Giant asteroids at the origin of the continents?

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

The question of the formation of the first continents is still and always much debated. In question, the difficulty of finding elements that date back more than 4,000 million years. However, a new study has updated the hypothesis of an origin linked to major meteorite impacts. You may also be interested.
[EN VIDÉO] A billion years summarized in 40 seconds: plate tectonics Researchers have modeled the movements of tectonic plates over the past billion years. If today the amount of continental crust remains relatively stable and represents around 30% of the earth’s surface, it has not always been this way. Originally, our planet consisted only of a large ocean of magma. It was from this ocean of molten rock that the first continental crust was formed, giving rise to the first continents. If today we know that continental growth is mainly associated with the volcanism of subduction zones, the mechanisms involved in the formation of the first continental masses are still not clearly determined, plate tectonics in which subductions take part being non-existent before 3,800 millions of years does. However, certain minerals typical of the continental crust, zircons, have been found, which have a much older age: more than 4,000 million years. Several theories to explain the formation of the first continental crustThere are therefore several theories to explain the formation of the first continents. of the primitive magma ocean. Some scientists suggest that it all began with the formation of a protocrust with a composition very different from that of our present continents, but which could have served as a “base” for the generation of the first continental crust. Others involve giant meteorite impacts. Although proposed several decades ago, this second hypothesis had never been clearly supported by solid evidence. In a new study published in Nature, a team of scientists from Curtin University (Western Australia), however, manage to bring this theory up to date by providing new elements. Were the first continental rocks formed under the heat of meteorite impacts? with other studies on the origin of the first continents, Tim Johnson and his colleagues built on the study of zircons from the Pilbara Craton in Western Australia. Cratons are, in fact, the oldest regions on Earth and the most likely to contain traces, albeit extremely faint, of the origin of the first continental crust. After analyzing the chemical composition of the zircons, and in particular the ratios of different oxygen isotopes, 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 in agreement with the effect produced by a large meteorite impact, subsequently, the disappearance of the dinosaurs. These types of catastrophic events were not uncommon 4 billion years ago. Back then, the Earth was still very heavily bombarded. The scientists now want to strengthen their theory by analyzing zircons from other regions of the globe, in order to show that it really would be a global mechanism and not a local specificity. did you just read
#Giant #asteroids #origin #continents

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