Environment Counts | Evidence for vast quantities of water deep in Earthâ€™s mantle :
It has been suggested that the Earthâ€™s transition zone, at depths between 410 and 660â€‰kilometres, could be a major repository for water. A transition zone containing significant quantities of water may have a key role in plate tectonics. The types of rocks in this zone which include ringwoodite, have been shown to be able to store significant quantities of water, estimated at up to 2.5 % of their weight. Despite experimental demonstration of the water-bearing capacity of these types of rocks, the issue of whether the transition zone contains abundant water remains highly controversial.
This article reports X-ray diffraction, Raman and infrared spectroscopic data that provide the first evidence for the terrestrial occurrence of ringwoodite containing water. This was found in a diamond from JuÃna, Brazil. The water-rich nature of this inclusion, indicated by infrared absorption, along with the preservation of the ringwoodite, is direct evidence that the transition zone contains significant water estimated at about 1 % by weight. The transition zone could hold as much water as all the Earthâ€™s oceans put together. Nature 507, 221â€“224 (13 March 2014) doi:10.1038/nature13080