Where is there more water?

2002/03/11 Carton Virto, Eider - Elhuyar Zientzia

• Geologia

Researchers at the Tokyo Institute of Technology have studied the bottom of the mantle, a layer at 650 and 2,900 kilometers deep, and have announced that 0.2% of its components in weight can be water. Do not think that after making a hole there, we will solve the problem of water scarcity, but according to geologists, water can give us clues about the process of formation of our planet and plate tectonics.

The formation of the planets is analyzed taking into account the amount of volatile material existing in the first moments, among which are carbon dioxide and water. From the calculations of the Japanese researchers it follows that the original mixture of the Earth was not as strong as expected.

On the other hand, the presence of water in the lower mantle also affects plate tectonics. As water reduces the melting point of the rocks of the lower mantle and increases the viscosity of the medium, the mantle with abundant water will move and mix faster. This movement conducts the plates and mixes the materials, so the water of the lower mantle conditions the movement of tectonic plates. According to the researchers, water accelerates and facilitates the sinking of the plates.

Small scale mantle in laboratory

To carry out the research, the low mantle has been reproduced in the laboratory. The three main components of the region (two rich in magnesium and calcium and a mixture of magnesium and iron oxide) at 1,600 °C and 2,5000 atm. The hydrogen content is put under pressure of and measured. It is considered that hydrogen from rocks comes from captured water, so it is considered an indicator of water. From the experiment carried out by the Japanese it follows that in the lower mantle there is much more water than expected.

The debate, of course, will be intense among geologists, since two years ago a similar investigation was conducted and it was concluded that in the low mantle there was hardly any water. Between the high mantle and the low mantle, between 400 and 650 km, it was known that there is as much water as the volume of several oceans, but it was thought that it was not under. But "although the minerals of the lower mantle have the capacity to contain ten times less water than those of above, the volume is much higher and there can be a lot of water," explain the Japanese.

More information: Web page of the journal Nature