Earth’s mantle contains ringwoodite, a type of saturated rock that holds within it a huge ocean of water in its molecular form, according to a recent study coauthored by geophysicist Steve Jacobsen of Northwestern University. Jacobsen has stated that he believes this might be evidence that Earth’s water came from underground reserves of it, in its molecular form, through melting of rocks. Jacobsen and other scientists from Northwestern University and the University of New Mexico conducted the research.
Water can exist in four different forms, liquid, solid (ice), gas, and molecular. An enormous reservoir of water, possibly trapped in its molecular form in a layer of ringwoodite in the Earth’s mantle, may be where much — or all — of Earth’s water came from.
Ringwoodite is a type of rock that has a crystalline structure, This structure is thought to act somewhat like a sponge. It attracts and traps the two atoms that, together, make water — oxygen and hydrogen.
While a layer of ringwoodite in the Earth’s mantle has not been verified — yet — there are signs that indicate a layer of this material containing a vast ocean of water in its molecular form is contained within the mantle of our planet.
One piece of evidence that suggests the presence of this layer of ringwoodite is a diamond that was discovered earlier in 2014 that was brought up to Earth’s surface by the eruption of a volcano. The diamond, when closely examined, was found to contain a little bit of ringwoodite inside of it, and the ringwoodite contained a surprising amount of water in its molecular form, according to Nature.
Finding the diamond, in and of itself, might not seem like a lot of evidence, but scientists discovered further evidence when they tracked the vibrations, or seismic waves, produced by earthquakes all around the world. They used seismic data from the USArray, a network of 2,000 seisometers, and found that the seismic waves seemed to be traveling –not through dry rock, but through saturated rock. The scientists used the information that came from analyzing the seismographs to determine how large the reservoir of water could potentially be.
The water both on the surface of our planet and contained within it in molecular form, according to the researchers, might be undergoing a cycle due to the action of plate tectonics. Steve Jacobsen and the other scientists, like University of New Mexico seismologist Brandon Schmandt, point to yet another potential piece of evidence. About 400 miles beneath the surface of North America are large pockets of magma. The presence of the magma pockets, according to the scientists, is a signature that water, also, is located at these depths. The water could have been released from its molecular state into a liquid state due to the saturated layer of rocks being partially melted through the action of plate tectonics. This partial melting of rocks is referred to as dehydration melting.
According to Jacobsen, the evidence that they’re analyzing may be proof “for a whole-Earth water cycle.” He added that “Scientists have been looking for this missing deep water for decades.” While most of the water might be in its molecular form at anywhere from 250-410 miles deep within Earth’s mantle, it could be transformed by the heat generated through plate tectonics into its liquid form.
The layer of saturated rock, possibly made up of ringwoodite, is in a part of the Earth’s mantle known as the transition zone. If water in its molecular form makes up just one percent of the weight of the rock in this zone of the mantle, according to the researchers that would amount to almost three times the quantity of water in all of the planet’s oceans.
Over the course of several years, Jacobsen has been creating synthesized sapphire-blue colored ringwood in his lab at Northwestern University. He has done this by subjecting green olivine — which the Earth’s upper crust is rich in — with water, under the type of high pressures that would be associated with conditions within the transition layer of Earth’s mantle. His finding was that the ringwoodite he produced was able to contain one percent of its overall weight in water in its molecular form, just as was found within the ringwoodite in the diamond.
Though the scientists who researched and analyzed the data from the seisometers have determined that the saturated layer of rock contains possibly a huge ocean of water in its molecular form, more research needs to be done to find out if the layer exists all round the planet within Earth’s mantle.
Dr. Jacobsen has stated that the Earth’s water likely came from the interior of the earth, within our planet’s mantle contained in its molecular state, rather than some other source, like comets. There could be up to three times more than the amount of water contained in all of the planet’s oceans contained in this layer of saturated rock in the transition zone of Earth’s mantle. The findings of the study, titled Dehydration melting at the top of the lower mantle, were published in the June 13 issue of Science journal. Some of the funding for the research came from the David and Lucile Packard Foundation and the National Science Foundation.
Written by: Douglas Cobb