(ORDO NEWS) — The chemical composition of zircon crystals found in South Africa has provided scientists with the earliest evidence of plate movement. Probably, about 3.8 billion years ago, the surface of our planet ceased to be a stable stone shell and tectonic processes began in it.
The earth’s crust and the upper layer of the mantle below it are divided into lithospheric plates. Core heat sets the viscous layers of the mantle beneath the plates in motion, causing tectonic activity responsible for volcanic eruptions, earthquakes and uplifting of mountain ranges.
There was no consensus among scientists when exactly the modern Earth’s crust formed: estimates ranged from four billion to 800 million years ago.
Such a spread is associated with the lack of geological data on the young Earth due to the constant circulation of substances in the surface of the plates themselves. Now there are practically no rocks left on the planet dating from the first 500 million years of its existence.
Now a team of American scientists was able to more accurately determine the time of the beginning of tectonic activity on Earth. Researchers have discovered 33 crystals of the silicate mineral zircon in South Africa: the layer in which they were found formed 3.3-4.15 billion years ago.
The zircon crystals, described in an article for the AGU Advances magazine, contained the oldest evidence of subduction – the submergence of one lithospheric plate under another.
Hafnium isotopes and the composition of trace elements in zircons made it possible to determine the conditions for the formation of zircon.
The crystals, less than 3.8 billion years old, formed in rocks experiencing pressures and temperatures similar to those found in today’s subduction zones. At the same time, older zircons were formed as a result of the melting of mantle rocks, which remained stable for 600 million years.
Thus, about 3.8 billion years ago, the surface of the Earth ceased to be stable and the first tectonic processes began in it. Scientists suggest that this transition was gradual. Probably, the changes began and ended in various places on the planet before becoming a global tectonic movement, which we observe to this day.
Plate tectonics shapes the Earth’s atmosphere through the release of volcanic gases. In addition, it creates silicate rocks that capture carbon dioxide from the atmosphere, thereby moderating temperature fluctuations.
Among all the studied planets, tectonic activity was revealed only on Earth – perhaps it was she who played a decisive role in creating conditions suitable for the emergence of life.
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