When Antarctica separated from Africa during the breakup of the supercontinent Gondwana 160 million years ago, this rift did more than just split the continents apart. According to a study published in the journal Science, it may have also triggered slow-moving disturbances deep within the planet, eventually leading to the formation of mountains in East Antarctica. This uplift, in turn, could solve a long-standing puzzle: how did Antarctica’s massive ice sheet begin to take shape?
In the past, geologists believed that the effects of continental rifting were confined to the fault itself, where the Earth’s crust stretches and volcanoes erupt. However, recent research suggests that rifting can also generate waves deep within the hot rocks of the mantle. These waves travel slowly beneath the continents over millions of years. As they pass, they strip away dense rocks from the base of the continent, causing it to rise like a buoy. “This is a very slow process,” says Thomas Gernon, a geologist at the University of Southampton who led the study. “It’s like a chain reaction.”
Over the past several years, Gernon and his colleagues have been developing this idea—essentially an extension of plate tectonic theory—arguing that mantle waves could explain geological mysteries far from active plate boundaries, including puzzling volcanic eruptions and elevated plateaus in the interiors of continents. Now, they have used it to explain the mysterious origins of the Antarctic ice sheet.
Geological evidence indicates that the ice formed 34 million years ago, even though global temperatures and atmospheric greenhouse gas concentrations were higher than they are today. Comparable ice sheets in the Northern Hemisphere did not appear until 20 million years later, when greenhouse gas levels dropped and the planet cooled.
One possible explanation is that Antarctica had an advantage: its elevation above sea level. But for decades, scientists had only a vague understanding of the land buried beneath several kilometres of ice. Antarctica was often called the “pole of ignorance,” says Mathieu Morlighem, a glaciologist at Dartmouth College. However, over the last 15 years, organizations such as the British Antarctic Survey (BAS) and NASA have funded surveys using aircraft equipped with ice-penetrating radar. BAS combined all known profiles into a comprehensive map, revealing a rugged terrain, including the Gamburtsev Mountains—a mountain range hidden beneath the ice in East Antarctica. The images are now good enough to “build geological arguments from,” Morlighem says.
These mountains are difficult to explain. They rise deep in the heart of the continent, far from tectonic boundaries, and their sharp relief suggests they were exposed for only a short time before being shielded from erosion by layers of ice. Using a range of geodynamic models, Gernon and his colleagues found that mantle waves triggered by the breakup of Gondwana reached East Antarctica 50 million years ago, lifting the Gamburtsev Mountains by more than 1 kilometre over the following 15 million years. Evidence of an initial surge of erosion from the steep mountains appears in sediments formed along the coast around that same time, says John Goodge, a geologist at the University of Minnesota Duluth. “This happens at a specific time.”
The researchers then combined data on the history of crustal uplift with climate and ice sheet models. The results show that the rising landscape allowed isolated alpine glaciers to form in high-altitude areas, such as the Gamburtsev Mountains, while the continent remained much warmer than it is today. By 40 million years ago, as crustal uplift continued and temperatures slowly declined over a long period, a vast elevated region had formed in East Antarctica where snow could persist year-round, providing a foundation for the continent’s ice sheet. “This is a critical threshold in our models—this is where the snowline was,” Gernon says.
The new study outlines a plausible mechanism that no one had considered before, while still leaving room for the broader cooling trend, according to Goodge. “To me, it’s very convincing.”
However, mantle waves may not tell the whole story. A study recently published in Nature Geoscience found evidence that part of East Antarctica underwent an unusual form of tectonic stretching called rotational extension, in which the Earth’s surface is pulled apart like an unfolding paper fan. The cause and timing of this process are unclear, but “once you see it, you can’t unsee it,” says Jacqueline Austermann, a geodynamicist at Columbia University.
Although such stretching creates deep basins, it can also compress the crust along its margins. Since the Gamburtsev Mountains are located near one of these margins, it is possible that both stretching and mantle waves contributed to the uplift of the land on which the world’s largest ice sheet formed, says Egidio Armadillo, a geophysicist at the University of Genoa, who led the Nature Geoscience study. “Usually, the real world is much more complicated than our simple models.”
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