A new study suggests the Earth may have made its own water deep within its crust, as well as receiving the vital substance from extraterrestrial objects such as icy comets.
A team of researchers revealed evidence of an unknown geochemical pathway used by the Earth to sequester water deep within, releasing small amounts through plate tectonics in a process that feeds our oceans "from within," Ohio State University reported.
Past theories about the Earth's early days suggest it was dry and inhospitable to life until it was pummeled by icy comets, which deposited water onto the surface; these new findings provide an alternative idea.
"When we look into the origins of water on Earth, what we're really asking is, why are we so different than all the other planets?" said Wendy Panero, associate professor of earth sciences at Ohio State. "In this solar system, Earth is unique because we have liquid water on the surface. We're also the only planet with active plate tectonics. Maybe this water in the mantle is key to plate tectonics, and that's part of what makes Earth habitable."
Some rocks may appear dry to the human eye, but can actually can contain hydrogen atoms that bond with oxygen and create water when released. While these atoms make up only a small fraction of mantle rock, but since this type of rock makes up about 80 percent of the Earth's volume this can still add up to a significant amount of water.
To make their findings the researchers compressed various minerals that are common to the mantle and put them under high pressures and temperatures using a diamond anvil cell, which squeezes material between two diamond and hits them with a laser. This technique allowed researchers to simulate he conditions of the deep Earth. The researchers looked at how the minerals' structures changed under these conditions to determine whether or not they would be able to store hydrogen and used computer calculations to find out how these atoms could potentially escape.
The researchers found the mineral ringwoodite contains enough hydrogen to make it a potential candidate for deep-Earth storage. Ringwoodite is found up to 500 miles below the Earth's surface in a region called the "transition zone," which is believed to be able to hold a "world's worth" of water. From this region, the same convection of mantle rock that leads to plate tectonics could bring the water to the surface.
If these findings are true, the Earth could hold half as much water as is in its oceans deep within.
"If all of the Earth's water is on the surface, that gives us one interpretation of the water cycle, where we can think of water cycling from oceans into the atmosphere and into the groundwater over millions of years," Panero said. "But if mantle circulation is also part of the water cycle, the total cycle time for our planet's water has to be billions of years."
The findings were presented at the American Geophysical Union (AGU) meeting on Dec. 17.