Scientists have identified a dome, rather than a crater, at least 50 km across, buried under the Timor Sea.

It was created by a giant asteroid smashing into the Earth around 35 million years ago -- a period of heavy extraterrestrial bombardment.

These findings by Australian National University (ANU) geologists could suggest a link between these impacts and a sharp fall in global temperatures preceding the formation of the Antarctic ice sheet.

Seismic surveys in areas straddling the Ashmore Platform and Browse Basin led oil company geologist Dariusz Jablonski of Finder Exploration to suspect the large impact.

Andrew Glikson, who specialises in the study of extraterrestrial impacts, from the Planetary Science Institute at ANU, was asked to study cuttings from the Mount Ashmore-1B well.

“The minimum size of the Mount Ashmore dome, which represents elastic rebound doming of the Earth crust triggered by the impact, is 50 km at the base, but the full size of the impact crater - not yet defined - may be significantly larger,” Mr. Glikson said.

Mr. Glikson said the period when the asteroid hit coincided with a time of heavy asteroid bombardment of the Earth, which may have played a role in the sharp drop in global temperatures at the time.

“Round the same time as the Mount Ashmore impact, a 100 km wide asteroid impact structure formed in Siberia, and another measuring 85 km in diameter in Chesapeake Bay, off Virginia, in the United States.”

“Likewise a large field of tektites - molten rock fragments splashed by impact - fell over northeast America. This defined a major impact cluster across the planet,” he said, according to an ANU release.

Mr. Glikson said the increase in geophysical surveys and drilling associated with oil exploration over the last few decades has allowed the identification of a number of large impact structures onshore and off the coast of Western Australia.

These findings have been published in the Australian Journal of Earth Sciences.

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