WASHINGTON (AP) – Richard Barclay opens a metal drawer in the archives of the Smithsonian Natural History Museum that contains nearly 100 million-year-old fossils. Despite their age, these rocks are not fragile. The geologist and botanist handles them with ease, placing one on his palm to examine it more closely.
Incorporated into the ancient rock is a triangular leaf with rounded upper lobes. This leaf fell from a tree around the time T-rex and triceratops roamed the prehistoric forests, but the plant is instantly recognizable. “You can say this is ginkgo, it’s a unique form,” Barclay said. “It hasn’t changed much in many millions of years.”
What is also special about ginkgo trees is that their fossils often preserve the actual plant material, not just the impression of a leaf. And this thin layer of organic matter may be key to understanding the ancient climate system and the possible future of our global warming.
But Barclay and his team must first break the plant code to read the information contained in the old leaf.
“Ginkgo is a pretty unique time capsule,” said Peter Crane, a paleobotanist at Yale University. As he wrote in “Ginkgo”, his book on the plant, “It’s hard to imagine that these trees, now elevated above cars and travelers, grew with the dinosaurs and have come down to us almost unchanged for 200 million years.”
If a tree fell in an ancient forest, what can you tell scientists today?
“The reason scientists look back at the past is to understand what will come in the future,” said Kevin Anchukaitis, a climate researcher at the University of Arizona. “We want to understand how the planet has responded in the past to large-scale climate change: how ecosystems changed, how ocean chemistry and sea level changed, how forests worked.”
The interest of scientists is of special interest in “greenhouse ”Periods in which carbon levels and temperatures cross they were significantly higher than today. One of these occasions occurred during the end of the Cretaceous (66 to 100 million years ago), the last era of the dinosaurs before a meteor crashed into Earth and most species became extinct.
Learning more about greenhouse climates also provides scientists with valuable data to test the accuracy of climate models to project the future, says Kim Cobb, a climate scientist at Georgia Tech University.
But climate information about the distant past is limited. Air bubbles trapped in ancient ice cores allow scientists to study ancient levels of carbon dioxide, but they only date back to about 800,000 years ago.
That’s where the Smithsonian’s collection of ginkgo leaves comes in. For a corridor of corridors, Barclay shines for millennia (as is only possible in a museum) until the 19th century, when the Industrial Revolution had begun to change the climate.
From a cabinet, he removes sheets of paper where Victorian-era scientists engraved and tied ginkgo leaves plucked from the botanical gardens of his time. Many copies have labels written in beautiful italics, including one dated August 22, 1896.
The shape of the leaf is virtually identical to the fossil from about 100 million years ago, and to a modern leaf that Barclay has in his hand. But a key difference can be seen with a microscope: how the blade has responded to the change in carbon in the air.
The tiny pores at the bottom of a leaf are arranged to absorb carbon dioxide and breathe water, allowing the plant to transform sunlight into energy. When there is a lot of carbon in the air, the plant needs fewer pores to absorb the carbon it needs. When carbon levels drop, the leaves produce more pores to compensate for them.
Today, scientists know the global average level of carbon dioxide in the atmosphere there are about 410 parts per million, and Barclay knows how the leaf looks like. Thanks to Victorian botanical leaves, he knows what ginkgo leaves looked like before humans had significantly transformed the planet’s atmosphere.
Now he wants to know what pores of fossilized ginkgo leaves can tell him about the atmosphere 100 million years ago.
But first you need a code breaker, a translation sheet, a kind of Rosetta stone to decipher the writing of the ancient atmosphere.
That’s why he’s doing an experiment on a forest clearing in Maryland.
One morning earlier this year, Barclay and project assistant Ben Lloyd tended rows of ginkgo trees inside open enclosures of plastic sheets that exposed them to rain, sunlight, and changing seasons. “We grow them this way so that the plants experience natural cycles,” Barclay said.
Researchers adjust the pumped carbon dioxide in each chamber and an outdoor electronic monitor flashes levels every five seconds.
Some trees grow at current levels of carbon dioxide. Others grow at significantly high levels, approaching levels of the distant past or perhaps the future.
“We’re looking for analogues, we need something to compare,” Barclay said. If there is a match between the appearance of the leaves in the experiment and the appearance of the fossil leaves, this will provide researchers with a rough guide to the ancient atmosphere.
They also study what happens when trees grow in overloaded environments and found that more carbon dioxide makes them grow faster.
But Barclay adds: “If plants grow very quickly, they are more likely to make mistakes and be more susceptible to damage. … It’s like a race car driver who’s more likely to get off the rails at high speed. “
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Follow Christina Larson on Twitter: @larsonchristina
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The Associated Press Health and Science Department is supported by the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.