Scientists might have finally worked out how Antarctica was rapidly buried in a thick sheet of ice 34 million years ago. They believe that two factors contributed to glaciation of the southernmost continent. Their research is published in Nature Geoscience.

The Drake Passage (the region between South America and Antarctica) deepened, changing how water circulated in the oceans globally. The change shifted the direction of the warmer currents coming from the tropics, which were directed to northern latitudes.

The other contribution comes from the reduction of carbon dioxide in the atmosphere. CO₂ levels have been declining since the beginning of the Cenozoic Era 66 million years ago, but the sudden change in the ocean current led to more rain, which brought CO₂ below the critical value. This mean't Antarctica became frozen.

"It's an interesting lesson for us when it comes to climate change because what we get is a thumbnail shift between two stable climatic states in Antarctica – from no glaciers to glaciers,” said co-author Dr. Galen Halverson, from McGill University, in a statement. “And what we see is both how complex climate changes can be and how profound an effect changing patterns of ocean circulation can have on global climate states, if looked at on a geological time scale."

The two factors were seen before as competitive explanations for the frosting of the South Pole, but the researchers realized they were two sides of the same coin.

According to the scientists, the deepening of the Drake Passage started the powerful Antarctic Circumpolar Current. The looped current kept the cooler water near the continent and acted as a barrier from the warmer, less salty waters from the North Atlantic and Central Pacific.

Those currents were redirected towards the other continents, increasing rainfall. Rainfall increases the amount of weathering of rocks, a process that slowly traps the atmospheric CO₂ inside limestone.

The researchers think that nobody considered combining the two ideas before because they happen on different timescales. Currents change over thousands of years, while rock weathering happens over hundreds of thousands of years. But once combined, they were probably enough to bury Antarctica in ice and snow.