2370°C would be the highest temperature the earth’s crust has ever known

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According to NASA, 84,000 meteorites hit the earth every year. We certainly know that the earth, bombarded by numerous meteorites in its youth, once experienced hellish temperatures. But until now we didn’t know to what extent. In 2017, a first study revealed that a meteorite impact 36 million years ago produced rock with a temperature of almost 2370 degrees Celsius. Recently, this measurement has been refined, and most importantly, the researchers confirmed that this rock witnesses the hottest zone ever discovered on Earth. It tells us a little more about the conditions that helped make our planet habitable.

The discovery of this rock dates back to 2011, during a Canadian Space Agency-funded study to coordinate the work of astronauts and rovers to explore another planet, or the moon, at the level of Mistastin’s crater — which closely resembles a lunar crater and is often used as a substitute for such research. The latter is located in northwestern Canada, in the Labrador region. It was formed about 36 million years ago when an asteroid hit it. It is almost 28km across and its center is now occupied by a 16km long lake in which floats a small island created by rebound after impact. Michael Zanetti, then a researcher at the University of Western Ontario, and his colleagues found a rock there, a striking glass containing small grains of zirconium.

Subsequently, this rock was analyzed in 2017, suggesting that it formed as a result of the impact at 2370 degrees Celsius. Additional studies had to be conducted to confirm or refute these initial findings. It is finished. The new study was published in Earth and Planetary Science Letters.

Zirconia, a high temperature recorder

To refine the first measurement, the researchers had to date more than one zircon. Indeed, the new team, led by Nicholas Timms of the University of Perth in Australia, was interested in the minerals found on the walls of the crater – their presence is as much indicative of an impact – and in zirconia in particular, especially zirconium oxide (ZrO2). After examining four other zircons in samples from the crater collected between 2009 and 2011, the authors found that this zirconia was in cubic crystalline form. These samples came from a variety of rock types in different locations and give a more comprehensive view of how the impact heated the ground. One consisted of glassy rock formed on impact, two consisted of rock that had melted and resolidified, and one consisted of sedimentary rock containing glass fragments formed on impact.

Black glass rock sample found in Mistastin Crater. © Gavin Tolometti

However, zirconia comes from the mineral zircon, which only becomes zirconia when exposed to a temperature of at least 2,370 degrees Celsius. Nicholas Timms then determined the age of this cubic zirconia with the help of his team. It would have appeared about 36 million years ago. The results confirmed that the high-impact glass zircons formed at a heat of at least 2,370 degrees Celsius, just as the 2017 research suggested. As an extremely durable mineral that crystallizes at high temperatures, the structure of zircons can reveal how hot it was when they formed. As Gavin Tolometti, a postdoctoral fellow at the University of Western Ontario and lead author, explains in a press release: No one before had even considered using zirconia as an impact melting temperature recorder. This is the first time we have evidence that real rocks can be this hot. “.

A new mineral in this region

The researchers also found a mineral called reidite in the crater’s zircon grains. This is the first time Reidites have been discovered on this site. These minerals form when zircons are exposed to high temperatures and pressures. Because of this, their presence allows researchers to calculate the pressure the rocks were subjected to during the impact. They found that the impact generated pressures of between 30 and 40 gigapascals.

Indeed, Tolometti says: ” Given the size of the Reidite in our samples, we knew the minimum pressure it registered was probably around 30 gigapascals. However, since there are still many reidites in some of these grains, we know they can be even higher than 40 gigapascals “. This gives a better idea of ​​how much pressure is being generated outside of the melt zone when the meteorite hits the surface. Since this would be pressure at the edges of the impact, the researchers believe that where the meteorite hits directly on the hit the crust, the rock would not only have melted but vaporized because the pressure was enormous.

Lake Mistastin in the crater and its island. © NASA Earth Observatory/Lauren Dauphin

Meteorites shape our world today

Beyond the record for “the highest temperature recorded in the Earth’s crust,” this research shows how a region can become hell immediately after a celestial body impacts. But, paradoxically, as the authors point out, life on this planet may owe much to these catastrophes. Mistastin’s, fairly recent and moderate, was fairly isolated.

But four billion years ago, during the great late bombardment, the impacts were incessant – it was hell on earth, a time called the Hadean. They played an important role in the formation and composition of the earth’s crust. They resurfaced the planet and helped make it habitable. In other words, the meteorites “cooked” the Earth’s crust — our soil — and then triggered a release of hydrogen, carbon, and sulfur into the atmosphere. These last elements are the origin of life on earth. However, had they been in abundance, they could have made our planet uninhabitable. Lucky combination of circumstances.

The research group plans to extend this work to other impact craters on Earth, such as Lake Wiyâshâkî (Clearwater West Crater) in Quebec. The researchers also hope to use similar methods to study rocks retrieved from impact craters on the moon during the Apollo missions. Tolometti summarizes: It could be a step forward in understanding how rocks were altered by impact craters across the solar system. “.

Source: Earth and Planetary Science Letters

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