In findings detailed in the journal Geochimica et Cosmochimica Acta, the investigators propose that water emerged primarily during Earth's later developmental phases, known as late accretion. This conclusion is significant for understanding when living conditions became possible. Scientists say that identifying when water and other key components formed helps clarify the timeline of life's origins.
"When water was delivered to the planet is a major unanswered question in planetary science," said Katherine Bermingham, an associate professor in the Department of Earth and Planetary Sciences in the Rutgers School of Arts and Sciences and lead author of the study. "If we know the answer, we can better constrain when and how life developed."
Bermingham is a cosmogeochemist who analyzes Earth rocks and meteorites to investigate the origin and evolution of the solar system. She and her colleagues used thermal ionization mass spectrometry alongside a newly designed technique to scrutinize isotopes of molybdenum. Isotopes share chemical characteristics but differ in atomic mass due to varying neutron counts.
The researchers obtained meteorite samples from the Smithsonian Institution's National Museum of Natural History. From these samples, classified as non-carbonaceous (NC) meteorites that appear to have formed in the inner solar system, they extracted molybdenum and compared the isotopic data to Earth rocks gathered in Greenland, South Africa, Canada, the United States, and Japan. These rocks date back to when Earth was finalizing its core and when the Moon is believed to have formed.
"Once we gathered the different samples and measured their isotopic compositions, we compared the meteorites signatures with the rock signatures to see if there was a similarity or a difference," Bermingham explained. "And from there, we drew inferences."
Their analyses revealed that the Earth rocks share stronger similarities with inner solar system meteorites than with those originating in outer regions. That observation, Bermingham noted, implies that much of Earth's water likely did not arrive through a large infusion during the Moon's creation, challenging a theory that this event provided a significant influx of water.
"We have to figure out from where in our solar system Earth's building blocks - the dust and the gas - came and around when that happened," Bermingham said. "That's the information needed to understand when the stage was set for life to begin."
Instead, the findings support the notion that Earth amassed water little by little following the Moon-forming period, rather than in a single step. Bermingham underscored how this reshapes the popular perspective that substantial water delivery coincided with the creation of the Moon.
"Our results suggest that the Moon-forming event was not a major supplier of water, unlike what has been thought previously," Bermingham said. "These findings, however, permit a small amount of water to be added after final core formation, during what is called late accretion."
Other co-authors from Rutgers include Linda Godfrey, an assistant research professor, and lab researcher Hope Tornebene, also in the Department of Earth and Planetary Sciences.
Research Report:The non-carbonaceous nature of Earth's late-stage accretion
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