Privileged Planet: water and subduction (Introduction)

by David Turell , Monday, November 19, 2018, 22:00 (1984 days ago) @ David Turell

The subduction zones drag lots of water into the mantle:

https://www.livescience.com/64091-earth-is-eating-its-oceans.html?utm_source=ls-newslet...

"As Earth's tectonic plates dive beneath one another, they drag three times as much water into the planet's interior as previously thought.

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"The find has major ramifications for understanding Earth's deep water cycle, wrote marine geology and geophysics researcher Donna Shillington of the Lamont-Doherty Earth Observatory at Columbia University in an op-ed accompanying the new paper. Water beneath the surface of the Earth can contribute to the development of magma and can lubricate faults, making earthquakes more likely, wrote Shillington, who was not involved in the new research.

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"Water is stored in the crystalline structure of minerals, Shillington wrote. The liquid gets incorporated into the Earth's crust both when brand-new, piping-hot oceanic plates form and when the same plates bend and crack as they grind under their neighbors.

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"'Before we did this study, every researcher knew that water must be carried down by the subducting slab," Cai told Live Science. "But they just didn't know how much water."

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"Using the measured velocities, along with the known temperatures and pressures found there, the team calculated that the subduction zones pull 3 billion teragrams of water into the crust every million years (a teragram is a billion kilograms).

"Seawater is heavy; a cube of this water 1 meter (3.3 feet) long on each side would weigh 1,024 kilograms (2,250 lbs.). But still, the amount pulled down by subduction zones is mind-boggling. It's also three times as much water as subduction zones were previously estimated to take in, Cai said.

"And that raises some questions: The water that goes down must come up, usually in the contents of volcanic eruptions. The new estimate of how much water is going down is larger than estimates of how much is being emitted by volcanos, meaning scientists are missing something in their estimates, the researchers said. There is no missing water in the oceans, Cai said. That means the amount of water dragged down into the crust and the amount spouted back out should be about equal. The fact that they aren't suggests that there's something about how water moves through the interior of Earth that scientists don't yet understand."

Comment: All of Earth's mechanisms are circular feedback loops to maintain the stability of the Earth as it evolves with additional living forms in number and variety. It all looks carefully designed to me.