Scientists at Harvard University in the United States have proved that the Earth in the past, before the emergence of life, was an almost completely ocean-covered planet, but over time, huge volumes of water were absorbed by the mantle. This was reported in an article published in the AGU Advances magazine.
Most of the water deep underground is believed to exist in the form of hydroxyl compounds, made up of oxygen and hydrogen atoms. Specifically, water is stored in two types of high-pressure volcanic mineral olivine: wadsleyite and ringwoodite.
Scientists have collected all available mineral physics data and quantified the water holding capacity of wadsleyite and ringwoodite over a wide range of temperatures. Scientists have found that the higher the temperature, the less water is able to hold minerals. Since the interior of the early Earth was hotter, the mantle absorbed less water, but as it cooled, it became more capacious. Currently, it is capable of storing water in an amount exceeding the mass of the World Ocean by 1.86-4.41 times.
This is consistent with the data obtained from the analysis of oxygen isotopes, according to which there was much less land on Earth 3.2 billion years ago than today, and the planet was a kind of water world.