Richard Barclay opens an archive of the Smithsonian Natural History Museum that contains fossils nearly 100 million years ago. These rocks, despite their age, aren’t fragile. They are easy to handle by the botanist and geologist, who holds one in his hand for closer inspection.
A triangular, rounded leaf is embedded in the rock. The leaf was found on a tree at the same time as T-rex, triceratops and other prehistoric forest animals. However, it is immediately recognisable. Barclay said, “This is ginkgo. It’s a distinctive shape.” It hasn’t changed in millions of years.
Ginkgo trees are unique in that fossils of actual plant material are preserved, and not just a leaf’s impression. This thin layer of organic matter could be the key to understanding our planet’s ancient climate system and its possible future.
Barclay and his colleagues must first crack the code of the plant to access the information in the leaf.
Peter Crane, Yale University paleobotanist, said that “Ginkgo” is a very unique time capsule. 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.”
What can scientists learn from a fallen tree in an ancient forest?
Kevin Anchukaitis from the University of Arizona, said that scientists must look back at the past to see what’s ahead. “We want to know how the planet has reacted to climate change in the past, including how ecosystems have changed, ocean chemistry, sea levels, and how forests functioned.”
Scientists are particularly interested in “hothouse” periods where they believe that carbon levels and temperatures were much higher than they are 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.
Kim Cobb, a Georgia Institute of Technology climate scientist, said that scientists can also learn more about hothouse climates to improve their ability to project the future.
However, climate information from the distant past is not available. Scientists can study the carbon dioxide levels in ancient ice cores by studying air bubbles. However, these data only go back 800,000.
This is where the Smithsonian’s collection ginkgo leaves comes in. Barclay wanders down a maze of corridors to reach the 19th century when the Industrial Revolution began changing the climate.
He takes out sheets of paper from a cabinet and tapes ginkgo leaves that were taken from the botanical gardens at the time to tie them. Many specimens are labeled in beautiful cursive, one of which is dated Aug. 22, 1896.
The leaf shape is almost identical to that of a fossil about 100 million years ago and to one Barclay has in his hand. One key difference that can be seen under a microscope is how the leaf has reacted to carbon dioxide.
The tiny pores located on the leaf’s underside allow for carbon dioxide to be absorbed and water to be reabsorbed. This allows the plant to convert sunlight into energy. The plant requires fewer pores to absorb carbon when there is a lot of it in the air. The leaves will produce more pores when carbon levels fall.
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. He is able to see what the ginkgo leaves looked before humans significantly altered the atmosphere.
He now wants to find out what the pores in fossilized ginkgo leaf leaves can tell him about the atmosphere 100 millions years ago.
He needs a codebreaker and a translation sheet to decipher ancient atmosphere’s handwriting.
He’s conducting an experiment in a Maryland forest clearing.
Barclay and Ben Lloyd, the project assistant, tended rows of ginkgos in open-topped plastic sheets that allowed them to see sunlight, rain and change of seasons. Barclay stated, “We grow them in this way so that the plants experience natural cycles.”
Researchers adjust the amount of carbon dioxide that is pumped into each chamber. An electronic monitor outside displays the levels every five second.
Some trees are growing at the current levels of carbon dioxide. Some trees are growing at levels that are comparable to levels in the distant future or the past.
Barclay stated, “We’re searching for analogues — it is necessary to have something to compare with.” Researchers will be able to determine the atmosphere of the ancient past if there is a match between the specimen leaves and fossil leaves.
They are also studying the effects of super-charged environments on trees, and found that they grow faster when there is more carbon dioxide.
Barclay says that plants that grow quickly are more likely make mistakes and to be more vulnerable to damage. It’s similar to a race car driver who is more likely to get off the tracks at high speeds.
