Scientists find evidence of oldest impact structure on Earth

James Marshall
January 22, 2020

The impact occurred around the time of a warming period and the end of a planet-wide ice age.

The Earth has a continually changing surface due to tectonics and erosion, which means that very old impact craters are hard to identify, the study said. That's half as old as the Earth itself. The timing of Yarrabubba's impact coincides with the formation of some of Earth's earliest icecaps and glaciers, shortly after the emergence of oxygen in the atmosphere.

"The impact event itself might not have been the full reason for a global climate shift, but if we are in a dynamic period of Earth's history when other things are happening this might have been the straw that broke the camel's back", co-author Chris Kirkland, a geologist at Australia's Curtin University, told the Australian Broadcasting Corp.

Nobody knows what caused the Earth to freeze, but once it did, the shiny white surface of the ice reflected heat and maintained the "snowball" conditions, until Carbon dioxide released by volcanoes created a greenhouse effect strong enough to melt the ice.

The researchers noted that the impact's correlation with melting glaciers in the same era would prompt further study into the effect of meteorites on the environment.

Till now, the oldest asteroid impact on Earth was the Vredefort Dome in South Africa.

But scientists are now excited by the "twist of fate" brought about by the Yarrabubba asteroid strike. For instance, after the impact, glacial deposits are absent in the rock record for 400 million years.

Dr Thomas Davison of Imperial College London, who co-authored the study, added: "Snowball Earth ended at nearly the same time as the Yarrabubba impact".

Considering the size of the Yarrabubba crater, researchers estimate that the impact released as much as 11,000 trillion pounds of water vapor into the atmosphere.

"These are all big questions in the field of science".

Although the original impact crater measured 43.5 miles (70km) across, only a 12.4-mile-wide (20km) section remains hidden away in the Australian outback.

They were able to identify specifically the exact origin of the crash by extricating zircon and monazite samples from the site's base which we were crystallised by the impact between the space rock and the ground.

The minerals are crystals of lead and uranium than can be dated under an electron microscope.

Dr Aaron Cavosie from Curtin University said: "Our findings highlight that acquiring precise ages of known craters is important - this one sat in plain sight for almost two decades before its significance was realised".

The Yarrabubba impact structure is regarded as one of Earth's oldest, but until now lacked a precise age.

Other reports by Click Lancashire

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