A new study led by geophysicist Steve Jacobsen of Northwestern University and seismologist Brandon Schmandt from the University of New Mexico has yielded evidence that vast oceans worth of water are tied up within Earth’s mantle. The results are published in Science.
Four hundred miles beneath North America, Schmandt and Jacobsen found deep pockets of magma, which indicates the presence of water. However, this isn’t water in any of the three forms we are familiar with. The pressure coupled with the high temperatures forces the water to split into a hydroxyl radical (OH) which is then able to combine with the minerals on a molecular level.
This water, which is bound up in rock, could indicate the largest water reservoir on the planet. It is believed that plate tectonics cycle the water in and out, and the water affects the partial melting of rock in the mantle.
"Geological processes on the Earth's surface, such as earthquakes or erupting volcanoes, are an expression of what is going on inside the Earth, out of our sight," said Jacobsen in a press release. "I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades.”
(...) For this study, the researchers utilized the USArray, which collects information from over 2,000 seismometers in the United States. The observations were supported by computer models that replicated conditions from the transition zone. The key to storing the water, they found, is a mineral called ringwoodite, which is a form of olivine that exists under high pressure and temperature.
"The ringwoodite is like a sponge, soaking up water," Jacobsen said. "There is something very special about the crystal structure of ringwoodite that allows it to attract hydrogen and trap water. This mineral can contain a lot of water under conditions of the deep mantle.”