2023-06-16 17:15:48
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[EN VIDÉO] Earth’s history seen from space Since the end of the Second World War, Man has gained height and…
Our Planet, as well as the Solar systemSolar system, was formed 4.6 billion years ago. This is a fact that is now consensus. However, one point remains hotly debated. That of the durationduration of this formation and the mechanisms associated with it. The most popular theory involves a phase of collisions between planetary embryos. It would thus have taken 50 to 100 million years to form the Earth in this way, because this theory implies a certain degree of chance. Yes, we do not cross paths with small planetoids every day.
A formation in just a few million years
But, in recent years, a new idea has made its way. That of a much faster formation, in just a few million years, and not involving giant impacts, but rather a accretionaccretion small elements of only a few millimeters. This theory was presented in an article published 3 years ago (read below). The Copenhagen researchers, authors of this previous study, are now returning to the subject to constrain the nature of the material at the origin of the telluric planetstelluric planets of the solar system, more particularly the Earth and Mars, and thus determine their mode of formation.
In a new article published in the journal Naturethe scientists used the isotopesisotopes of siliconsilicon as tracers to understand the mechanisms of planet formation. They thus analyzed the isotopic composition of more than 60 meteoritesmeteorites different and planetary bodies, in order to observe the link ” geneticgenetic that may exist between them.
Growth by dust accretion
The results show that, contrary to the most common idea, chondriteschondrites would not constitute the building blocks of planets like Mars and Earth. On the other hand, it appears that these two planets would have a link with asteroidsasteroids differentiated formed very early in the history of the Solar System. This suggests a rapid formation, in less than 3 million years, via a growth by collision and accretion of very small elements present within the proto-planetary disk. According to the researchers, a starstar a hundred kilometers in diameter can thus form very quickly from this disc of dust. Once reached this size, the growth continues by “aspiration” of all the elements present nearby, including small particles of ice.
The presence of water is no longer a matter of luck
This new vision therefore has a consequence on the origin of water on Earth. In the most common hypothesis, the water would indeed have been brought to Earth by the bombardment of comets rich in water ice at the end of the formation of the Planet. But the new theory proposed by the Copenhagen researchers, questioning the mode of formation of the Earth, implies that the accumulation of water was made during the phase of rapid accretion and therefore did not not a “distant” origin.
A consideration that is important because it dismisses the notion of “luck” implied by the hypothesis of water brought by cometscomets. The new theory suggests on the contrary that water is an element intrinsically linked to the formation of terrestrial planets, whether in our solar system… or elsewhere.
The initial phase of the formation of the Earth took place much faster than previously thought. It is by measuring with extreme precision the isotopes of ferfer that researchers have come to this conclusion.
Article of Nathalie MayerNathalie Mayerpublished on February 24, 2020
Random collisions of larger and larger bodies over several tens of millions of years. This is how the astronomersastronomers have long imagined that our Earth was formed. But research work from the University of Copenhagen (Denmark) are now questioning this theory. The whole thing would have been played out in just five million years.
Only ? Across theUniverseUniverse, there is no doubt. And even on the scale of our solar system. Its age is estimated at around 4.6 billion years. Bringing it all down to 24 hours, the Copenhagen researchers’ results suggest that it would have taken the proto-Earth just a minute and a half to form. Against five to fifteen minutes according to the idea hitherto accepted.
The work of researchers from the University of Copenhagen now directs astronomers more towards another theory. “As a starting point, there was dust. Millimetre-sized objects, raining down on a growing body and forming our Earth all at once”explains Martin Schiller, researcher, in a press release from the University of Copenhagen.
Water more mundane than expected?
This conclusion, the researchers draw it from the most precise measurements ever carried out on iron isotopes. They have indeed studied the isotopic mixture of this element in different meteorites. Only one type of meteorites exhibited a composition similar to that of Earth: CI chondrites. “If the process had been more random, we would not have identified a single type of meteorite, but a mixture”assure Martin Schiller.
Other meteorites, from Mars, for example, show that the isotopic composition of iron was different in the materials that were used at the very beginning of the growth of our Planet. Probably because of the temperatures then prevailing in the vicinity of our young SoleilSoleil. After a few hundred thousand years, our Solar System cooled enough for CI chondrite dust from outside to enter the proto-Earth accretion region.
“This dust dominates the composition of the Earth’s mantle. This is only possible if the majority of the older iron had already migrated to the core. And so, if the formation of this nucleus – what researchers call planetary differentiation – took place very quickly”, explains Martin Schiller. “This discovery not only clarifies the history of our Solar System, but it could also shed light on how planets form elsewhere in the world. galaxygalaxy. »
“Water could be a simple co-product of planet formation”
“If our theory holds true, water may well turn out to be a simple co-product of planetary formation. » Enough to make one of the main ingredients of life – as we know it – extremely commonplace in our Universe.
Formation of the Earth: one of the geochronometers was wrong
The Earth and the Solar System were born approximately 4.568 billion years ago. For the events that followed there is now a doubt since a new evaluation, revised downwards, of the half-lifehalf-life of a radioactive isotope of samariumsamarium, one of the geochronometers used to date what happened there during the first hundreds of millions of years of their evolution. There differentiationdifferentiation planet Earth, the LuneLune and Mars, would have happened faster and earlier than we thought.
Article of Laurent SaccoLaurent Sacco published on 09/04/2012
This is not a questioning of the age of the Earth and the Solar System. But an article published in Science proves the need to rethink the timeline of events during the Hadean on Earth, Mars, and the Moon. If you ask Wolfram Alpha to tell you all about the isotope of samarium 146, it will teach you that it is radioactive and with a half-life long enough to allow the dating of ancient geological processes unlike carbon 14 and its half-life of only 5,730 years. But it is above all, in indirect relation with today’s measurable abundances of the isotopes of neodymiumneodymium that it makes it possible to date processes having occurred atdawndawn of the history of the solar system.
But there it is, the figure of 103 million years given for 146Sm is wrong! According to a group of researchers who used theArgonne Tandem Linac Accelerator System from the Argonne National Laboratory in the United States, the true half-life value of samarium-146 is 68 million years.
No revolution for the age of the Solar System but, on the other hand, as regards the established chronology of the events that occurred during the first hundreds of millions of years inside the rocky planets, we will have to review the copy!
Thanks to samples of lunar rocks and Martian meteorites, as well as terrestrial rocks, we had estimated the dates of differentiation of these planets, that is to say the formation of chemically well-separated cores and coats. By taking into account the new value of the half-life of samarium, these differentiations would have occurred more quickly and the ages estimated with other nuclear clocks become convergent according to the researchers.
Faster formation of the Moon’s mantle
Among the oldest rocks in the world, some are showing signs of age as well as the geodynamic and geochemical processes they witness. Already, we can draw up a first assessment, which is as follows.
Terre
- A mantle process that formed some rocks in Greenland was believed to have occurred 170 million years after the formation of the Solar System. The revised age of 120 million years is now more in line with that determined by another nuclear clock related to rocks found in Australia. This suggests that this process has affected the entire Planet.
- Similarly for rocks in Canada, we go from 287 to 205 million years after the formation of the Solar System for another process.
Lune
- The formation of the lunar mantle has been dated to 242 million years after the formation of the Solar System. The revised age is now 170 million years.
- A lunar rock was recently dated with three stopwatchesstopwatches nuclei, one of them being samarium 146. The ages taken from the other two clocks agreed, while the age estimated from samarium 146 differed. The revised version of the half-life of samarium 146 solved the riddle.
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