Earth’s Water Has Been Here Far Longer Than Previously Believed, Claims New Study

Chuck Bednar for – Your Universe Online
The water that covers over 70 percent of the Earth formed just 14 million years after the formation of the solar system – much earlier than previously believed, according to a new study led by Woods Hole Oceanographic Institution (WHOI) scientists and published online Friday in the journal Science.
“The answer to one of the basic questions is that our oceans were always here. We didn’t get them from a late process, as was previously thought,” lead author Adam Sarafian, an MIT/WHOI Joint Program student in the Geology and Geophysics Department, said in a statement.
One commonly held belief, according to the researchers, was that Earth and other worlds were completely dry when they formed due to the fact that planetary formation is a high-energy and high-impact process. Under this hypothesis, water would have arrived later from comets or “wet” asteroids composed of ice and gases.
“With giant asteroids and meteors colliding, there’s a lot of destruction,” noted co-author Horst Marschall, a geologist at WHOI. “Some people have argued that any water molecules that were present as the planets were forming would have evaporated or been blown off into space, and that surface water as it exists on our planet today, must have come much, much later – hundreds of millions of years later.”

Image Above: In this illustration of the early solar system, the dashed white line represents the snow line—the transition from the hotter inner solar system, where water ice is not stable (brown) to the outer Solar system, where water ice is stable (blue). Two possible ways that the inner solar system received water are: water molecules sticking to dust grains inside the “snow line” (as shown in the inset) and carbonaceous chondrite material flung into the inner solar system by the effect of gravity from protoJupiter. With either scenario, water must accrete to the inner planets within the first ca. 10 million years of solar system formation. (Illustration by Jack Cook, Woods Hole Oceanographic Institution)
Sarafian, Marschall and their colleagues opted instead to examine another potential source of Earth’s water – ancient, unaltered meteorites known as carbonaceous chondrites that were formed in the same dust, ice and gas particle clouds involved in the sun’s formation roughly 4.6 billion years ago, long before the planets formed. Carbonaceous chondrites resemble much of the bulk solar system composition, contain a lot of water and have previously been considered as candidates for the origin of Earth’s water, the study authors noted.
“In order to determine the source of water in planetary bodies, scientists measure the ratio between the two stable isotopes of hydrogen: deuterium and hydrogen,” WHOI explained. “Different regions of the solar system are characterized by highly variable ratios of these isotopes. The study’s authors knew the ratio for carbonaceous chondrites and reasoned that if they could compare that to an object that was known to crystallize while Earth was actively accreting then they could gauge when water appeared on Earth.”
As part of their research, the team analyzed meteorite samples from the planetoid Vesta, explained Irene Klotz of Discovery News. The samples from Vesta, which were provided to the team by NASA and are known as eucrites, demonstrated hydrogen isotope rations matching those found in carbonaceous chrondrites, and previous research revealed that those carbonaceous chrondrites match the chemical fingerprints of Earth’s hydrogen.
The chemical signatures of the eucrites belong to one of the oldest hydrogren reservoirs in the solar system, and according to the study authors, their age (14 million years after the formation of the solar system) makes them ideal for the source of the water present in the inner solar system while the Earth was forming. The research team analyzed five different samples, and by combining those results with nitrogen isotope data, they concluded that the carbonaceous chondrites were indeed the most likely common source of water for both Earth and Vesta.
Based on that conclusion, Sarafian and his colleagues argue that the origin of water actually dates back to roughly 4.6 billion years ago, during a time when the planets of the inner solar system were still forming, according to National Geographic reporter Andrew Fazekas. While they are not eliminating the possibility that some of Earth’s water may have arrived later and from a different source, their findings indicate that there would have been enough H2O available on the planet for life to have begun earlier than previously believed, Fazekas added.
“An implication of that is that life on our planet could have started to begin very early,” explained co-author Sune Nielsen, an assistant scientist in the WHOI geology and geophysics program. “Knowing that water came early to the inner solar system also means that the other inner planets could have been wet early and evolved life before they became the harsh environments they are today.”
Related Reading:
> Meteorites Source Of Earth’s Water, New Study Suggests
> Meteorite – Universe Reference Library
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