2023-11-02 20:20:05
The movement of tectonic plates on the surface of our Planet seems to be a very rare phenomenon, because it is not observed on any of the other planets in our Solar System. But by simulating the possible origins of the atmosphere of Venus, our closest neighbor, a team of scientists suggests that the planet could have experienced plate tectonics in the past.
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The model of plate tectonics was born from the observation of strong similarities between different continents on the Earth’s surface. Alfred Wegener, known for his theory of continental drift, had for example identified at the beginning of the 20th century fossils common to South America and western Africa; by further showing that the shapes of the two continents could fit together, he hypothesized that they were stuck together in the past. Over time, arguments for the theory of plate tectonics grew, and the model was finally accepted in the 1960s.
A complex model, apparently specific to our Planet
Thus, according to this model, the terrestrial lithosphere (the rigid shell of our Planet located on the surface, made up of the crust and part of the upper mantle) is divided into several distinct plates, which are in motion relative to each other. by “sliding” on the asthenosphere (the ductile part of the upper mantle, capable of deforming without breaking). Today there are fifteen major tectonic plates, the movements of which create geologically active zones at their borders, for example when two plates converge, diverge or slide relative to each other. These movements are at the origin of numerous geological phenomena, such as volcanism, earthquakes, the formation of mountain ranges or ocean trenches.
All of these tectonic movements thus allow a chemical exchange between the interior of the Earth and its surface, and imply a regular renewal of its surface rocks. According to the most commonly accepted hypotheses, our Planet did not always experience such active tectonics, but instead would have exhibited much more limited tectonic activity in its earliest moments. The appearance of life on Earth would have been closely linked to the change from this tectonic regime to the current regime. This change would have triggered a stabilization of the global temperature on the surface of our Planet and the establishment of an environment favorable to the appearance of life.
Do we know of other planets exhibiting tectonic activity?
While we do not know of any other planets in our Solar System exhibiting tectonic activity similar to that of Earth, some scientists believe that this has not always been the case. This is for example the case of Venus, our closest neighbor: despite many notable differences with our Planet (on Venus, the surface temperature is high enough to melt lead, and the pressure there is 90 times higher than on Earth), the two neighbors have strong similarities, such as their mass, their size, or even their density. According to the most commonly accepted models, Venus today only has a single, stagnant plate, strongly limiting exchanges between its interior and the outside.
But according to a team of scientists from Brown University in the United States, the current atmosphere of Venus does not appear consistent with this unique tectonic plate model. By simulating the possible origins of Venus’ atmosphere (90 times denser than on Earth, and consisting mainly of carbon dioxide and nitrogen), the researchers suggest that Venus would not have experienced such limited tectonic activity throughout the throughout its history. The high levels of nitrogen and carbon dioxide in the Venusian atmosphere would in fact only be possible if Venus had experienced in the past tectonic activity similar to the early tectonic activity of the Earth, i.e. composed of a few plates moving relative to each other. Researchers present their results in the journal Nature. According to them, this tectonic activity would have allowed significant volcanic degassing, resulting in the current Venusian atmosphere.
Models of planetary evolution called into question
According to their hypothesis, Venus would have presented tectonic plates for around a billion years, between -4.5 and -3.5 billion years ago. The phenomena that led to the disappearance of the conditions allowing the movements of the tectonic plates, resulting in the extreme temperatures and the thick atmosphere of Venus, are not known. According to this new conjecture of the geological history of Venus, the latter and the Earth would in fact have had very similar early histories, with both planets exhibiting tectonic activity during their early days. However, Earth’s tectonic activity grew to lead to the appearance of numerous tectonic plates, while Venus’ tectonic activity gradually declined to lead to its current pattern of a single stagnant lid. According to scientists, the early tectonic activity of Venus could have been favorable to the appearance of life as we know it – these conditions are no longer present there today.
This new theory calls into question what we know about the evolution of terrestrial planets: according to previous hypotheses, the existence of plate tectonics on a given planet was a binary problem: either the planet presents tectonic activity , or it does not present any. The evidence of past tectonic activity on Venus indicates the possibility for a planet of a transition from one phase of tectonic activity to another. Thus, if the appearance of life is linked to tectonic activity, certain planets could intermittently present conditions favorable to life, instead of being continuously habitable. According to these hypotheses, the continuous tectonic activity of the Earth would in fact be an exception.
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