Dirty secret: Soil reveals Antarctica had rainforests 90M years ago

Scientists have discovered a dirty little secret about Antarctica: the frigid wasteland of a continent was once home to a swampy temperate rainforest when dinosaurs walked the Earth some 90 million years ago, according to an analysis of ancient soil samples.

Ferns, conifer trees and a wide variety of flowers once flourished near the South Pole during Earth’s super-warm Cretaceous Period, according to the study published Wednesday in the journal Nature. The discovery is expected to reshape scientists’ understanding of the planet’s climate history and — potentially — the future.

Summer temperatures soared as high as 25 C in Cretaceous Antarctica, while the annual average temperature was about the same as present-day Toronto or Montreal (12-13 C), the study shows.

“This warmth was only possible because there was no Antarctic ice sheet and because the atmospheric carbon dioxide concentration was significantly higher than indicated by climate models to date,” the researchers said in a news release.

You probably wouldn’t have wanted to hang around for the winter. Antarctica would go through four months of night each year, leaving the plants and animals with no sunlight for long stretches of time. Nevertheless, plants managed to flourish on the continent long before it became what it is today, researchers said.

“We now know that there could easily be four straight months without sunlight in the Cretaceous,” geoscientist and study co-author Torsten Bickert said in the news release. “But because the carbon dioxide concentration was so high, the climate around the South Pole was nevertheless temperate, without ice masses.”

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An international team of researchers managed to unlock all of these secrets by analyzing a large chunk of soil recovered from the ocean floor of the Amundsen Sea in February 2017, about 900 kilometres from the South Pole.

They dropped a drill rig about one kilometre below the surface of the water, then burrowed down 27 metres to retrieve the hefty chunk of dirt. The scientists said they were shocked to find that the soil sample was from an ancient rainforest, not an ancient seafloor.

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Further analysis revealed that the dark brownish-grey soil was full of secrets, including a tight network of fossilized roots, along with pollen and spores from 65 different plant species.

“If you would go to a forest near you and drill a hole, it would probably look pretty similar,” lead study author Johann Klages told Reuters.

The soil was composed of silt and clay, according to Klages, a geologist at the Alfred Wegener Institute in Germany.

“We had found a layer originally formed on land, not in the ocean,” he told CNN.

No dinosaur fossils were found in the sample, but Klages says there likely would have been various flying dinosaurs and insects living in the area at the time. Archeologists have found the odd dinosaur fossil in Antarctica in the past, mostly from that extremely warm Cretaceous Period.

The Earth looked very different during that time, when global temperatures were at their highest point in the last 140 million years. The continents were still closer together and in different configurations than they are now, and the overall sea level was much higher — about 170 metres above what it is today.

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Klages and his team were able to gather a vast amount of information from the soil sample, including evidence of the atmosphere and temperatures that the soil was exposed to when it was on the surface of the planet.

Klage says the discovery could help with future modelling around climate change, especially as humans continue to pump carbon dioxide into the atmosphere.

“We didn’t know that this Cretaceous greenhouse climate was that extreme,” he told The Guardian.

“It shows us what carbon dioxide is able to do.”

—With files from Reuters