Antarctica, which is almost 4 times the size of the United States, is nearly completely covered by a miles-thick layer of ice.

The South Pole hasn’t constantly been frozen. When was the last time Antarctica was ice-free?

This ice cap formed fairly just recently in geological terms, professionals informed Live Science. “I believe the majority of people would state 34 million years back was when the ice sheet very first formed in Antarctica,” stated Eric Wolffa paleoclimatologist at the University of Cambridge.”[Previously] the majority of it would have resembled northern Canada today– tundra and coniferous forest.”

Worldwide temperature levels are an essential element affecting the level of ice protection. Around 50 million years back, the world had to do with 25 degrees Fahrenheit (14 degrees Celsius) warmer than it is today, however temperature levels progressively reduced over the following 16 million years. By 34 million years back– a period referred to as the Eocene-Oligocene limit– the environment was 14.4 F (8 C) warmer than it is today.

What activated this temperature level drop, and was that all it took for the ice sheets to form?

Related: Which is cooler: The North or South Pole?

“There are 2 aspects, and most likely both remained in play,” Wolff informed Live Science. “One of them is a modification in the co2 concentration of the environment, and the other is the motions of the continents and, in specific, the opening of the Drake Passage,” the strait in between South America and Antarctica that links the South Atlantic with the South Pacific.

The more co2 that’s in the environment, the more heat is caught and the warmer the world is.

From about 60 million to 50 million years earlier, the co2 concentration in Earth’s environment was truly high– someplace around 1,000 to 2,000 parts per million, or in between 2.5 to 5 times today’s levelsstated Tina van de Flierdta geochemist at Imperial College London.

“But we understand that the CO2 in the environment boiled down throughout that Eocene-Oligocene border,” she informed Live Science. This decline in climatic CO2 would have been accompanied by a cooling of the international environment, she included, most likely tipping Earth over a limit and permitting ice sheets to form.

There was likewise most likely localized cooling on the Antarctic continent due to plate tectonicsWolff stated. Around this time, South America and Antarctica lastly apart, opening what’s now the Drake Passage.

“This caused what we call a circumpolar present– water going right around Antarctica in a circle,” Wolff stated. “This isolates Antarctica from the remainder of the world and makes it much harder for warm air masses to make clear the Southern Ocean and, for that reason, makes Antarctica chillier.”

Plate tectonics likewise straight affected co2 levels, he included. Rock weathering and volcanic activity are both part of the carbon cycle, so over countless years, geological procedures can move the balance of gases in the environment.

Some unpredictability stays, scientists are relatively positive about this shift 34 million years ago thanks to the chemical signatures in rock sediments. Oxygen atoms exist in 2 kinds: oxygen-16 (typical oxygen) and oxygen-18 (heavy oxygen). Continental ice consists of a greater percentage of the lighter oxygen-16, indicating the oceans– and, for that reason, the shells of little sea animals– consist of a greater portion of oxygen-18 when ice sheets are larger.

“By taking a look at the oxygen isotopes in the carbonate shells of little sea animals in ocean sediments, you see a dive around 34 million years back, which individuals take as being due to the fact that the [lighter] oxygen isotope is going onto the continent of Antarctica,” Wolff discussed.

When it comes to whether Antarctica might ever be ice-free once again, “It’s absolutely possible, van de Flierdt stated.”World Earth has actually done it in the past. World Earth might do it once again.” While it’s not likely that human activity will cause the total melting of the ice sheet, it’s crucial we do whatever possible to restrict the loss of ice from the Antarctic now, she included. “It’s in our hands to prevent the worst-case circumstance,” van de Flierdt stated.

Victoria Atkinson is a freelance science reporter, focusing on chemistry and its user interface with the natural and human-made worlds. Presently based in York (UK), she previously worked as a science material designer at the University of Oxford, and later on as a member of the Chemistry World editorial group. Considering that ending up being a freelancer, Victoria has actually broadened her focus to check out subjects from throughout the sciences and has actually likewise dealt with Chemistry Review, Neon Squid Publishing and the Open University, among others. She has a DPhil in natural chemistry from the University of Oxford.