Oroville Mercury-Register

Fossil leaves may reveal climate in last era of dinosaurs

- By Christina Larson

WASHINGTON >> Richard Barclay opens a metal drawer in archives of the Smithsonia­n Natural History Museum containing fossils that are nearly 100 million years old. Despite their age, these rocks aren’t fragile. The geologist and botanist handles them with casual ease, placing one in his palm for closer examinatio­n.

Embedded in the ancient rock is a triangular leaf with rounded upper lobes. This leaf fell off a tree around the time that T-rex and triceratop­s roamed prehistori­c forests, but the plant is instantly recognizab­le. “You can tell this is ginkgo, it’s a unique shape,” said Barclay. “It hasn’t changed much in many millions of years.”

What’s also special about ginkgo trees is that their fossils often preserve actual plant material, not simply a leaf’s impression. And that thin sheet of organic matter may be key to understand­ing the ancient climate system — and the possible future of our warming planet.

But Barclay and his team first need to crack the plant’s code to read informatio­n contained in the ancient leaf.

“Ginkgo is a pretty unique time capsule,” said Peter Crane, a Yale University paleobotan­ist. As he wrote in “Ginkgo,” his book on the plant, “It is hard to imagine that these trees, now towering above

cars and commuters, grew up 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 it tell scientists today?

“The reason scientists look back in the past is to understand what’s coming 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 changes in climate — how ecosystems changed, how ocean chemistry

and sea levels changed, how forests worked.”

Of particular interest to scientists are “hothouse “periods when they believe carbon levels and temperatur­es were significan­tly higher than today. One such time occurred during the late Cretaceous period (66 million to 100 million years ago), the last era of the dinosaurs before a meteor slammed into Earth and most species went extinct.

Learning more about hothouse climates also gives scientists valuable data to test the accuracy of climate models for projecting

the future, says Kim Cobb, a climate scientist at Georgia Institute of Technology.

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

That’s where the Smithsonia­n’s collection of ginkgo leaves come in. Down a warren of corridors, Barclay hops across millennia — as is only possible in a museum — to the 19th century, when the Industrial Revolution

had started changing the climate.

From a cabinet, he withdraws sheets of paper where Victorian-era scientists taped and tied ginkgo leaves plucked from botanical gardens of their time. Many specimens have labels written in beautiful cursive, including one dated Aug. 22, 1896.

The leaf shape is virtually identical to the fossil from around 100 million years ago, and to a modern leaf Barclay holds in his hand. But one key difference can be viewed with a microscope — how the leaf has responded to changing carbon in the air.

Tiny pores on a leaf’s underside are arranged to take in carbon dioxide and respire water, allowing the

plant to transform sunlight into energy. When there’s 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.

Today, scientists know the global average level of carbon dioxide in the atmosphere is about 410 parts per million — and Barclay knows what that makes the leaf look like. Thanks to the Victorian botanical sheets, he knows what ginkgo leaves looked like before humans had significan­tly transforme­d the planet’s atmosphere.

Now he wants to know what pores in the fossilized ginkgo leaves can tell him about the atmosphere 100 million years ago.

 ?? PHOTOS BY CAROLYN KASTER — THE ASSOCIATED PRESS ?? A distinctiv­e fan-shaped ginkgo leaf in the Fossils Atmosphere­s Project is seen in the morning sun at the Smithsonia­n Research Center in Edgewater, Md., Tuesday. “Ginkgo is a pretty unique time capsule,” said Peter Crane, a Yale University paleobotan­ist. “It is hard to imagine that these trees, now towering above cars and commuters, grew up with the dinosaurs and have come down to us almost unchanged for 200million years.”
PHOTOS BY CAROLYN KASTER — THE ASSOCIATED PRESS A distinctiv­e fan-shaped ginkgo leaf in the Fossils Atmosphere­s Project is seen in the morning sun at the Smithsonia­n Research Center in Edgewater, Md., Tuesday. “Ginkgo is a pretty unique time capsule,” said Peter Crane, a Yale University paleobotan­ist. “It is hard to imagine that these trees, now towering above cars and commuters, grew up with the dinosaurs and have come down to us almost unchanged for 200million years.”
 ??  ?? A Late Cretaceous ginkgo leaf fossils from Alaska’s North Slope is seen at the National Museum of Natural History in Washington, Friday. What’s special about ginkgo trees is that their fossils often preserve actual plant material, not simply a leaf’s impression. And that thin sheet of organic matter may be key to understand­ing the ancient climate system — and the possible future of our warming planet.
A Late Cretaceous ginkgo leaf fossils from Alaska’s North Slope is seen at the National Museum of Natural History in Washington, Friday. What’s special about ginkgo trees is that their fossils often preserve actual plant material, not simply a leaf’s impression. And that thin sheet of organic matter may be key to understand­ing the ancient climate system — and the possible future of our warming planet.

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