For a long time, textbooks They have painted the primitive Earth like a ball of infernal and static magma, being a “lid” of inert rock where life or complex geological movement was impossible. Specifically, it was thought that the plate tectonicsthe engine that shapes the continents and recycles our planet’s nutrients, had taken much longer to start. However, we were wrong.
How he did it. Science, in a recent article, has just put on the table the definitive evidence that indicates that the Earth began to move much earlier than we believed: at least 3.3 billion years ago, and most likely, more than 4 billion ago. And the key is not in the gigantic mountains under our feet, but in small fragments of glass smaller than a grain of sand.
And if we want to travel in geological time, you have to go to jack hillsin Western Australia, where the oldest known fragments of terrestrial rock are found. The protagonists of this story are zircon crystals, extremely resistant minerals that act as authentic geological hard drives. The interesting thing is that, when they form, they trap isotopes and tiny amounts of other elements inside that tell us exactly what the environment was like at the time of their crystallization.
The results. According to detailed analysis that collects Natureand supported by key works such as those published in the prestigious magazine PNASthese S-type zircons hide unmistakable geochemical signatures. Specifically, they reveal that, instead of a static and dead Earth’s crust, subduction processes already existed. That is, the oceanic crust was already colliding and sinking under other plates, melting back into the Earth’s mantle.
A double life. But researchers have not limited themselves to looking at a specific era, but have traced the proportions of trace elements such as uranium, niobium or scandium in different zircons from Australia, Greenland and South Africa. Here they observed that during the Eoarchean, the Earth did not have a single geological behavior.
Instead, it had two tectonic regimes. The first of these, known as a ‘stagnant lid’ with areas of crust dominated by plumes of oceanic magma that simply pushed upwards. On the other hand, it also had the ‘moving lid’ zone, which were active zones where volcanic arcs were already forming and there was subduction, very similar to modern plate tectonics, recycling the Earth’s crust.
But there is more. As if that were not enough, other published studies in Science and Geology have contributed even more pieces to the puzzle, such as the transform faults in the Pilbara Craton of Australia that show horizontal movements 3,000 million years ago, and even inclusions of fresh water in zircons from more than 4,000 million years ago, which suggests that there were already emerging continents interacting with the atmosphere and the water cycle.
It changes everything. Knowing that plate tectonics started so early is not a mere geological whim, since tectonics is the Earth’s thermostat: it regulates the carbon cycle, releases fundamental gases into the atmosphere and creates the necessary environments for the chemical breeding ground.
In this way, if more than 4,000 million years ago our planet was already recycling its crust, having primitive continents and fresh water, it means that the conditions for life to emerge occurred much earlier than what science books dictated. Once again, the Earth shows us that, from its most remote beginnings, it has always been a living world.
Images | Javier Miranda
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