The question of the formation of the first continents is still hotly debated over and over again. The question is the difficulty of finding elements that are more than 4 billion years old. However, a new study has updated the hypothesis of an origin linked to large meteorite impacts.
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If today the amount of continental crust remains relatively stable and accounts for about 30% of the earth’s surface, this was not always the case. Originally, our planet was just a vast ocean of magma. From this ocean of molten rock formed the first continental crust, giving rise to the first continents. If we now know that continental growth is mainly related to the volcanism of subduction zones, the mechanisms involved in the formation of the first continental masses are still not unequivocally determined, since plate tectonics, in which subductions are involved, predate 3.8 Didn’t exist billions of years ago. However, certain minerals typical of the continental crust have been found, zircons, much older: more than 4 billion years.
Several theories to explain the formation of the first continental crust
So there are several theories that explain the formation of the first continents from the ocean of primitive magma. Some scientists suspect that it all started with the formation of a protocrust, the composition of which is very different from that of our modern continents, but which could have served as the “base” for the formation of the first continental crust. Others involve huge meteor impacts.
Although this second hypothesis has been proposed for several decades, it has never been unequivocally supported by any solid elements. However, in a new study published in Nature, a team of scientists from the University of Curtin (Western Australia) updates this theory 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 drew 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, albeit extremely faint, traces of the origin of the first continental crust. After analyzing the chemical composition of zircons, and in particular the proportions of the different oxygen isotopes, the researchers suspect that the first continental rocks formed from an episode of surface melting that progressed at depth, and not the other way around. However, this discovery is consistent with the effect of a large meteorite impact.
The formation of the first continental rocks may therefore have been triggered in regions struck by giant meteorites, like the one that caused the dinosaurs to disappear billions of years later. This type of cataclysmic event was anything but rare 4 billion years ago. At that time the earth was still being bombed very intensively.
The scientists now want to substantiate their theory by analyzing zircons from other regions of the world to show that it is indeed a global mechanism and not a local peculiarity.
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