Scientists disagree about the appearance of water on Earth. So, until recently, the hypothesis was quite popular that initially the water reserves on the planet were of cosmic origin. Recently, our compatriot, Skoltech professor Artyom Oganov, together with his colleagues from Nankai University (China) - Professor Xiao Dong and his team, expressed a new hypothesis: water came from below, from underground.
As you know, a significant part of our planet is occupied by oceans. For their formation, simply gigantic volumes of water were required. And what, she all fell from the sky?
“It was hypothesised that comets could bring water to us, but, apparently, the significance of this source is very small,” says Professor Oganov. “The fact is that the isotopic composition of water on Earth and in comets differs markedly.”
Consequently, the main source of water could only be the bowels of the earth. But here, too, everything is not so simple. The fact is that for the first tens of millions of years of the planet's existence, its surface was hot, and also bombarded by asteroids and other cosmic bodies.
The researchers calculated that as a result of these cataclysms, the upper layers of the lithosphere should have melted to a depth of at least several hundred kilometres. And the water from the surface should have completely evaporated.
Experts came to the conclusion that in this case there must have been some substance capable of retaining water in the bowels for millions of years, and then releasing it outside.
Oganov succeeded in inventing the USPEX crystal structure prediction method, which made it possible to find out the composition of the desired substance. It turned out to be magnesium hydrosilicate Mg2SiO5H2. Now there is no such substance on Earth, but it could have been present here earlier, predetermining the evolution of the planet.
According to experts, this compound contains 11 per cent of water by weight of the substance. In addition, it does not break up even at very high temperatures and pressures of more than 2 million atmospheres (similar to the pressure in the earth's core). Scientists believe that for the first 30 million years of the planet's existence, some of the water was "stored" at the core level in the form of hydrosilicates. The core then had a different composition: in particular, it lacked iron.
However, with the concentration of iron in the centre of the Earth and the formation of the core, hydrosilicates were gradually forced out of the central region of the planet into a zone of lower pressure. There their stability was broken, and they began to disintegrate. This led to the formation of magnesium oxide and silicate, which make up the earth's mantle today, as well as H2O, that is, water.
Another 100 million years took the rise of life-giving moisture to the surface of the planet. And then, as we already know, oceans began to form, where the first living organisms arose.