Antarctica, once a temperate, green continent, froze roughly 34 million years ago and became covered by the thickest ice sheet on the planet, reaching up to five kilometers deep in some areas. Meanwhile, on the other side of the world, the Arctic stayed ice-free for another 25 million years.
This time gap between the North and South Poles has puzzled scientists for a long time, but a new study published in the journal Science appears to have solved the mystery.
Antarctica froze first, the researchers write, because of a geological process that had begun tens of millions of years earlier and eventually formed the massive Gamburtsev Mountain Range in East Antarctica. That high elevation allowed ice to gradually build up at a time when Earth’s average temperature was five degrees Celsius higher than it is today.
Antarctica was once part of the southern supercontinent Gondwana, which also included Africa, South America, Australia, Arabia and the Indian subcontinent. It began breaking apart due to tectonic activity around 160 million years ago, a shift that eventually cooled temperatures across the planet.
According to the study, Gondwana’s breakup triggered waves in Earth’s mantle, disturbances that travel slowly through the planet’s deep interior. When these waves reached Australia millions of years later, the researchers say, they stripped material from the underside of the newly formed continent, making it lighter. This caused the land to rise, forming the Gamburtsev Mountains, which stand over 3,200 meters tall but today lie completely buried under ice. The cold typical of high elevations, the researchers say, kept snow from melting and allowed the ice to become permanent.
The situation was completely different in the Arctic, where glaciers formed and retreated over the past 50 million years without ever forming a permanent ice sheet. That only happened around 10 million years ago, when temperatures finally dropped low enough to allow ice to build up on the surface of the Arctic Ocean.
Today, the polar ice caps are under threat from human-driven climate change. Some studies don’t rule out the collapse of ice in parts of East Antarctica, which holds enough water to raise sea levels by more than 50 meters over the course of a few centuries.
