Earth’s water supply is vital to its ability to sustain life, but where does this water come from? Did they exist when the Earth was formed or were they later delivered from space by meteorites or comets?

The source of Earth’s water has long been a matter of debate, and scientists at Lawrence Livermore National Laboratory (LLNL) think they have the answer—and they found it by examining moon rocks.

Since the Earth-Moon system was formed long ago under the impact of two large bodies, their history is closely intertwined with the history of the Solar System. And since the Moon lacks plate tectonics and atmospheric conditions, processes that tend to erase or obscure evidence on Earth, the Moon is indeed the perfect place to look for clues to Earth’s water history. Earth.

Although about 70% of Earth’s surface is covered by water, the planet in general is a relatively dry place compared to many other objects in the Solar System. The moon is drying up. Conventional wisdom was that the lack of volatile species (such as water) on Earth – particularly the Moon – was due to such a violent impact that the volatiles were depleted.

But by examining the isotopic composition of Moon rocks, the team found that the objects involved in the impact that shaped the Earth-Moon system had previously very low levels of volatile elements, rather than collisions. , Specifically, the team identified the volatile, radioactive isotope rubidium-87 (⁸⁷Rb), which is calculated from its daughter isotope strontium-87 (⁸⁷Sr), to determine the Rb budget in the Earth-Moon system during its formation. the team found him because ⁸⁷The Seine, an indicator of the Moon’s long-term fluctuating budget, was very low, and the objects that collided would have been dry at first, and little could have been added since.

“The Earth was either born out of the water we had, or we were influenced by something that was essentially pure₂Oh there’s not much in it. Cosmic chemist Greg Brainica, a co-author of the paper, said the work rules out meteorites or asteroids as potential sources of water on Earth and strongly points to a “born with” option.

In addition to greatly narrowing down the potential source of Earth’s water, this work further suggests that large colliding objects may have come from the inner Solar System, and the event could not have occurred 4 years earlier. .45 billion years, which greatly reduces the formation of . Moon window.

According to the study’s lead author, Lars Berg: “There was only a small amount of material that could combine to form the Earth and the Moon, and this was not strange – it is likely that the two were large bodies that were roughly the same.” The regions that collided more than a year later, 100 million years after the formation of the Solar System… But we’re lucky they did.

References: Lars E. Berg, Gregory A. Bernica and Thomas S. “The Origin of Volatile Elements in the Earth-Moon System” by Kroyer, 14 February 2022 Available here. Proceedings of the National Academy of Science,
DOI: 10.1073/pns.2115726119

appears in search Proceedings of the National Academy of Science, LLNL scientist Thomas Kruijer also contributed to the research. the work was funded by NASA and a laboratory based research and development program.