Where did water come from on Earth: scientists voice theories

Water reserves on Earth are incredibly important for sustaining life, but where did this water come from-was it present during the formation of the Earth, or was it delivered to the planet later by meteorites and comets from space? Scientists have examined rock samples from the Moon and have come up with the theory that the Earth was "born with water."

The source of water on Earth has been the subject of a long-standing debate among scientists. To get closer to the truth, experts from Lawrence Livermore National Laboratory (LLNL) studied the isotopic composition of lunar rocks. The results of their research are published in the journal Proceedings of the National Academy of Sciences, SciTechDaily reports.

Since the Earth-Moon system was formed together as a result of the collision of two large bodies at an early stage of the formation of the Solar System, their histories are very closely related. And since there is no plate tectonics or weathering on the Moon, this natural satellite of the Earth is a great place to find clues to the history of water on our planet.

Data from the analysis of lunar samples suggest that although the Earth and Moon were formed as a result of a giant impact, they have largely retained their original amounts of volatile elements, including water.

Despite the fact that about 70 percent of the Earth's surface is covered by water, the planet is a relatively dry place compared to many other objects in the solar system. And the moon is even drier. The conventional wisdom was that the lack of volatiles (such as water) on Earth, and especially on the Moon, was due to the same collision, and that it caused the depletion of volatiles.

But by studying the isotopic composition of lunar rocks, the team of scientists found that the bodies involved in the giant impact that formed the Earth-Moon system had very low levels of volatile elements before the impact, not because of it.

Specifically, the scientists used the relative amounts of the volatile and radioactive isotope rubidium-87 (87Rb), which is calculated from its daughter isotope strontium-87 (87Sr), to determine the balance of rubidium in the Earth-Moon system when it formed. The team found that because 87Sr was so low, the colliding bodies must have been dry from the beginning.

"The Earth was either born with the water we have or we were hit by something that was mostly pure H2O with nothing else in it. This work rules out meteorites or asteroids as possible sources of water on Earth and strongly points to the option of our planet being born with water already," said cosmochemist Greg Brenneka, co-author of the paper.

In addition, this work also shows that the large bodies that collided were from the inner part of the solar system, and this event could not have occurred earlier than 4.45 billion years ago, which significantly reduces the time window for the formation of the Moon.

"There were only a few types of materials that could have come together to create the Earth and the Moon, and they were not exotic. Most likely, they were just large bodies that formed in roughly the same area that happened to collide with each other a little more than 100 million years after the formation of the solar system. But, fortunately for us, they did just that," said Lars Borg, lead author of the study.

As OBOZREVATEL previously reported, a group of scientists from China found water in a sample of lunar soil.

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