Analysis of samples from the moon, collected as part of the Apollo program, shows that meteorites that reached Earth may have contained limited amounts of water, which casts doubt on the prevailing hypothesis about the origin of Earth's oceans.
As is well known, it has long been believed that most of Earth's water arrived on our planet via asteroids and comets that collided with it between 4 and 3.8 billion years ago. Scientists thought that the young Earth's proximity to the Sun prevented it from retaining the volatile materials. However, a study by a research team led by Dr. Tony Gargano of the Lunar and Planetary Institute in the United States offers a different perspective on this hypothesis.
The key to this puzzle lies in the Moon, whose surface has not been subjected to tectonic processes like Earth's, allowing it to preserve traces of ancient impacts. Researchers focused on analyzing the trivalent isotopic composition of oxygen in lunar soil samples brought back by astronauts. This method allowed them to separate signals originating from meteoritic material from traces of vaporization resulting from impact events.
The measurements showed that at least 1 percent of the mass of the studied samples consists of meteoritic material, likely carbonaceous, which was partially vaporized by the impact.
Based on this data, scientists estimated the maximum amount of water that meteorites may have delivered to the Earth-Moon system over the past billions of years. This amount is minuscule compared to the mass of Earth's hydrosphere, estimated at about 1.46 sextillion kilograms. While this doesn't mean meteorites didn't contribute to water at all, their role as a primary source of Earth's oceans is now considered unlikely.
For his part, Dr. Justin Simon of NASA's Earth and Ocean Research Division points out that the Moon's long-term geological record makes it unlikely that meteorites that fell during the later stages of its history were the primary source of Earth's ocean water. This discovery raises renewed questions about how and when the elements necessary for the emergence of life on our planet accumulated.
The study's findings were published in the journal Proceedings of the National Academy of Sciences.
