New Crater May Have Helped Create Antarctic Ice Sheet

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An enormous impact dome has been discovered lounging idly under the Timor Sea. The approximately 50 kilometer-wide (31 mile-wide) dome is evidence that a huge asteroid collided with the Earth around 35 million years ago.

But this space rock wasn't alone. Numerous impact structures from the same time period are speckled across the planet. From the 85 kilometer-wide (53 mile-wide) impact basin in the Chesapeake Bay off the Virginia coast to a 100 kilometer-wide (62 mile-wide) impact in Siberia and bits of debris scattered like buckshot across much of North America, there is evidence that a huge swath of the globe was pelted by extraterrestrial material. 

In fact, scientists believe the slew of impacts joined forces to cause a drop in global temperature that occurred shortly after. 

About a million years after the shotgun blast of impacts, the Drake Passage — the ocean gap between Antarctica and South America — formerly sealed shut, opened up, said Andrew Glikson, of the Australian National University.

The rush of water through Drake Passage isolated Antarctica's climate from the rest of the globe, and fostered the growth of a large ice sheet which today still acts as a ‘thermostat’ for Earth’s climate, Glikson explained. 

But the cooling caused by the impacts may have gotten things started, chilling the planet down enough to get ice formation started. The study is featured in the new issue of the Australian Journal of Earth Sciences.

While the dome, named Mount Ashmore, is around 50 kilometers in diameter, the entire impact crater could be much larger, said Dr. Glikson. Determining the actual size of the impact crater — and thus the event itself — will go a long way toward pinning down how dramatic and widespread the effects of the impact were.

Impact structures come in all shapes and sizes. The Australian impact is a big one. Smaller impacts only create an impact crater. Meteor crater in Arizona is a good example

But during larger impacts, something different may happen: an impact dome or central peak rises up in the middle of the crater.

In the case of Mount Ashmore, rock rebounded upwards at the point of impact, compensating for the huge compressive punch of energy delivered in collision. Whether or not it also altered the course of global climate remains an intriguing mystery.

Image: Glen Dillon, Wikipedia 

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