Earth’s Oldest Rocks Were Likely Formed By Meteorite Impacts

Posted: Aug 14 2018, 5:06am CDT | by , Updated: Aug 14 2018, 5:19am CDT, in News | Latest Science News

 
Earth’s Oldest Rocks were Likely Formed by Meteorites
Credit: Smithsonian National Museum of Natural History

New study says that oldest Acasta felsic rocks could have been formed at low pressures and very high temperatures

The rocks found at Acasta River in Canada are the oldest known rocks on Earth. These rocks are 4.02 billion years old and have barely changed since their formation which allows researchers to unlock their secrets. The Acasta rocks are significant not only for their age but also for their composition, which mainly involves silica-rich felsic.

Scientists have long known that the the felsic rocks in Acasta are different from majority of felsic rocks we see today. When a combined team of researchers from Australia and China modeled the formation of the oldest Acasta felsic rocks, they found that these rocks could have only been formed at extreme pressures and very high temperatures.

“Our modelling shows that the Acasta River rocks derived from the melting of pre-existing iron-rich basaltic rock, which formed the uppermost layers of crust on the primitive Earth.” Lead author of the study Tim Johnson from Curtin University at Perth said.

Acasta rocks are located at a surprisingly shallow depth of the planet’s crust. The heat required for melting at such shallow reveals something unusual about their formation – the source must be incredibly powerful, which hints at meteorite bombardment or impact.

“We used phase equilibria and trace element modelling to show that the Acasta River rocks were produced by partial melting of the original mafic rocks at very low pressures. It would have needed something special to produce the 900 °C temperatures needed to generate these early felsic rocks at such low pressures, and that probably means a drastic event, most likely the intense heating caused by meteorite bombardment.” Tim Johnson said.

Researchers suggest that felsic rocks would have been very common on Earth's ancient crust, but over the course of 4 billion years, they sunk back into the planet's interior due to the action of plate tectonics. Acasta rocks, which may have formed not long after Earth's formation, are possibly the only surviving remnants of meteorite impacts.

“The idea of making felsic melts by large or giant impacts seems plausible considering the high-energy nature of these events and the pockmarked ancient surfaces of other inner Solar System planets and moons,” said Dr. Balz Kamber from Trinity College Dublin. “However, the implied pressure-temperature regime might also permit melting of shallow crust below a super-heated impact melt sea. In other words, an indirect consequence of the impact itself".

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<a href="/latest_stories/all/all/47" rel="author">Hira Bashir</a>
The latest discoveries in science are the passion of Hira Bashir (). With years of experience, she is able to spot the most interesting new achievements of scientists around the world and cover them in easy to understand reporting.

 

 

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