Meteorite study suggests Earth may have been wet since it formed
Enstatite chondrite meteorites, once considered 'dry,' contain enough
water to fill the oceans -- and then some

Date:
August 27, 2020
Source:
Washington University in St. Louis
Summary:
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 suggest that Earth may have
always been wet.



FULL STORY ==========================================================================
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 Petrographiques et Geochimiques (CRPG, CNRS/Universite 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."
The findings from this study are surprising because the Earth's building
blocks are often presumed to be dry. They come from inner zones of the
solar system where temperatures would have been too high for water to
condense and come together with other solids during planet formation.

The meteorites provide a clue that water didn't have to come from
far away.



==========================================================================
"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.

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.

"If enstatite chondrites were effectively the building blocks of our
planet - - as strongly suggested by their similar isotopic compositions --
this result implies that these types of chondrites supplied enough water
to Earth to explain the origin of Earth's water, which is amazing!" Vacher said.

The paper also proposes that a large amount of the atmospheric nitrogen
-- the most abundant component of the Earth's atmosphere -- could have
come from the enstatite chondrites.

"Only a few pristine enstatite chondrites exist: ones that were not
altered on their asteroid nor on Earth," Piani said. "In our study we
have carefully selected the enstatite chondrite meteorites and applied
a special analytical procedure to avoid being biased by the input of terrestrial water." Coupling two analytical techniques -- conventional
mass spectrometry and secondary ion mass spectrometry (SIMS) -- allowed researchers to precisely measure the content and composition of the
small amounts of water in the meteorites.

Prior to this study, "it was commonly assumed that these chondrites
formed close to the sun," Piani said. "Enstatite chondrites were thus
commonly considered 'dry,' and this frequently reasserted assumption
has probably prevented any exhaustive analyses to be done for hydrogen."

========================================================================== Story Source: Materials provided by
Washington_University_in_St._Louis. Original written by Talia
Ogliore. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Laurette Piani, Yves Marrocchi, Thomas Rigaudier, Lionel G. Vacher,
Dorian Thomassin, Bernard Marty. Earth's water may have
been inherited from material similar to enstatite chondrite
meteorites. Science, 2020 DOI: 10.1126/science.aba1948 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200827141334.htm

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