The 280 million-year-old forest in the South Pole

(CNN)Antarctica as we know it is a frosty wilderness covered in thick compacted ice.

But a recent scientific discovery suggests that the vast white continent was home to leafy forests, some 280 million years ago.
During the last Antarctic summer, geologist Erik Gulbranson and a team of polar scientists chanced upon fossils from the oldest polar forest found on the continent -- before the first dinosaurs walked the Earth.
    Now the team is braving the land of ice once more to uncover clues as to how forests once flourished there.
    Erik Gulbranson on site in Antarctica.
    Antarctica was much warmer 280 million years ago than it is today. Back then, it was still part of Gondwana, the Southern Hemisphere supercontinent that incorporated present-day Africa, South America, Arabia, India and Australia.
    According to Gulbranson the southernmost part of the continent would have been carpeted in seed ferns extending up to 40 meters tall.
    These trees would have been able to survive approximately four to five months of absolute darkness, followed by four to five months of continuous light.
    However, their rings reveal a high frequency of very bad years of growth, says Gulbranson, suggesting it wasn't an easy environment for these trees to live in.
    Fossil trees are somewhat inconspicuous and therefore difficult to find.

    Finding trees in Antarctica

    Fossil hunting in Antarctica involves combing parts of the Transantarctic Mountains that extend across the continent, dividing it into East and West Antarctica.
    But traversing glaciers and snowfields is no easy feat in negative temperatures and fierce winds upwards of 40 miles per hour. Roped together with climbing harnesses and kitted out with steel spikes on their hiking boots, Gulbranson and his team probe for cracks in the ice to avoid falling down deadly crevasses.
    "It's very apparent from day one that as a human being you're not supposed to be there," Gulbranson tells CNN. "You might as well be on the moon or the bottom of the ocean."
    Once the team reaches the very top of the mountains the hunt begins, scouring for clues among the rocks.
    "Finding [tree] fossils is particularly challenging because they are somewhat inconspicuous, they blend into the rocks that they're found in," says Gulbranson.
    Gulbranson, who is a professor at the University of Wisconsin-Milwaukee, has been hunting Antarctic fossils for seven years, with a team of specialist scientists and mountaineers. They discovered fossils of 13 trees and various leaf fossil sites in the Antarctic Summer on a trip funded by the National Science Foundation between November 2016 and January 2017.
    "It was a really wonderful find that was completely unexpected," says Gulbranson.
    The fossils took five months to be ferried by boat and arrive at various laboratories around the world. Certain specialists are tasked with jigsawing parts of plants together, while others study leaf fossils, woody stems or tree rings.
    Gulbranson studies tree rings for clues about how these trees grew in polar ecosystems.

    The clue in volcanic ash

    One of the big challenges is dating the fossils. Gulbranson explains that 280 million years is just a rough estimate, and the polar forest could be 20 million years older or younger.
    The rough age of the fossil forest was determined by dating the leaf fossils found nearby and the plant pollen preserved in the sedimentary rock.
    The plan this time is to extract a mineral called zircon from volcanic ash for more accurate radiometric dating.
    "The forest we found last year was buried by volcanic ash, and that's probably why it preserved so well," explains Gulbranson.
    This form of uranium lead dating will give a much closer numerical age, within about a 10,000 year uncertainty.
    The team is also hoping to compare these polar forests with "younger" tree fossils.
    "One of our main goals of our research is to study how these polar ecosystems changed during what was the most significant mass extinction in the history of life," he says.
    The mass extinction at the end of the Permian period 250 million years ago was so severe it wiped over 90% of all species off the face of the earth, including Gulbranson's polar forest.
    While it is not known exactly what caused the mass extinction, one theory attributes it to a massive injection of carbon dioxide into the atmosphere over a timespan of 200,000 years, explains Gulbranson. The result was higher global temperatures and ocean acidification, he says.

    Arctic forests of the future?

    In studying tree rings on fossils from before and after the extinction, Gulbranson surmises that only one species of tree existed in this carbon dioxide rich ecosystem prior to the extinction.
    After the extinction, he says there was less carbon dioxide in the atmosphere, a higher diversity of evergreen and deciduous trees and a much more stable ecosystem.
    Gulbranson says his work could help us understand the effects of contemporary climate change.
    He says modern-day global warming may lead to forests migrating towards to the North Pole, in places like Arctic Siberia and Arctic Canada.
    "We know there's some connection between the gas concentration in our atmosphere and the types of ecological health that we might expect to see on our planet," he says.