WOW! That’s interesting! While some scientists think Earth’s oceans formed when icy comets hit the planet, a recent research suggests oceans simply seeped out of the center of the Earth.
The finding, published in Science, suggests that a reservoir of water is hidden in the Earth’s mantle, more than 400 miles below the surface. Try to refrain from imagining expanses of underground seas: all this water, three times the volume of water on the surface, is trapped inside rocks.
Called ringwoodite, the rock is bright blue and is only formed at high temperature and pressure in the Earth’s mantle. The water would have been squeezed out of the rocks, “almost as if they’re sweating,” explained Steven Jacobsen of Northwestern University.
This research adds to our understanding of the complexities of the water’s transport throughout the sky, across the oceans, and into the ground. From the Editor’s Summary of the study in Science:
“The water cycle involves more than just the water that circulates between the atmosphere, oceans, and surface waters. It extends deep into the Earth’s interior as the oceanic crust subducts, or slides, under adjoining plates of crust and sinks into the mantle, carrying water with it.”
The team of scientists used seismometers to measure the motion of energy waves caused by earthquakes through the ground below the United States. The waves slowed down as they passed through the region of the mantle containing ringwoodite. The scientists suggest that the saturation of ringwoodite with water explains the sluggishness of the waves through this particular region of Earth’s center.
Is water the cause of Earth’s mysterious deep earthquakes?
The cause of Earth’s deepest earthquakes has been a mystery to science for more than a century.
Now, a new research published in AGU Advances provides evidence that fluids play a key role in deep-focus earthquakes — which occur between 300 and 700 kilometers below the planet’s surface.
Shallow vs deep earthquakes
Most earthquakes occur close to the Earth’s surface, down to about 70 kilometers. They happen when stress builds up at a fracture between two blocks of rock — known as a fault — causing them to suddenly slide past each other.
However, deeper into the Earth, the intense pressures create too much friction to allow this kind of sliding to occur and the high temperatures enhance the ability of rocks to deform to accommodate changing stresses. Though theoretically unexpected, scientists have been able to identify earthquakes that originate more than 300 kilometers below the surface since the 1920s.
“The big problem that seismologists have faced is how it’s possible that we have these deep-focus earthquakes at all,” said Wagner. “Once you get a few tens of kilometers down, it becomes incredibly difficult to explain how we are getting slip on a fault when the friction is so incredibly high.”
Does water trigger quakes?
Ongoing work over the past several decades has shown us that water plays a role in intermediate-depth earthquakes — those that occur between 70 and 300 kilometers below Earth’s surface.
In these instances, water is released from minerals, which weakens the rock around the fault and allows the blocks of rock to slip. However, scientists didn’t think this phenomenon could explain deep-focus earthquakes, largely because it was believed that water and other fluid-creating compounds couldn’t make it far enough down into the Earth’s interior to provide a similar effect.
This thinking changed for the first time when Shirey and Wagner compared the depths of rare deep-Earth diamonds to the mysterious deep-focus earthquakes.
“Diamonds form in fluids” explained Shirey, “if diamonds are there, fluids are there.”
The diamonds themselves indicated the presence of fluids, however, they also brought samples of the deep-Earth to the surface for the scientists to study.
When diamonds form in the Earth’s interior, they sometimes capture pieces of mineral from the surrounding rock. These minerals are called inclusions and they may make your jewelry less expensive, but they are invaluable to Earth scientists. They are one of the only ways scientists can study direct samples of our planet’s deep interior.
The diamond’s inclusions had the distinct chemical signature of similar materials found in oceanic crust. This means that the water and other materials weren’t somehow created deep in the Earth’s interior. Instead, they were carried down as part of a sinking oceanic plate.
Said Wagner: “The seismology community had moved away from the idea that there could be water that deep. But diamond petrologists like Steve were showing us samples and saying ‘No, no, no. There’s definitely water down here’ So then we all had to get together to figure out how it got down there.”
The nature of deep earthquakes is one of the big questions in geoscience and the two present studies clearly show that water and other fluids are a key component of deep-focus earthquakes. [Carnegie, SSEC]
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