Once upon a time, the Arctic was a landmass three times the size of Antarctica. Approximately 200 million years ago, it contributed to a cooling trend that lasted for millennia and gave dinosaurs the opportunity to conquer the planet.
According to paleontologist Paul Olsen from Columbia University in New York, this “giant Arctic continent” encompassed the territory of present-day Siberia and China.
For the majority of the Mesozoic Era—from 252 to 66 million years ago—all the Earth’s land was fused into a single supercontinent, Pangaea, with the exception of what was then thought to be the area of modern China. This block of continental material was divided into two fragments that drifted at a moderate latitude in the world’s sole ocean at the time, named Panthalassa.
Nevertheless, recent geological analysis, incorporating the magnetic signatures of rocks which allow for the reconstruction of their ancient formation latitudes, led Olsen and other researchers to the conclusion that both Mesozoic Chinese fragments were actually connected to Pangaea. Furthermore, the entire configuration of continents was oriented so that Siberia and China collectively occupied a large portion of the North Polar Circle.
This arrangement helps piece together parts of the climatological and biological puzzle, Olsen will explain at the annual assembly of the European Geosciences Union in Vienna next month.
During the Mesozoic, the climate was considerably warmer than it is today. But 201 million years ago, at the conclusion of the first Mesozoic period, known as the Triassic, Pangaea began to fragment, giving rise to the Atlantic Ocean. The intense volcanism accompanying this breakup coincided with a period of global cooling, sea-level drop, the extinction of many large animals, and the emergence of dinosaurs. However, the connection between all these events remained somewhat obscure.
Olsen posits that the Arctic continent played a crucial role. Firstly, even in a warm global climate, the vast area surrounding the North Pole would have experienced winters covered in snow and ice. Such frozen landscapes possess high albedo, meaning they reflect a relatively large portion of the planet’s solar heat and light.
The vital point is that when aerosols injected into the atmosphere by intense volcanic activity chilled the climate, this suppressed summer melting in the far north, allowing ice to persist and consequently reflect sunlight year-round. “High summer albedo would have amplified the lack of melt, and through this feedback mechanism, you could achieve a much longer period of truly cold conditions and possibly a temporary polar ice cap that could endure for millennia,” Olsen states.
The accumulation of ice in the Arctic accounts for the drop in sea level, and the sharp cooling induced by volcanic winters led to species extinctions. Some dinosaurs managed to survive the extinction event triggered by the global cooling because they inhabited the Arctic continent and had developed insulating plumage to endure the harsh winters there. Thus, when the entire Earth cooled, they were prepared to take over, according to Olsen.
“It’s a fascinating notion because we generally assume the Earth was ice-free for most of the Mesozoic,” remarks Mike Benton from the University of Bristol, UK. “To picture the early dinosaurs in a world with severe winters is novel, even if it was for a relatively brief time. It was an epoch of extinction and dinosaur fauna turnover, so the combination of volcanic eruptions and northern ice could have impacted them profoundly.”
Olsen suggests that the concept of a large Arctic continent has “been hiding in plain sight” for quite some time. “I think a large part of that is due to how scientists typically render global diagrams, where the poles are either infinitely stretched, like in a Mercator projection, or nearly invisible. Both scenarios tend to divert attention away from polar regions.”
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