Issued on: Change:
Washington (AFP)
Water occupies 70 percent of the earth’s surface and is crucial to life as we know it, but how it got here has been a long scientific debate.
The puzzle was a step closer to the resolution on Thursday after a team of French scientists reported in the journal Science that they had identified which space rocks may have been responsible.
Cosmochemist Laurette Piani, who led the investigation, told AFP that, contrary to the theories being heard, the Earth’s water may have already been in the building blocks.
According to early models of how the solar system came into being, the large disks of gas and dust that revolved around the sun and eventually formed the inner planets were too hot to form ice.
This would explain the barren conditions on Mercury, Venus and Mars – but not our blue planet, with its vast oceans, humid atmosphere and well-hydrated geology.
The most common idea is that water was later brought by extraterrestrial objects, and the main suspect was water-rich meteorites known as carbonaceous chondrites.
But the problem was that their chemical composition did not closely match the rocks of our planet.
They also formed in the outer solar system, making it less likely that they could have fallen to the early Earth.
Another type of meteorite, called enstatite chondrites (ECs), is a much closer chemical similarity, indicating that these were the building blocks of the Earth and the other inner planets.
However, because these rocks formed close to the sun, they were thought to be too dry to account for the Earth’s rich reservoirs.
To test whether this was true, Piani and her colleagues at the University of Lorraine used a technique called mass spectrometry to measure the hydrogen content in 13 enstatite chondrites.
They found that the rocks contained enough hydrogen to supply the earth at least three times the water mass of its oceans.
They also measure the two types of hydrogen, known as isotopes, because their relative proportion is very different from one solar system object to another.
“We found the hydrogen isotopic composition of enstatite chondrites comparable to that of the water stored in the mantle,” Piani said, comparing it to a DNA match.
She added that research does not rule out subsequent addition of water by other sources such as comets, but indicates that enstatite chondrites significantly contributed to the Earth’s water budget at the time it formed.
The work “brings a crucial and elegant element to this puzzle,” wrote Anne Peslier, a planetary scientist for NASA, in an accompanying editorial.
© 2020 AFP
