A hydrogen “river” that crossed paths with the Earth during its formation might have been the source of water on our planet. According to a thesis presented in an article in the scientific publication Journal of Geophysical Research: Planets, a nebula stemmed from the Sun carried a large amount of hydrogen through the solar system and, when it crashed into the Earth, the gas combined with oxygen resulted in a spontaneous chemical reaction that ended up as the formula of water: H2O.

“Since water is nothing but hydrogen + oxygen, and oxygen was already abundant on our planet, any source of hydrogen could have served as the origin of water on Earth,” states Steven Desch, coauthor of the study and astrophysicist of the State University of Arizona. “However, the Earth might have been formed with an extra source of hydrogen with less deuterium (heavier hydrogen) in the mixture of hydrogen atoms. Therefore, the only possible source is gas from a solar nebula”, he explained in an interview to Popular Science.

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The allegation is that the gas held inside the nebula was incorporated by the core of the planet, which until that moment was composed of a solid core covered with ocean magma. This core captured a large amount of hydrogen, which was gradually released and, as it mixed with the existing oxygen in the earthly atmosphere, formed the first primitive oceans of water.

Most of the hydrogen volume is still attached to the core of the Earth. It is estimated that the Mantle of the planet contains the equivalent to the volume of water of two earthly oceans; in the core, there would be the equivalent to up to five earthly oceans of water.

To reach this conclusion, Desch and his team designed a computerized model of the Earth in the period, related to its formation, and added hydrogen of an equivalent composition to the solar nebula. The model simulation produced by the software reached a result that matches some samples of rocks collected from the mantle of the earthly magma.

Therefore, the result of the study shows that one out of every 100 molecules of water on Earth came from a solar nebula – according to the article, the rest matches the most accepted hypothesis that water reached our planet via asteroids and comets.

Asteroids and comets: another source of water

Published on the Journal of Geophysical Research: Planets, the breakthrough is not the first to establish an explanation for the presence of water on Earth. It also offers a demonstration in accordance with the hypothesis of comets and asteroids.

A crucial factor to think about the origin of water on Earth is the mixture between deuterium atoms (heavy hydrogen, chemical symbol D) and conventional hydrogen (chemical symbol H).  Water from the global ocean has a mixture D/H of 150 parts per million (ppm), similar to the mixture found in the water of asteroids, around 140 ppm in the D/H mixture.

 In the solar nebula, the mixture D/H is considerably inferior, of 21 ppm, and for this reason, the hypothesis that took it for consideration was abandoned. The computerized model that served as the basis for the study, however, shows that the Earth may have gone through a series of geochemical processes that increased the D/H mixture of the hydrogen collected from the nebula. Thus, they would be the first source of water on the Earth, afterward added to more water originating from asteroids.

“Even planets that form far away from sources of water-rich asteroids may still have water,” he says. “Not as much as Earth, perhaps, but there is a floor of about 0.1 to 0.2 oceans’ worth of hydrogen – applicable to Venus and many other exoplanets, he concluded in the Popular Science interview.

Content published in January 28, 2019