimatology. doi.org/10.1029/2022PA004418.

Source: https://dpp.uconn.edu/

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