Published: Thu, January 23, 2020
Sci-tech | By Patricia Wade

World's oldest asteroid strike identified in WA

World's oldest asteroid strike identified in WA

An innocuous crater in Yarrabubba, Western Australia has been identified as the oldest known extraterrestrial impact site on Earth, with researchers calculating that the natural structure dates back a whopping 2.229 billion years. But its true age was not known.

"After the impact, glacial deposits are absent in the rock record for 400 million years".

"Yarrabubba, which sits between Sandstone and Meekatharra in central WA, had been recognised as an impact structure for many years, but its age wasn't well determined", Professor Kirkland said.

"The timing raised the possibility that the Earth's oldest asteroid impact may have helped lift the planet out of a deep freeze", said Curtin University's Professor Chris Kirkland.

"The effects of impact cratering have always been recognised as drivers of climate change", the study said. Could this asteroid have been the violent geological event needed to knock Earth out of this ice age gridlock?

The authors of the new study wrote that such "extraterrestrial bombardment" likely had major consequences for Earth's development throughout history - if the meteors hit certain parts of the planet. Large impacts leave behind scars the size of a small city.

The team from Curtin University in Perth used isotopic analysis of minerals to calculate the precise age of the 43-mile-wide impact crater for the first time. After impact, the isotopic clocks start ticking again as new lead accumulates.

They then analysed the amount of uranium and lead in the minerals found in those samples.

These simple bacteria had already begun changing the composition of air.

A huge impact crater in Australia has been confirmed as the world's oldest, and it could throw light on rapid ancient climate change.

As oxygen levels built up, rocks started weathering more, and the atmosphere cooled down.

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In turn, this might have triggered or contributed toward global warming - and the end of Snowball Earth.

Earth has repeatedly dipped into glacial conditions over the last 4.5 billion years. "We just don't know the answer to that yet".

Geochemist Christian Koebel of the University of Vienna who was not involved in the study tells The New York Times that extrapolating past climatic events from current data is "where things get a lot more speculative".

We may owe our existence to this Snowball Earth event.

In these periods, ice forms from the poles well into the tropics, covering almost all of Earth.

Oldest impact?Looking out across the structure from Barlangi Rock, which is a hill of impact melt near the crater centre.

At that time, most land was clustered around the equator, but the glaciers left their mark on the rocks even there.

The planetary cooling was so extreme that it left the Earth nearly completely covered by ice sheets. We also know Earth had ice at the time, but not how much.

Using a computer simulation, Erickson and his team modeled the atmospheric effects of the asteroid collision, finding that vaporized ice could cause "between 9×10 and 2×10kg of water vapour being jetted into the upper atmosphere within moments of the impact", according to the study. As it turns out, it's quite a lot. Calculations indicated that an impact into an ice-covered continent could have sent half a trillion tons of water vapor - an important greenhouse gas - into the atmosphere. It's responsible for about half of the heat absorption from solar radiation today.

During roughly the same time period, the Earth significantly cooled. Read the original article.

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