Northwestern University researchers, along with colleagues from the University of New Mexico, found evidence of vast storehouses of a type of blue rock called ringwoodite, which is a “high-pressure polymorph of olivine (a magnesium iron silicate) that is formed at high temperatures and pressures” deep in Earth’s mantle.
Geologists have long wondered how much water is transferred between the oceans of the earth and reservoirs beneath the crust. This material can be carried hundreds of miles through the ground by tectonic forces, driven by continental drift.
Water driven into the mantle can help drive melting of rock, forming polls of magma.
Research on this topic will undoubtedly continue in the future.
This finding is very important, because approximately 1 1/2% of the ringwoodite is composed of water, and it is believed that the water contained in this material is greater than all of the earth’s oceans combined.
Some geologists think water arrived in comets as they struck the planet, but the new discovery supports an alternative idea that the oceans gradually oozed out of the interior of the early earth. The hidden water could also act as a buffer for the oceans on the surface, explaining why they have stayed the same size for millions of years.
Steven Jacobsen’s team, of Northwestern University in Evanston, Illinois used 2000 seismometers to study the seismic waves generated by more than 500 earthquakes. These waves move throughout the water layer revealed itself because the waves slowed down, as it takes them longer to get through soggy rock than dry rock.
A sample of ringwoodite was found in a diamond that was expelled from a volcano in 2008. The diamond came from the “transition zone” between the upper and lower mantle.
“We should be grateful this deep reservoir,” says Jacobsen. “If it wasn’t there, it would be on the surface of the Earth, and mountain tops would be the only land poking out.”