Geologists Have Estimated The Share Of The Earth's Primary Crust In The Modern Mantle Of The Planet
In the samples of mantle rocks from the mid-ocean ridges, there were unexpectedly many fragments of matter that made up the primary crust of the Earth. This suggests that the cycle of rocks in The Earth's crust began from the first moments of the planet's existence. The research was published in the scientific journal Science Advances.
"We have shown that some fragments of the ancient oceanic crust go back to their "homeland," in the vicinity of the mid-ocean ridges. It moves through the mantle like a salmon returning to its spawning ground. We found out that this is a closed cycle that very unevenly distributes ancient matter along these seamounts," said one of the authors of the work, Professor Munir Humayun of the University of Florida (USA).
The Earth's interior consists of several layers – a solid crust, a semi-liquid mantle, and molten metalcore. The crust is divided into several huge fragments – tectonic plates that slowly "float" on the surface of the mantle and collide with each other. Because of these collisions, continents, mountain ranges, and other major terrain irregularities appear and disappear.
In recent years, scientists have begun to actively argue about when these plates began to move and when the first continents appeared on Earth. In recent years, geologists have found a lot of theoretical and practical evidence in favor of the fact that this could have happened almost immediately after the formation of the planet, and about 3.2 billion years ago.
The eternal cycle of the Earth's rocks
In the new study, Humayun and his colleagues studied about 500 samples of upper mantle rock from three dozen different locations on the floor of the Atlantic and Pacific oceans, in the vicinity of the so-called mid-ocean ridges. As a result, scientists have found new evidence that the cycle of rocks in The Earth's crust began almost immediately after the formation of the planet.
Samples were collected from faults between tectonic plates, through which mantle rocks gradually rise to the Earth's surface, form a new oceanic crust, and "push" old deposits toward continents. There, this part of the oceanic crust sinks and begins its movement deep into the bowels of the planet.
Geologists have long debated what exactly is happening to the rocks of the former crust at this moment. Some scientists believe that as they move deeper into the mantle, they completely dissolve, while others suggest that a significant part of the rocks of the former crust survives this journey and returns to the surface.
The authors of the article tried to find an answer to this question. They drew attention to the fact that the rocks of the new marine crust that were formed by these two routes must have different ratios of scandium and germanium, as well as different proportions of iron and manganese and niobium and thallium. Based on these considerations, Humayun and his team analyzed the concentration of these elements in the resulting samples and compared them with what both theories predict.
As it turned out, among the 500 samples were rocks with both sets of elements, which suggests that some of the matter of the ancient crust is preserved during the movement of rocks through the mantle. According to geologists ' calculations, it accounts for 5 to 6% of the total mass of rocks in the upper mantle layers.
Such a large number of ancient rocks was a surprise for geologists since it simply would not have had time to accumulate in the mantle if tectonic processes started about 3 billion years ago.
Therefore, this suggests that the cycle of rocks in The Earth's crust began almost from the moment of its origin. At the same time, it has always flowed at about the same speed as today. This idea completely contradicts modern ideas about plate tectonics, so scientists will have to confirm them again with other discoveries, Humayun and his team conclude.