The formation of continental crust on Earth can be linked to the movements of the Solar System in the Milky Way

Une nouvelle étude relance l'hypothèse que les premiers continents auraient été créés à la suite d'impacts géants, en apportant de nouveaux éléments. © sdecoret, Adobe Stock

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How did the first continents form? In a previous article (read below), Futura described the debate currently animating the scientific community about this question. Although there are many theories, one involving a meteorite impact was published in a journal article a few weeks ago. Nature.

Based on the analysis of some of the oldest continental rocks available EarthResearchers have actually proposed the production of Continental crust Then the occupied young Earth was launched under the influence of large meteorite impacts A great ocean of magma.

A cycle of continental growth modeled on a galactic year

A new study complements this hypothesis. By studying the isotopic composition Zircons found in Cratons From Greenland and the Pilbara (Australia), the researchers found that the first continents formed between -2.8 and -3.8 billion years ago. But Development of continents Intermittently cycled. A production peak Continental crust Observed approximately once every 200 million years. Drilling down on the data side orbitsThe researchers found that this recurrence strangely corresponds to the phases Transportation from The Solar System throughout The four main spiral arms of our galaxy. This transit can be like a galactic year in a way. her Duration Estimated to be 225-250 million years old.

Indeed, our solar system and its spiral arms milky way revolves around the center Galaxy On a large scale Movement round, but at Gears Different! As the spiral arms rotate at a speed of 210 km per second, the the sun And his Collaboration The planets, including the Earth, move at a maximum speed of 240 km/s. This change has a major effect: the solar system thus crosses the four galactic arms at regular intervals. However, it is surrounded by a cometary cloud, Called Oort Cloud. For scientists, when the solar system enters a new galactic arm, it causes a disturbance Cloud of Oort.

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The arrival of comets at the time of entering a new arm of the galaxy

In this case, the frozen cometary bodies are then dispersed Mass Impacts on the solar system, the planets, and especially on Earth, lead to increased risk. These are Comets Comes with a Energy Higher than the bodies that come from Asteroid belt. On a young Earth, these powerful influences would have been highly productive Liquid Magmatic, by brutal decompression Code. These molten rocks are enriched with light elements such as silica,AluminumThe Sodium And this PotassiumIt then rises to the surface, forming a kind of proto-crust that floats on the surface of the ocean Magma Ancient. These are embryos The crust is the first appearance Continent masses.

for thisAstrophysicist Bill Sutton, co-author of the study, whose results appeared in the journal Geography, This hypothesis deserves further investigation. ” We want to make that connection and start a conversation to look beyond Earth, beyond the solar system, to look at geological processes and what drives them. We did not evolve in isolation. »

The hypothesis shows how forces external to our planet and our solar system may have influenced Earth’s topography. However, this idea is difficult to prove and the number of arguments is very limited 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. Questionable is the difficulty of finding elements dating back 4 billion years. However, a new study brings to date the hypothesis of an origin linked to large meteorite impacts.

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The article Morgan Gillard Published on August 13, 2022

If today The volume of continental crust remains relatively constant And reflecting about 30% of the Earth’s surface, it’s not always there. Originally, our planet was composed of a vast ocean of magma. It is from this rocky sea Connecting The first continental crust formed, leading to the first appearance Continents. If we know today that continental growth is mainly related to the volcanism of zones subjugationThe mechanisms involved in the formation of the first continental masses are not yet clearly determined Tectonic plates Vice-Chancellors participate in this Existed 3.8 billion years ago. However, we found a few Minerals Continental crust, typical of zircons, shows a much older age: more than 4 billion years.

Several theories explain the formation of the first continental crust

There are several theories to explain the formation of the first continents from a primordial magma ocean. Some scientists suggest that it all starts with practice A proto-crust of a composition very different from that of our present continents, but it may have served as the “base” for the generation of the first continental crust. Others involve giant meteor impacts.

Although proposed for decades, this second hypothesis is not clearly supported by the evidence Solid. In A new study has been published NatureA team of scientists from Curtin University (Western Australia) brings this theory up to date by providing new elements.

The first continental rocks formed under the heat of a meteorite impact?

As with other studies of the origin of the first continents, Tim Johnson and his colleagues based their study on zircons from the Pilbara Craton in Western Australia. Cratons are actually the oldest parts of the Earth and contain traces of the first appearance, albeit very small Continental crust. After analyzing the chemical composition of zircons, especially the different proportions Isotopes Oxygen, the researchers suggest, would have formed from an episode of surface melting in which the first continental rocks progressed to depth, but not the other way around. However, this finding is consistent with the effect of a large meteorite impact.

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So the formation of the first continental rocks may have started in the affected areas Meteorites The giants, just as they caused, billions of years later, the The extinction of the dinosaurs. This type of cataclysmic event was rare 4 billion years ago. Even then the Earth was heavily bombarded.

The scientists now want to strengthen their theory by analyzing zircons from other parts of the world to show that this is indeed a global mechanism and not a local specificity.

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