Some 90 million years ago, a temperate rainforest grew near the South Pole. Scientists recovered fossil traces of the ancient rainforest from seafloor sediment cores collected near West Antarctica's Pine Island Glacier.

Seismic data suggested the sediment layer was unique, but researchers weren't expecting to find the remnants of a Cretaceous forest.

"The finding of this well preserved 'forest soil' layer was actually a lucky dip," researcher Ulrich Salzmann, professor of palaeoecology at the University of Northumbria in Britain, told UPI. "We did not know of the existence of this layer before."

Among the sediment layers, Salzmann and his research partners found roots, pollen, spores and the remains of flowering plants. Scientists were able to use the various plant remains to piece together a fuller picture of what exactly Antarctica's ancient forest looked like.

"This was a swampy forest, dominated by needle-leaved conifer trees with many ferns. The forest was a temperate -- not a tropical -- rainforest, similar to the forests found today in New Zealand," Salzmann said. "Summer temperatures averaged 19 degrees Celsius and water temperatures in rivers and swamps reached up to 20 degrees. This was despite a four-month polar night, meaning for a third of every year there was no life-giving sunlight at all."

Scientists estimate the polar rainforest persisted until the Oligocene epoch, before fragmenting some 20 million years ago. Pockets of rainforest likely remained viable until 10 million years ago.

Antarctica and the South Pole has moved a bit over the last 90 million years, but tectonic shifts don't account for the emergence and disappearance of the ancient Antarctic forest. The polar forest was made possible by climate change.

The mid-Cretaceous period was one of the warmest periods in Earth's history. The atmosphere was flooded with CO2 and sea levels were more than 500 feet higher than they are today. Sea surface temperatures in the tropics were as high as 95 degrees Fahrenheit.

Researchers hope the latest findings -- published Wednesday in the journal Nature -- will help climate scientists perfect the models designed to predict the effects of today's human-caused climate change.

"These extreme warm worlds with high atmospheric carbon dioxide concentrations give us important insights into the mechanism and controls of climate in a future warmer world," Salzmann said. "By combining our paleo data with climate modelling in this particular study, we learned about the enormous potency of the greenhouse gas carbon dioxide, and how essential the cooling effects of today's ice sheets are."

Scientists are currently studying additional Antarctic sediment cores to better understand the evolution of the polar ecosystem over the last 60 million years.

"We are particularly interested in learning more about what forced the transition of the Antarctic continent from the warm Greenhouse environment to the cold ice house with permanent ice sheet we see today," Salzmann said.

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