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.
Based on the analysis of some of the oldest continental rocks found onresearchers have proposed that the production of was initiated under the influence of large meteorite impacts on the young Earth, which was then occupied by .
A cycle of continental growth based on the duration of a galactic year
A new study completes this hypothesis. By studying the isotopic composition ofIs found in from Greenland and the Pilbara (Australia), the researchers discovered that the formation period of the first continents varied from -2.8 to -3.8 billion years. But would have occurred intermittently and cyclically. A peak in the production of continental crust is actually observed approximately every 200 million years. Digging into the data page the researchers found that this repetition strangely corresponds to the phases of from across . This transit could be like a galactic year in a way. Her estimated to be 225-250 million years old.
In fact, our solar system as well as the spiral armsrevolve around the middle of in a huge circular, but at various! When the spiral arms rotate at a speed of 210 km/sec and His 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. However, this one is surrounded by a comet, . For scientists, it causes a disturbance to the solar system when the solar system enters a new galactic arm. .
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 dispersedin the solar system, which leads to an increased risk of impacts on the planets and especially the Earth. These would also arrive with one higher than those of the bodies from which . On the young Earth, these powerful impacts would thus have had the capacity to produce a greater amount of magmatic, by brutal decompression of . These molten rocks, enriched with light elements such as silica, that and would then rise to the surface and form a kind of proto-crust that floats on the surface of the ocean from primitive. These of crust would be in the origin of the first .
To’Phil Sutton, co-author of the study, the results of which appeared in the journal , 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 bypublished on August 13, 2022
If todayand 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 that the first continental crust formed, giving rise to the first . Although 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 established. in which the subductions participate . However, we did find some 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, 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. IN however, 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. After analyzing the chemical composition of zircons, and especially the proportions of the different 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 bygiants, like the one that billions of years later caused . 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.