Ancient pollen offers clues to how plants have adapted to climate change in the past – and potentially in the future | Smithsonian Voices

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56 million years ago, massive amounts of carbon entered the atmosphere and triggered a period of rapid warming. Fossilized evidence of how plants responded to these changes is preserved in places like Wyoming’s Bighorn Basin badlands.
Vera Korasidis, University of Melbourne

Every spring, many of us become hyper aware of pollen. The dust-like substance, which plants release en masse when they reproduce, is little more than a nuisance to many people as it irritates eyes and noses and coats cars in a green powder. light.

But for a palynologist, or pollen researcher, like the University of Melbourne‘s Vera Korasidis, the preserved pollen record “represents a truly unique record of the earth’s climatic history”. In his research, Korasidis uses fossilized pollen grains to reconstruct ancient ecosystems and climate.

Pollen is a particularly good time capsule for the environment. Plants have been producing pollen for hundreds of millions of years, investing large amounts of energy in dispersing reproductive material far and wide. Despite their small size, pollen grains are extremely durable. As a result, fossilized pollen is more common in many prehistoric deposits than relatively fragile fossil leaves.

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Despite their small size, pollen grains are durable, impermeable, and widespread, characteristics that increase their chances of preservation in the fossil record.

Vera Korasidis, University of Melbourne

As a postdoctoral researcher at National Museum of Natural HistoryKorasidis teamed up with Wing Scottthe museum’s curator of paleobotany, to examine 56-million-year-old pollen grains from one of the most dynamic periods in Earth’s climatic history, the Paleocene-Eocene Thermal Maximum (PETM).

Triggered by the release of massive stores of carbon dioxide into the oceans and atmosphere from bubbling volcanoes or massive methane leaks, the PETM was a time of rapid climate change. Geologists estimate that temperatures rose between 9 and 14 degrees Fahrenheit in less than 10,000 years and remained high for 150,000 years.

This rapid warming has completely transformed marine ecosystems. However, the impact of PETM on land is more difficult to analyze. Outside of a treasure trove of fossils from the multicolored badlands of northwest Wyoming’s Bighorn Basin, where Wing spent decades digging up leaf fossils, intact plant fossils from the era are hard to come by, making limits the overall understanding of how plants have responded to warming. temperatures.

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Wing and his team collected thousands of fossilized leaves from Wyoming’s Bighorn Basin, one of the few places where intact PETM leaves have been found.

Smithsonian Institution

To get a more comprehensive view, Korasidis, Wing and their colleagues analyzed resistant pollen grains preserved in rocks from 38 PETM sites around the world. “We’d like to have more of a movie than just a snapshot of what the changes have been like, and pollen gives us a better chance of doing that because it’s more easily preserved,” says Wing, co-author of the new to research. “It’s more likely to give you multiple images of what’s going on.”

In a new study published last month in the journal Paleooceanography and paleoclimatology, the team analyzed the fossilized pollen. Like snowflakes, different types of pollen have different shapes ranging from spiny spores to smooth grains. By matching grain shapes to modern plant pollen, researchers were able to cultivate a botanical who’s who from 56 million years ago, which in turn provided clues to what ancient environments were like during the PETM.

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Using a robust scanning electron microscope, Vera Korasidis was able to study the shapes and characteristics of a variety of fossilized pollen, including pollen from a palm tree (left) and a walnut tree (to right), with microscopic details.

Vera Korasidis, University of Melbourne

“We can make the connection between what we find fossilized and what exists today,” says Korasidis. “And that’s really the key – you have to be able to make that connection between the past and the present to infer past climates.”

Along with climate models, fossilized pollen revealed that warming temperatures during the PETM triggered an era of mass plant migrations. By dispersing their seeds, plants can move 500 meters or more per year, allowing plants to cover vast distances for thousands of years. During the PETM, many were trying to beat the heat by migrating to cooler climates at the poles and at higher altitudes.

According to Wing, these widespread movements created a mosaic of different types of plants mingling in the same environment. Wyoming was home to seasonally dry subtropical forests where plants common today in Central America thrived. In forests further north, temperate species such as birches have encountered tropical palms.

Although this botanical mixture seems odd today, it makes more sense when you consider that the PETM temperature spike occurred in an already warm world. There were no ice caps at the poles. Higher latitudes were humid and warm, while lower altitudes became hotter and drier. “It’s strange to think of palm trees growing in the Arctic, but it was such a different world,” says Korasidis. “It’s a world that doesn’t seem out of place to us today.”

These ancient plants weren’t the only ones feeling the heat during the PETM. Recent research has discovered that many early mammals, including the first dog-sized horses, reduced to beat the heat. With the increase in temperature, several archaic groups of mammals became extinct while other groups, including primitive primatesflourishes.

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Many early horses, including this Eocene Eohippus, were only slightly larger than the average dog. During the warmer temperatures of the PETM, the size of some of these “dawn horses” decreased by 30%.

Smithsonian Institution

While these examples from the PETM offer insight into how life may respond to a warmer future, Wing and Korasidis point out that modern climate change far exceeds even this prehistoric temperature peak. Researchers estimate that the rate of carbon dioxide entering the atmosphere today is 10 to 20 times faster than it was during the PETM.

This accelerated pace threatens to exceed the speed at which some plants can migrate.

During the PETM, some plants were able to move 15 degrees north in 10,000 years to keep pace with warming temperatures. However, even fast-moving plants can struggle to keep up with modern temperature changes.

Humans have also limited the movements of plants. Paved areas like cities and highways cut off the migration routes of some species. “Plants need a place for their seeds to disperse,” says Korasidis. While people have made it harder for plants to migrate, they can also help them migrate by opening up natural corridors of connected habitats and planting seeds of at-risk plants in more hospitable climates.

While PETM isn’t a perfect analog of modern climate change, Wing thinks it illustrates several important lessons, including how quickly excess carbon dioxide can warm Earth’s climate. Importantly, it also shows that once carbon enters the Earth’s atmosphere, it stays there.

“Even though the PETM is geologically short, it lasts 150,000 years, which is almost as long as there has been Homo sapiens on the planet,” says Wing. “So the next 150,000 years are going to be really different unless we figure out how to fix it before we end up adding a very large amount of carbon to the atmosphere.”

Related stories:
What Plant Fossils Reveal About Climate Change
Here’s how scientists reconstruct Earth’s past climates
Why Plants Seed Climate Studies
A drop in greenhouse gases caused global cooling 34 million years ago, study finds

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