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 other planets in our solar system. But by simulating the possible origins of the atmosphere of Venus, our closest neighbour, a team of scientists suggests that the planet could have witnessed 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. For example, Alfred Wegener, known for his theory of continental drift, identified at the beginning of the twentieth centuryH Century of common fossils in South America and West Africa; By showing that the shapes of the two continents could fit together, he assumed that they had been 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, which appears to be specific to our planet
Thus, according to this model, the Earth’s lithosphere (the solid crust of our planet at the surface, composed of the crust and part of the upper mantle) is divided into several distinct plates, which move relative to each other. By “sliding” on the asthenosphere (the elastic part of the upper mantle, able to deform without breaking). Today there are fifteen major tectonic plates, whose movements create geologically active areas at their boundaries, for example when two plates converge, diverge or slide relative to each other. These movements are the origin of many geological phenomena, such as volcanoes, earthquakes, and the formation of mountain ranges or ocean trenches.
All these tectonic movements allow chemical exchange between the Earth’s interior and its surface, and mean regular renewal of its surface rocks. According to the most plausible hypotheses, our planet would not always have experienced such active tectonic activity, but instead would have shown very limited tectonic activity in its early moments. The emergence of life on Earth was probably closely linked to the change from this tectonic regime to the current one. This change would have stabilized the global temperature on the surface of our planet and created a suitable environment for the emergence of life.
Do we know about other planets that show tectonic activity?
While we don’t know of any other planets in our solar system that exhibit tectonic activity similar to Earth’s, some scientists believe this was not always the case. This is for example the case of Venus, our closest neighbour: despite many notable differences with our own 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 its mass, size, or even density. According to the most plausible models, today’s Venus has only a single stagnant plate, severely limiting exchanges between its interior and exterior.
But according to a team of scientists from Brown University in the United States, the current atmosphere of Venus does not appear to be consistent with this unique plate tectonic model. By simulating the possible origins of Venus’ atmosphere (90 times denser than Earth’s, and composed mainly of carbon dioxide and nitrogen), the researchers suggest that Venus would not have experienced such limited tectonic activity throughout its history. In fact, high levels of nitrogen and carbon dioxide in Venus’ atmosphere would only be possible if Venus had experienced tectonic activity in the past similar to early Earth’s tectonic activity, i.e. consisting of just a few plates moving relative to each other. The researchers present their findings in the journal nature. According to them, this tectonic activity would have allowed massive degassing of volcanic gases, resulting in the current atmosphere of Venus.
Models of planetary evolution are being called into question
According to their hypothesis, Venus could have formed tectonic plates about 1 billion years ago, i.e. -4.5 to -3.5 billion years ago. The phenomena that led to the disappearance of the conditions that allow the movement of tectonic plates, resulting in extreme temperatures and a thick atmosphere of Venus, are not known. According to this new guess at the geological history of Venus, Venus and Earth actually had a very similar early history, with both planets exhibiting tectonic activity during their early days. However, Earth’s tectonic activity grew to give rise to many tectonic plates, while Venus’ tectonic activity gradually decreased to its current pattern of a single stagnant plate. According to scientists, the early tectonic activity of Venus may have been favorable for the emergence of life as we know it, but such conditions no longer exist there.
This new theory calls into question what we know about the evolution of terrestrial planets: according to previous hypotheses, the presence of tectonic plates on a given planet was a binary problem: either the planet presents tectonic activity, or it does not present any. Evidence of past tectonic activity on Venus suggests that the planet may have transitioned from one phase of tectonic activity to another. Thus, if the emergence of life is linked to tectonic activity, some planets may intermittently provide conditions favorable to life, rather than being continuously habitable. According to these hypotheses, the Earth’s ongoing tectonic activity would actually be an exception.