The formation of continental crust on Earth may be associated with the movements of the solar system in the Milky Way

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How were the first continents formed? In a previous article (read below), Futura described the debate currently animating the scientific community on this issue. While several theories exist, the one involving a meteorite impact resurfaced with the publication a few weeks ago of an article in the journal Nature.

Based on the analysis of some of the oldest continental rocks found on the earthresearchers have proposed that the production of continental crust was initiated under the influence of large meteorite impacts on the young Earth, which was then occupied by a huge sea of ​​magma.

A cycle of continental growth based on the duration of a galactic year

A new study completes this hypothesis. By studying the isotopic composition of zircons found in the cratons of Greenland and Pilbara (in Australia), the researchers discovered that the formation period of the first continents was spread from -2.8 to -3.8 billion years. But the growth of the continents would have occurred intermittently and cyclically. A production peak on continental crust is actually observed approximately every 200 million years. Digging into the data page orbitalsthe researchers found that this repetition strangely corresponds to the phases of transit from Solar system across four primary spiral arms in our galaxy. This transit could be like a galactic year in a way. Her duration estimated to be 225-250 million years old.

In fact, our solar system as well as the spiral arms The Milky Way revolve around the middle of galaxy in a huge movement circular, but at gear various! When the spiral arms rotate at a speed of 210 km/sec Sun and His cohort planets, including Earth, pass at a higher speed of 240 km/second. This shift has a major consequence: the solar system thus crosses the four galactic arms at regular intervals. But this one is surrounded by a cloud of comets, called the Oort Cloud. For scientists, it causes a disturbance to the solar system when the solar system enters a new galactic arm. Oort cloud.

An influx of comets at the time of entry into a new arm of the galaxy

On this occasion, frozen cometary bodies would then be dispersed lot in the solar system, which leads to an increased risk of impacts on the planets and especially the Earth. These comets would also arrive with one energy higher than those of the bodies from which asteroid belt. On the young Earth, these powerful impacts would thus have had the capacity to produce a greater amount of liquid magmatic, by brutal decompression of Coat. These molten rocks, enriched with light elements such as silicaI’aluminumthat sodium and potassiumwould then rise to the surface and form a kind of proto-crust that floats on the surface of the ocean from magma primitive. These embryos of crust would be in the origin of the first continental masses.

To’astrophysicist Phil Sutton, co-author of the study, the results of which appeared in the journal Geology, this hypothesis deserves further investigation. ” We want to make that connection and start the conversation to look at the geological processes that are happening beyond Earth, beyond the Solar System, and what might be driving them. We did not just arise in isolation. »

The hypothesis shows how many forces outside our planet, and even our solar system, could have affected Earth’s landscape. But the idea seems difficult to prove and the number of arguments is still very thin at the moment.

Giant asteroids in the origin of continents?

The question of the formation of the first continents is still and always strongly debated. It is about the difficulty of finding elements that go back more than 4 billion years. However, a new study has updated the hypothesis of an origin associated with larger meteorite impacts.

Article by Morgan Gillard published on August 13, 2022

If today the amount of continental crust remains relatively stable and represents about 30% of the earth’s surface, it has not always been this way. Originally, our planet consisted of just one huge ocean of magma. It is from this sea of ​​stones in fusion that the first continental crust formed, giving rise to the first continents. If we know today that continental growth is mainly associated with the volcanism of the zones subductionthe mechanisms involved in the formation of the first continental masses are still not clearly established, the tectonic plates in which the subductions participate was non-existent until 3.8 billion years ago. However, we did find some minerals typical of continental crust, zircons, which show a much higher age: more than 4 billion years.

Several theories to explain the formation of the first continental crust

There are thus several theories to explain the formation of the first continents from the sea of ​​primitive magma. Some scientists suggest it all starts with exercise of a proto-crust of composition very different from that of our present continents, but which could have acted as a “base” for the generation of the first continental crust. Others involve giant meteorite impacts.

Although proposed for several decades, this second hypothesis had never been clearly supported by evidence solid. IN new study published in Naturehowever, a team of scientists from the University of Curtin (Western Australia) brings this theory up to date by providing new elements.

The first continental rocks formed under the heat of meteorite impacts?

As with other studies of the origin of the first continents, Tim Johnson and his colleagues based their work on the study of zircons from the Pilbara Craton in Western Australia. Cratons are actually the oldest regions on Earth and the most likely to contain traces, albeit extremely tenuous, of the origin of the first continental crust. After analyzing the chemical composition of zircons, and especially the proportions of the different isotopes oxygen, the researchers suggest that the first continental rocks would have formed from an episode of surface melting that progressed to depth, and not the other way around. However, this discovery is consistent with the impact of a major meteorite impact.

The formation of the first continental rocks could therefore have begun in the areas affected by meteorites giants, like the one that billions of years later caused the disappearance of the dinosaurs. This type of catastrophic event was far from rare 4 billion years ago. The earth was then still very intensely bombarded.

The researchers now want to strengthen their theory by analyzing zircons from other regions of the globe to show that it is indeed a global mechanism and not a local specificity.

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