THE transition zone between the Earth’s upper and lower mantle contains considerable quantities of water, according to an international study. The research team analysed a rare diamond formed 660 meters below the Earth’s surface using techniques including Raman spectroscopy and FTIR spectrometry. The study confirmed something that for a long time was onlyatheory,namelythatocean wateraccompaniessubducting slabs and thus enters the transitionzone.Thismeansthatour planet’swatercycleincludesthe Earth’s interior.

 

“These mineral transformations greatly hinder the movements of rock in the mantle,” explains Prof. Frank Brenker from the Institute for Geosciences at Goethe University in Frankfurt. For example, mantle plumes --rising columns of hot rock from the deep mantle -- sometimes stop directly below the transition zone. The movement of mass in the opposite direction alsocomestostandstill.Brenker says, “Subducting plates often have difficulty in breaking through the entire transition zone.

 

So there isawhole graveyard of such plates in this zone underneathEurope.”However, untilnowitwasnotknownwhat the long-term effects of “sucking”materialintothetransition zone were on its geochemical composition andwhetherlarger quantities of water existedthere. Brenker explains: “Thesubducting slabs also carrydeep-seasedimentspiggy-backinto the Earth’s interior. These sediments can holdlarge quantities of water andCO2.Butuntilnowitwasunclearjust how much enters the transition zone in the form of morestable, hydrous minerals andcarbonates -- and it was therefore also unclear whether largequantities of water really arestored there.”