Plant fossils reveal details about ancient flora and climate when the world was warmer than today
Posted May 2, 2008
Just 500 kilometers from the South Pole, on a warm day, you might seek shelter from the sun in a temperate forest, one that would appear somewhat familiar yet perhaps a little strange, with oddities like long-trunked trees sporting fern-like leaves.
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You would just have to go back in time by about 200 to 250 million years for such a pleasant, surreal stroll.
It’s in this deep geologic timeframe that Edith L. Taylor, a paleobotanist at the University of Kansas, seeks answers to how flowering seed plants, the dominate flora species today, evolved over time. She recently received a three-year grant from the National Science Foundation (NSF) to continue laboratory work on Antarctic plant fossils collected earlier this decade from the Beardmore Glacier area.
“This is going to be critical to modeling plant evolution and the development of seed plants,” said Tom Wagner, program director for Antarctic Earth Sciences at NSF’s Office of Polar Programs.
Taylor, along with her co-principal investigator Tom Taylor, has literally collected thousands of kilograms of plant parts in rocks in Antarctica. The collection from the Permian to Early Jurassic periods is from a time when scientists hypothesize that flowering plants began to evolve.
“They appeared rather abruptly and quickly took over the world,” Edith Taylor said. “Who was their ancestor? Nobody has been able to answer that question.”
Taylor and her lab team may find some clues to that question in the well-preserved specimens at the University of Kansas, which boasts one of the largest collections of Antarctic plant fossils in the world.
“The beauty of these plants is that they’re petrified, and all of the cells and tissues inside them are intact. You have a lot more characteristics that can allow you to say, ‘Oh, yeah, I think this leaf is something that could evolve into that leaf, because I can see the anatomy,’” she explained.
The name of this rare preservation process is permineralization. Permineralized deposits can reveal a great deal of information about a plant’s anatomy, morphology and reproductive biology.
“The plants in [the rocks] are not replaced by minerals, so they’re still organic,” Taylor said. “What makes these special is that these are petrified peat deposits. It would be like turning a compost heap in your backyard to stone, basically.”
The little pieces of plant stems, leaves and cones likely fell into a surrounding or nearby body of water, probably a swampy area, which contained a lot of silica from local volcanic sands. The silica eventually solidified, entombing the plant.
“[Permineralization] had to [happen] pretty darn fast, because in the Antarctic material we find embryos, stages in the development of embryos that don’t last very long,” she said.
“The first thing a paleobotanist does is to put all the parts back together essentially,” Taylor added. “You need to have a range of specimens to do that so you know you’re looking at different plants instead of just variations in a single plant.”
One of the main groups of plants the scientists study is glossopterids, an extinct group of seed plants that arose during the Permian. They became a dominant part of the flora that once flourished on Antarctica when it was part of the great southern continent of Gondwana. The group accounts for about 80 percent of the plant fossils the Taylors have recovered from the Permian.
The glossopterids were present for the entire Permian, a stretch of some 40 million years, according to Taylor. “That’s a lot of time for one plant group to dominate the landscape,” she noted.
They’ve also discovered tree trunks with rings, indicating flora with a seasonal lifecycle, as well as Triassic ferns that reproduced by seeds versus modern ferns, which propagate through spores.
The specimens the Taylors collected are also important in reconstructing the paleoclimate during a time when the world was warmer and when levels of carbon dioxide (CO2), a key greenhouse gas, were presumably higher than today.
“If we really want to know what the organisms would look like in the future, the only place we can go is the deep fossil record, because only in the fossil record do we find organisms living within five degrees of the pole in Antarctica where nothing lives today,” Edith Taylor explained. “The time period we live in now is an unusual one because the poles are cold, and most of geological time the poles have been warmer.”
The lab work involves sawing the rocks with diamond blades, etching them in hydrofluoric acid, and then squirting acetone, the main ingredient in nail polish and paint thinner, on the surface. A piece of plastic is then rolled over the specimen, allowed to dry, and then pulled away, to reveal a thin section of the plant in the rock.
“You can grind it and peel it, and grind it and peel it, and go right through the thing looking at the plants,” Taylor said. “We’ve basically been able to reconstruct [a] whole plant. … It’s really unusual in paleobotany to be able to reconstruct an entire plant.”
And though she may be looking at something many millions of years old and extinct, Taylor may be getting a glimpse of the not-so-distant future.
“We’ve reached a point where the only way we’re really going to understand how organisms are going to live as the world gets warmer is to look at deep time,” she said.
NSF-funded research in this story: Edith L. Taylor, University of Kansas.