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A team working in an ice-free region of dry valleys in the western Olympus Range in Antarctica last summer discovered a rare trove of plants and animals high in the mountains, with perfectly preserved fossils of mosses, diatoms and minute crustacea called ostracods  -a rare snapshot of ancient life in what must have been the last traces of tundra on the interior of the southernmost continent before temperatures began to drop relentlessly, which saw it change from a climate like that of South Georgia to one similar to that seen today on Mars.

"We've documented the timing and the magnitude of a tremendous change in Antarctic climate," said Prof David Marchant, of Boston University last summer. "The fossil finds allow us to examine Antarctica as it existed just prior to climate cooling at 13.9 million years ago. It is a unique window into the past. To study these deposits is akin to strolling across the Dry Valleys 14.1 million years ago."

An abrupt and dramatic climate cooling of 8°C in 200,000 years forced the extinction of tundra plants and insects and brought interior Antarctica into a perpetual deep-freeze from which it has never emerged, though may do again as a result of climate change.

The international team combined evidence from glaciers, from the preserved ecology, volcanic ashes and modeling to reveal the full extent of the big freeze in a part of Antarctica called the Dry Valleys.

If we can understand how the Antarctic got into this relatively cold climate phase, then that can help predict how global warming might push us back out of this phase. For the vast majority of Earth history there was no permanent ice like is common today at the poles and even the tropics at high elevation. There's been a progressive cooling going on for 50 million years to get us into this permanent-ice mode; the formation of a permanent ice sheet on Antarctica plays a big role in that cooling.

Studies like this that establish when and how climate thresholds were crossed along the way can be used to predict climate thresholds going the opposite direction, from cool to warm.

The team was struck by how species of diatoms and mosses are indistinguishable from living ones. Today they occur throughout the world - except Antarctica.To think that modern counterparts have survived 14 million years on Earth without any significant changes in the details of their appearances is striking. It must mean that these organisms are so well-adapted to their habitats that in spite of repeated climate changes and isolation of populations for millions of years they have not become extinct but have survived.

What caused the big freeze is unknown though theories abound and include phenomena as different as the levels of carbon dioxide in the atmosphere and tectonic shifts that affected ocean circulation.

Posted by Jason McManus. Image: Mount Boreas in the western Olympus Range, Dry Valleys.

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