Oceans inside the Earth
According to a geologist from the University of Colorado at Boulder, the interior of the earth, locked in countless crystals, could contain as much water as can fit in three to five oceans. These oceans may help regulate the level of water at the earth's surface. 10 years ago Professor Joseph Smyth discovered that a mineral called wadsleyite lying about 400 to 560 kilometers below the surface of the earth might contain water. However, this water is not in liquid form, but is firmly bound to the crystals as a component of them.
Generally, rock on Earth is fairly dry - much drier than, for example, meteorites, which also contain wadsleyite. Rocks usually consist of only one percent water. Wadsleyite, on the other hand, contains 3.3 percent water. That doesn't seem like much, but given the amount of wadsleyite the scientists say is in the Earth, that would be three to five times the total amount of water on our planet's surface, says Smyth. His question is: "Is this how the earth regulates the amount of water on the surface?"
The wadsleyite in the mantle is exposed to a pressure of about 21 million kg/m² and a temperature of about 1650 °C. It is in the upper half of the transition zone between the upper and lower mantle. The Earth's mantle bends upwards and breaks through volcanic openings in the deep sea ridge in the middle of the ocean, i.e. where the continental plates separate, through to the earth's surface. In the opposite direction, the water may be transported into the upper mantle through subduction zones. Subduction zones are where the plates merge. In this region, according to Smyth, the wadsleyite could store large amounts of water. With rising convection currents, the wadsleyite could then melt, releasing water vapor into the oceans as the molten rock cools.
It has already been calculated how much wadsleyite is in the ground. But the big question is: how much water does wadsleyite really contain? Smyth is currently trying to answer this with laboratory tests. For his experiments, he makes wadsleyite in the laboratory by squeezing two diamonds together in a vise. A pressure of about 21 million kg/m² is created. Smyth then X-rays the sample to determine water content and other physical properties. How fast the mineral transmits seismic waves depends on the amount of water in the wadsleyite. If seismic waves sent through the earth have the same speed, scientists know how much water is hidden inside the earth.
The Earth's oceans have existed for at least four billion years. Their volume has remained almost constant over the past 500 million years. According to Smyth, the "inner oceans" may play a role in regulating the amount of water.
In 1996, Smyth also discovered what is known as wadsleyite II, which can store water under even greater pressure in a deeper section of the transition zone.
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