Guest oy vey by David Middleton
First we learn that climate change is dissolving the seafloor and now we find out that Earth is devouring its own oceans (like it could be devouring some other planet’s oceans)… And it’s three times as bad as “previously thought” (is it ever three times better than previously thought?).
Live Science Planet Earth
The Earth Is Eating Its Own Oceans
By Stephanie Pappas, Live Science Contributor | November 14, 2018
As Earth’s tectonic plates dive beneath one another, they drag three times as much water into the planet’s interior as previously thought.
Those are the results of a new paper published today (Nov. 14) in the journal Nature. Using the natural seismic rumblings of the earthquake-prone subduction zone at the Marianas trench, where the Pacific plate is sliding beneath the Philippine plate, researchers were able to estimate how much water gets incorporated into the rocks that dive deep below the surface. [In Photos: Ocean Hidden Beneath Earth’s Surface]
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.
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.
“Many more studies need to be focused on this aspect,” Cai said.
Well, at least they aren’t blaming this on climate change or President Trump.
All seriousness aside, this is how plate tectonics work. In the absences of oceans, plate tectonics might not be possible.
Water plays an important role in mantle convection. In the ductile creep regime, the viscosity of wet rocks is weaker than the viscosity of dry rocks by several orders of magnitude. In the brittle regime, the most substantial effect is probably serpentinization which can reduce the friction coefficient by a factor of 2 or more. The difference between the strength of a wet lithosphere and that of a dry lithosphere seems to be big enough to control the very existence of plate tectonics. Because of dehydration due to partial melting the oceanic lithosphere is expected to be essentially dry above some critical depth, around 60-80 km. This would make the lithosphere strong enough to prevent plate motion. Percolation of water from the surface can be the main mechanism supplying water to the upper parts of the lithosphere. This implies that liquid water can be crucial for maintaining plate tectonics. On the other hand, the surface temperature is above the freezing point because of the greenhouse gases such as carbon dioxide. A simple model shows that if the blackbody temperature of the Earth is slightly below the freezing point of water, the feedback between plate tectonics, volcanism, and water and carbon cycles can result in an equilibrium state in which the surface temperature is established within the stability field of liquid water.
The fact that there’s no water missing from the oceans simply means that the Earth must also be spewing out three times as much water vapor (and other gases) from volcanic sources than previously thought. One of the “other gases” emitted by volcanoes is the evil, climate wrecking carbon dioxide. Wouldn’t it be “funny” if volcanoes accounted for three times as much of the CO2 in the atmosphere than previously thought? But then again, they wouldn’t notice it… because volcanoes aren’t in the flashlight beam…
The article was actually fairly well written, but the headline was simply stupid.
The role that subducted water plays in plate tectonics isn’t really a “new thing.” Why on Earth would a competent science journalist title the article, “The Earth Is Eating Its Own Oceans”?
Stephanie Pappas, Live Science Contributor
Stephanie Pappas is a contributing writer for Live Science. She covers the world of human and animal behavior, as well as paleontology and other science topics. Stephanie has a Bachelor of Arts in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz. She has ducked under a glacier in Switzerland and poked hot lava with a stick in Hawaii. Stephanie hails from East Tennessee, the global center for salamander diversity.