Researchers at Rutgers-New Brunswick have discovered that water did not arrive as early in Earth’s formation as was previously believed. This discovery is crucial as it relates directly to understanding when life first appeared on our planet.
The research, published in the journal Geochimica et Cosmochimica Acta, holds significance because it indicates that water likely came during the later stages of Earth’s transformation from dust and gas into a planet, a process known to geologists as late accretion.
Scientists are keen to establish the timeline for when essential materials for life emerged to better understand the origins of life itself. Current scientific consensus identifies three critical elements that are necessary to initiate life: water, energy, and a mixture of organic chemicals collectively referred to as CHNOPS—an acronym for carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.
“Determining when water arrived on Earth is a key unanswered question in planetary science,” stated Katherine Bermingham, an associate professor in the Rutgers School of Arts and Sciences and the lead author of this research. “Understanding the timing can help us narrow down how and when life began to evolve.”
Bermingham, who specializes in cosmogeochemistry, focuses on analyzing the chemical makeup of materials within the solar system, particularly studying how the solar system and its rocky planets formed by examining both terrestrial rocks and extraterrestrial materials like meteorites.
By utilizing thermal ionization mass spectrometry alongside a novel analytical method that they developed, Bermingham and her team analyzed isotopes of the element molybdenum. Isotopes are variants of an element with the same number of protons but a differing number of neutrons, allowing them to possess the same chemical properties yet exhibit different atomic masses.
“The isotopic makeup of molybdenum in Earth rocks offers us valuable insights into the events surrounding Earth’s final core formation when the last 10% to 20% of planetary material was consolidating. This timeframe is also thought to align with the formation of the Moon,” Bermingham explained.
The research team extracted molybdenum from meteorite samples from the National Museum of Natural History at the Smithsonian Institution. Meteorites are categorized into two main types: the “CC” group, which suggests formation in the outer, likely wetter regions of the Solar System, and the “NC” group, which indicates that these meteorites originated from the inner, presumably drier, solar system. This study specifically concentrated on NC group samples.
They compared the isotopic composition of molybdenum from these meteorites with Earth rock samples collected from locations in Greenland, South Africa, Canada, the United States, and Japan by field geologists. The molybdenum in these terrestrial rocks is typically regarded as having been added to Earth around the time the Moon was formed, coinciding with final core formation—exactly the period they wanted to investigate regarding the origins of water.
“After gathering the various samples and analyzing their isotopic compositions, we examined the similarities and differences between the meteoritic signatures and those of the rocks,” Bermingham said. “From this comparison, we drew our conclusions.”
The results indicated that the Earth rocks they analyzed were more akin to the inner solar system meteorites (NC) rather than their outer solar system counterparts (CC).
“We need to determine the origins of Earth’s building blocks—namely, the dust and gas—and the timing of this process,” Bermingham stated. “This information is vital for understanding when the conditions for life began to emerge.”
Since the chemical composition of the studied Earth rocks closely aligns with the attributes of the presumed inner solar system meteorites, the scientists concluded that Earth likely did not receive a significant amount of water during the Moon-forming events as previously thought. Bermingham noted that, traditionally, it was believed a considerable portion of Earth’s water came from this event.
However, their findings suggest that the majority of Earth’s water likely arrived in smaller amounts after the Moon had formed, implying a much later period in Earth’s development.
“Our findings indicate that the Moon-forming event was not a significant source of water, contrary to previous beliefs,” said Bermingham. “Instead, our results suggest a limited amount of water could have been delivered post final core formation, during what is known as late accretion.”
Other contributors from Rutgers to this study include Linda Godfrey, an assistant research professor, and laboratory researcher Hope Tornebene, both affiliated with the Department of Earth and Planetary Sciences.
