Earth’s Water May Be Older Than We Thought

A recent study by a research team from the University of Göttingen and the Max Planck Institute for Solar System Research (MPS) has uncovered groundbreaking evidence that reshapes our understanding of both the formation of the Moon and the early development of water on Earth. The findings suggest that the Moon likely formed from material ejected from the Earth’s mantle, challenging the prevailing theory that a cosmic collision with a protoplanet known as Theia was the primary cause of the Moon’s formation. Additionally, the new evidence supports the idea that water could have been present on Earth earlier in its history, challenging long-held assumptions about the origins of Earth’s water.

Revisiting the Moon’s Origin

The dominant theory regarding the Moon’s formation has long been based on the idea that Earth collided with a large body, believed to be the protoplanet Theia, around 4.5 billion years ago. According to this theory, the collision resulted in debris being ejected from both Earth and Theia, which eventually coalesced to form the Moon. While this scenario has long been supported by many in the scientific community, there have been lingering questions—especially concerning the isotopic similarities between Earth and the Moon that could not be easily explained by the standard theory.

The new research sheds light on this issue. Through the analysis of oxygen isotopes, specifically oxygen-17 (17O), found in both lunar and Earth samples, the researchers identified a significant similarity in the isotopic compositions of the two bodies. The research team carried out measurements on 14 samples from the Moon and 191 measurements on minerals from Earth, using an improved version of laser fluorination, a cutting-edge technique in which oxygen is released from rocks via the heat of a laser. The similarities in oxygen isotopes, especially 17O, between Earth and the Moon were striking and presented a significant challenge to the theory that Theia played a larger role in the Moon’s formation.

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Traditionally, the isotope disparity between Earth and the Moon had been one of the biggest mysteries in cosmochemistry, leading to what is known as the “isotope crisis.” This dilemma involved the difficulty of explaining how the two bodies could share such a high degree of isotopic similarity, especially considering that they were believed to have formed from different sources.

The team’s findings, published in the Proceedings of the National Academy of Sciences, indicate that a more plausible explanation is that Theia, in the event of the collision, may have lost its rocky mantle during earlier impacts with other objects in the solar system. As a result, when Theia collided with Earth, it may have come in at a much smaller scale—essentially as a “metallic cannonball” largely composed of metal, without its mantle, thus leaving Earth as the primary source of material for the Moon’s formation.

Professor Andreas Pack, the study’s co-author and Managing Director of Göttingen University’s Geoscience Centre, suggests that this theory could resolve the long-standing isotope paradox: “If this were the case, Theia would have contributed primarily to Earth’s core, while the Moon would have formed mostly from material ejected from Earth’s mantle.” This conclusion provides a more straightforward explanation for the similarity in isotopic composition between Earth and the Moon.

Rewriting the History of Water on Earth

The study’s findings also shed new light on the history of water on Earth. Conventional theories have posited that Earth’s water came from a period of bombardment during the Late Veneer Event, a time when a multitude of impacts, likely from meteorites and comets, brought water to Earth. The assumption was that, because the Moon was not impacted as frequently as Earth, there would be noticeable differences in the oxygen isotopic ratios between the two bodies, depending on whether or not the water came from these late impacts. However, the new research suggests that Earth’s water could have arrived earlier in its history, and it may not have been solely the result of these late impacts.

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The team’s new data challenges the “late veneer hypothesis.” As noted by the study’s lead author Meike Fischer, who was working at MPS at the time, “Since the new data shows that both Earth and the Moon share a similar isotopic composition, many types of meteorites—previously thought to be the source of Earth’s water—can be ruled out.” This finding is significant, as it effectively dismisses the idea that water on Earth was delivered exclusively through late bombardments.

According to Fischer, the isotopic similarity points toward a different source for Earth’s early water: “Our data can be explained particularly well by a class of meteorites known as ‘enstatite chondrites.’ These meteorites are isotopically similar to Earth and contain sufficient quantities of water to suggest that they were a major contributor to Earth’s water supplies.” Enstatite chondrites are a rare class of meteorites that differ from other meteorite types by their unique oxygen isotope signatures, which match the Earth’s composition.

This finding is revolutionary because it places enstatite chondrites at the center of the story of Earth’s water. Unlike other meteorites, which had higher levels of oxygen-17 that did not align with Earth’s isotopic signature, enstatite chondrites closely match the oxygen isotope ratios found on Earth, reinforcing the idea that they could have played a crucial role in delivering water to our planet during the early stages of the solar system.

Implications and Future Research Directions

The findings presented by the researchers from the University of Göttingen and the Max Planck Institute for Solar System Research represent a significant shift in how scientists approach both the Moon’s formation and the origins of Earth’s water. The discovery that Theia may have had less of an impact on the Moon’s formation than previously believed helps simplify our understanding of the early Earth-Moon system. Furthermore, by ruling out a major role for late veneer impacts in bringing water to Earth, the study opens new avenues for exploring the delivery of water through other means, such as the contributions from enstatite chondrites and other early solar system bodies.

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Moreover, the implications of these findings extend beyond lunar and Earth sciences. Understanding the origins of water on Earth helps inform the search for water—and the potential for life—on other planets and moons. This research underscores the importance of isotopic analysis in planetary science, not only in understanding the history of our own Solar System but also in answering broader questions about the chemical processes that may have taken place on other terrestrial planets and moons.

As the field of cosmochemistry evolves, this research could inspire future investigations aimed at refining our models of planetary formation, water delivery mechanisms, and the very origins of life in the Universe.

Conclusion

The latest findings from the University of Göttingen and the Max Planck Institute for Solar System Research present an exciting new chapter in our understanding of the Moon’s formation and the early history of water on Earth. The research overturns traditional theories and sheds light on the fascinating processes that have shaped our planet and its satellite. As scientists continue to explore the many mysteries of the cosmos, studies like these remind us that the story of Earth and its Moon is far more complex—and much more intertwined with our planet’s unique isotopic fingerprints—than previously understood.

Reference: Meike Fischer et al, Oxygen isotope identity of the Earth and Moon with implications for the formation of the Moon and source of volatiles, Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2321070121

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