Earth’s Water May Have Come From… Earth

Guest “full circle” by David Middleton

Way back in the Pleistocene, when I was a young geology student with hair, we were taught that the most likely source of Earth’s water was volcanic out-gassing. The water that fills our oceans, enables plate tectonics and made life possible, was thought to have originated inside the Earth and was expelled by volcanoes as water vapor. Then there was a cavalcade of comets… My recollection is that sometime after Walter and Luis Alvarez demonstrated that a big chunk of space rock took out the non-avian dinosaurs, meteors and comets were suddenly the cause of everything… kind of like CO2. The new paradigm was that water and, perhaps life itself, was brought to Earth by comets bombarding the Earth over billions of years… Then someone took a hard look at enstatite chondrite meteorites:

Meteorite study suggests Earth may have always been wet
Enstatite chondrite meteorites, once considered ‘dry,’ contain enough water to fill oceans

By Talia Ogliore August 27, 2020

A new study finds that Earth’s water may have come from materials that were present in the inner solar system at the time the planet formed — instead of far-reaching comets or asteroids delivering such water. The findings published Aug. 28 in Science suggest that Earth may have always been wet.

Researchers from the Centre de Recherches Pétrographiques et Géochimiques (CRPG, CNRS/Université de Lorraine) in Nancy, France, including one who is now a postdoctoral fellow at Washington University in St. Louis, determined that a type of meteorite called an enstatite chondrite contains sufficient hydrogen to deliver at least three times the amount of water contained in the Earth’s oceans, and probably much more.

Enstatite chondrites are entirely composed of material from the inner solar system — essentially the same stuff that made up the Earth originally.

“Our discovery shows that the Earth’s building blocks might have significantly contributed to the Earth’s water,” said lead author Laurette Piani, a researcher at CPRG. “Hydrogen-bearing material was present in the inner solar system at the time of the rocky planet formation, even though the temperatures were too high for water to condense.”

[…]

Enstatite chondrites are rare, making up only about 2 percent of known meteorites in collections.

But their isotopic similarity to Earth make them particularly compelling. Enstatite chondrites have similar oxygen, titanium and calcium isotopes as Earth, and this study showed that their hydrogen and nitrogen isotopes are similar to Earth’s, too. In the study of extraterrestrial materials, the abundances of an element’s isotopes are used as a distinctive signature to identify where that element originated.

[…]

Washington University in St. Louis

Enstatite chondrites are thought to have formed in the inner solar system, where Earth was formed. It’s long been interpreted that Earth and Enstatite chondrites formed from essentially the same material. Until recently, it was thought that enstatite chondrites were devoid of water because they formed too close to the Sun.

“The most interesting part of the discovery for me is that enstatite chondrites, which were believed to be almost ‘dry,’ contain an unexpectedly high abundance of water,” said Lionel Vacher, a postdoctoral researcher in physics in Arts & Sciences at Washington University in St. Louis.

Vacher prepared some of the enstatite chondrites in this study for water analysis while he was completing his PhD at Universite de Lorraine. At Washington University, Vacher is working on understanding the composition of water in other types of meteorites.

Science Daily

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August 28, 2020 at 08:58PM

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