When Antarctica Was a Jungle: The Lost Continent Under the Ice

Okay so I need to tell you about the thing that broke my brain a little when I first read about it. Antarctica was once a jungle. An actual, dense, warm, swampy rainforest, teeming with plants and trees and life, sitting at the South Pole while dinosaurs were doing their thing everywhere else.

And the evidence for this is not speculative. Researchers drilled into the seabed near the Pine Island and Thwaites glaciers and pulled up a sediment core. Inside one section of that core, they found a dense network of fossil roots so well preserved they could see individual cell structures. They found pollen and spores. They found the first remnants of flowering plants ever discovered at that latitude.

This forest existed 90 million years ago. It was not at the edge of Antarctica. It was within 560 miles of the South Pole.

What Antarctica Was Actually Like

In the mid-Cretaceous period, around 90 to 115 million years ago, Earth was running hot. Sea surface temperatures in the tropics reached around 95 degrees Fahrenheit. Sea levels sat roughly 558 feet higher than they are today. CO2 in the atmosphere ran somewhere between 1,120 and 1,680 parts per million. For context, we are currently at around 420 parts per million and already watching ice sheets destabilize.

Antarctica at that time still sat at the South Pole. It had not drifted. It still experienced four months of complete polar darkness every year. And despite all of that, it was warm enough to sustain a dense, swampy temperate rainforest similar to what you find in New Zealand today. Average summer temperatures were around 66 degrees Fahrenheit. Rainfall was comparable to modern Wales.

The trees that grew there included conifers and tree ferns. Researchers have found fossil tree fragments in the Transantarctic Mountains dating back 260 million years, meaning forests were growing on Antarctica even before the dinosaurs existed. Before. The. Dinosaurs.

Why It Stopped Being a Jungle

Here is the part where the story gets complicated, because the honest answer is that we do not fully know.

The leading explanation involves the shifting of tectonic plates. As Antarctica separated from Australia and South America over tens of millions of years, the Drake Passage opened up between Antarctica and the tip of South America. That opening allowed the Antarctic Circumpolar Current to form, a powerful ocean current that effectively isolated Antarctica from warmer water flowing from the tropics. Surrounded by cold water and cut off from warm ocean circulation, temperatures on the continent dropped. Ice began to accumulate. The ice reflected sunlight rather than absorbing it, which cooled things further. The whole system locked itself into the frozen state we recognize today.

CO2 levels also dropped significantly over this period, removing the atmospheric insulation that had kept the planet warm enough to sustain equatorial-level temperatures near the poles.

The transition was not instant. It played out over millions of years. But at some point, the rainforest died, the continent froze over, and the ice buried everything underneath it.

What Is Still Down There

This is the part I think about most. The ice sheet covering Antarctica averages about 1.3 miles thick. In some places it reaches nearly 3 miles deep. Underneath all of that ice, there is a continent. It has mountains, valleys, lakes, and river systems. It has a landscape that has not seen sunlight in millions of years.

Researchers using radar have mapped parts of the land beneath the ice, and what they find keeps surprising them. There are lakes down there, liquid lakes kept from freezing by geothermal heat from below, that have been sealed from the atmosphere for potentially millions of years. Lake Vostok, the largest of these subglacial lakes, contains water that last touched air around 15 million years ago.

Scientists genuinely do not know what is living in those lakes. They suspect something is. Life finds a way in the most extreme conditions we have ever looked, and a sealed, liquid, geothermally warmed lake under two miles of ice seems like exactly the kind of hostile environment that bacteria would consider a reasonable home.