Fossil leaves can reflect the climate in the last days of the dinosaurs.

WASHINGTON – Richard Barclay opened a metal drawer in the archives of the Smithsonian Natural History Museum that contained fossils that are about 100 million years old. Despite their age, these stones are not fragile. Geologists and botanists handle them easily, placing one in their palm and examining it closely.

Embedded in the ancient rock is a triangular leaf with round upper lobes. The leaf fell from the tree as T. rex and Triceratops roamed the prehistoric forests, but the plant is immediately recognizable. “You can tell it’s ginkgo, it’s a unique shape,” Barclay said. “It hasn’t changed much in millions of years.”

What is special about ginkgo trees is that their fossils often preserve the original material of the plant, not just the impression of leaves. And that thin sheet of organic matter could be the key to understanding the ancient climate system – and the possible future of our warming planet.

But Barclay and his team first need to break the plant’s code to read the information in the ancient address.

Peter Gran, a yellow botanist at Yale University, said: “Ginkgo is a very unique time capsule. As he wrote in his book Ginkgo on plants, Are over, have grown up with dinosaurs, and for almost 200 million years we have had almost no change. “

If a tree fell into an ancient forest, what can it tell scientists today?

“Scientists look back at the past because of what’s happening in the future,” said Kevin Encouchites, a climate researcher at the University of Arizona. “We want to understand how the planet has responded to large-scale climate change in the past – how the ecosystem has changed, how the sea chemistry and sea level have changed, how forests work.”

Of particular interest to scientists is the “hothouse” period when they realize that carbon levels and temperatures were significantly higher than they are today. One such event occurred at the end of the Cretaceous (66 million to 100 million years ago), the last time dinosaurs lived before a meteorite hit the Earth, and most species became extinct.

Learning more about hothouse climate provides valuable data for scientists to test the accuracy of climate models to predict the future, says Kim Kobe, a climate scientist at Georgia Tech University.

But climate information about the distant past is limited. Air bubbles trapped in ancient icebergs allow scientists to study ancient carbon dioxide levels, but they go back only 800,000 years.

This is where Smithsonian’s collection of ginkgo leaves comes in. Beneath a warp of corridors, Barclays stops for thousands of years – as is possible in just one museum – until the 19th century, when the Industrial Revolution began to change the climate.

From a cabinet, he retrieves sheets of paper where Victorian scientists tapped and tied ginkgo leaves from botanical gardens of their time. Many of the patterns have beautifully cursed labels, including the date August 22, 1896.

The shape of the leaf resembles fossils from about 100 million years ago, and a modern leaf Barclays is in his hand. But one important difference can be seen with a microscope – how the leaf responds to converting carbon into air.

Tiny holes are made in the underside of the leaf to allow carbon dioxide and respiration to enter the water, allowing the plant to convert sunlight into energy. When there is too much carbon in the air, the plant needs fewer holes to absorb the carbon it needs. When the carbon level falls, the leaves make more holes for compensation.

Today, scientists know that the global average level of carbon dioxide in the atmosphere is about 4 million parts per million – and Barclays knows what the shape of a leaf is. Thanks to Victorian botanical sheets, he knows what ginkgo leaves looked like before the human planet’s atmosphere changed dramatically.

Now he wants to know if the holes in the fossilized ginkgo leaves could tell him about the atmosphere 100 million years ago.

But first it needs a code breaker, a translation sheet.

That’s why he’s running a deforestation experiment in Maryland.

One morning earlier this year, Barclays and project assistant Ben Lloyd planted rows of ginkgo trees inside the open-top walls of a plastic sheet that exposed them to rain, sunlight and changing seasons. “We’re growing them so that plants can experience the natural cycle,” Barclay said.

Researchers adjust the pumped carbon dioxide in each chamber, and an electronic monitor outside shines the surface every five seconds.

Some trees are growing at the current level of carbon dioxide. Others are rising to significantly higher levels, estimating levels in the distant past, or perhaps the future.

“We’re looking for analogs – we need to compare something,” Barclay said. If experiments show how the leaves look and how fossil leaves match, it will provide researchers with some guidance for the ancient environment.

They are also studying what happens when trees grow in a more charged environment, and they find that more carbon dioxide increases them faster.

But Barclay added: “If plants grow too fast, they are more likely to make mistakes and more likely to be damaged. … It’s like a race car driver getting off a train at high speed. Is more likely. “

Follow Christina Larson on Twitter: sonlarsonchristina.

The Associated Press Health and Science Department is supported by the Department of Science Education at Howard Hughes Medical Institute. The AP is fully responsible for all content.

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