(ORDO NEWS) — After analyzing the composition of mineral sand grains, scientists have found a connection between the movement of the solar system in the galaxy and the rhythm of the formation of the continental crust of the young Earth.
Unstable gravitational conditions in the spiral arms of the Milky Way provoked meteor bombardments of our planet by Oort cloud objects.
The authors of the new study suggest that thanks to those meteorites, “grains” of the first continents formed on the young Earth and tectonic processes started.
Today, the Earth’s crust is broken up into plates that move slowly across the more plastic asthenosphere, the layer of the upper mantle. The continental crust is more “floating” and less dense than the oceanic.
Therefore, where they “meet”, the oceanic crust goes deeper into the Earth, melting into the mantle. Because of this activity, pieces of the mantle regularly “float” to the surface and splash out with volcanic eruptions, forming a new continental crust. So there was an assumption that the first continents were formed above the subduction zones.
Unfortunately, everything turned out to be much more complicated, because in the Catarchean (up to four billion years ago) and Archean (2.5-4 billion years ago), there was probably no tectonic movement of plates and subduction zones.
To reconstruct the early history of crustal formation, some geologists have switched from studying large-scale plate movements to studying the minute mineral crystals that formed on the young Earth.
It is a mistake to assume that the crust was formed exclusively due to terrestrial processes. Throughout its existence, the planet has been influenced by the cosmic environment: from periodic changes in the orbit and cycles of solar activity to distant gamma-ray bursts and, of course, meteorite impacts.
In early August , a study was published that showed that meteorite impacts on the young Earth split the planet’s shell and provoked the formation of floating “grains” of the continental crust.
Now, another international team of scientists has discovered a “rhythm” in the formation of the continental crust that coincides with the movement of the planet through the Galaxy. In both works, geologists analyzed zircons.
Zircons are mineral grains formed when magma cools. Sometimes, in this process, other elements like uranium get into them, which, due to radioactive decay, allow us to determine the age of the grain.
After analyzing grains from different cratons (areas of the crust characterized by low mobility), scientists have identified a repeating rhythm of their formation lasting about 200 million years, coinciding with the rotation of the solar system around the center of the Galaxy and the passage of spiral arms.
In spiral arms, the concentration of stars, interstellar dust and gas is much higher. There are regions of star formation. Their gravitational interactions knock the objects of the Oort cloud out of their orbits, and they begin to collide with the planets more often.
Most of the objects falling to Earth come from the Asteroid Belt, they arrive at a speed of about 15 kilometers per second. Objects from the Oort cloud – at a speed of about 52 kilometers per second. Crashing into the planet, they knocked out a huge amount of crust, provoking the “emergence” of the molten mantle.
Over time, the average size of falling meteorites and impacts became less destructive. At the same time, subduction processes started on the planet, and it itself began to “produce” continents.
So the passages of the solar system through the spiral arms provoked meteorite bombardments of the young Earth, as a result of which the first continental crust was formed, scientists suggest.
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