Here's why the South Pole froze over before the North Pole

Scientists say they may have solved a long-standing mystery about why Antarctica became covered in permanent ice around 34 million years ago, while the Arctic remained largely ice-free for another 25 million years.

A new study published in the journal Science found that a powerful geological process beneath Earth's surface lifted eastern Antarctica high enough for glaciers to form and expand, allowing a permanent ice sheet to develop even when global temperatures were about 9 degrees Fahrenheit (5 degrees Celsius) warmer than they are today.

Researchers analyzed Antarctica's ancient landscape and used computer models to reconstruct how the continent evolved over millions of years. They discovered that slow-moving disturbances deep within the Earth's mantle, known as mantle waves, caused the uplift of the Gamburtsev Mountains beneath eastern Antarctica.

According to the researchers, the rising landscape eventually reached a critical elevation that allowed snow and ice to remain year-round, leading to the formation of the massive East Antarctic Ice Sheet during the transition from the Eocene to the Oligocene epoch about 34 million years ago.

The study's co-leader, geoscientist Thomas Gernon of the University of Southampton, said the geological process began more than 160 million years ago during the breakup of the ancient supercontinent Gondwana, which once connected Antarctica with Africa, South America, Australia, Arabia, and the Indian subcontinent.

As these landmasses gradually drifted apart through plate tectonics, mantle waves reshaped Antarctica's landscape by removing dense rock beneath the continent, making it lighter and causing it to rise.

The researchers found that by about 45 million years ago, large parts of eastern Antarctica had risen above the elevation needed to support permanent ice. By around 34 million years ago, nearly 90% of the Gamburtsev Mountain region was above this threshold, compared with only about one-third of the area 60 million years earlier.

Study co-leader Thea Hincks said the findings highlight the importance of both climate and topography in determining when large ice sheets can form.

The Arctic followed a different path. Although glaciers advanced and retreated over the past 50 million years, permanent ice sheets did not become established until less than 10 million years ago because the North Pole lies in the middle of the Arctic Ocean rather than on high land.

Without elevated terrain, scientists said the Arctic required a much cooler global climate and lower atmospheric carbon dioxide levels before permanent ice could develop.

The findings help explain why Antarctica became Earth's first permanently ice-covered polar region and offer new insights into the geological and climatic processes that shaped the planet's modern climate system. 

-Reporting by Will Dunham in Washington; Editing by Daniel Wallis/Reuters