The Moon, our natural satellite, has witnessed impressive geological events since its formation. According to a recent study published in the journal Nature by an international team of researchers from the University of California, Santa Cruz, the Max Planck Institute for Solar System Research, and the Collège de France, the Moon experienced volcanic activity so intense during its first few hundred million years that its crust melted several times. This finding not only redefines our understanding of its formation but also resolves several mysteries about its age.

Between 4.43 and 4.51 billion years ago, the Moon emerged following a colossal collision between the primitive Earth and a body roughly the size of Mars. This impact generated extreme heat that vaporized and ejected material into space, creating an ocean of molten rock that eventually solidified to form the Moon. In its early days, the satellite orbited much closer to Earth than it does today, intensifying tidal forces between the two bodies. These interactions not only altered the Moon’s orbit, making it more elliptical, but also generated heat within the Moon’s interior, fueling unprecedented volcanic activity.

A comparable example can be observed today on Io, one of Jupiter’s moons, which is the most volcanically active body in the Solar System due to Jupiter’s gravitational forces. However, the early Moon possibly rivaled Io in terms of volcanic activity, showcasing the impact of tidal forces on the internal dynamics of a celestial body.

Moon older
Hypothesized timeline of events. Credit: F.Nimmo et al.

The Moon’s volcanic activity directly affected the dating of its rocks. Lunar minerals contain radioactive isotopes that act as natural clocks, allowing scientists to calculate the age of rocks by measuring the concentration of these isotopes. However, when rocks are exposed to extreme temperatures, such as those caused by volcanism, the isotopes can mix with the environment, resetting this geological clock.

According to the study, the intense volcanic activity melted the lunar crust multiple times, erasing traces of its original formation. Only a few minerals, such as the resilient zircon crystals, survived these extreme conditions intact, preserving evidence of the Moon’s most ancient past.

This new interpretation resolves key contradictions in estimates of the Moon’s age. While most lunar rock samples indicated a younger age, zircon crystals pointed to an older formation, creating discrepancies in existing theories. Moreover, the relative scarcity of craters on the Moon’s surface, which seemed to indicate a less prolonged history, is now explained by the filling of early impact basins with lava, making them unrecognizable.

Additionally, differences in composition between the Moon’s mantle and Earth’s mantle had puzzled scientists. The study suggests that a new cycle of melting within the Moon’s interior allowed certain elements to escape toward its iron core, altering the mantle’s composition. Thus, all pieces of the lunar puzzle, from its formation to its volcanic evolution, finally fit into a coherent model.

SOURCES

Max Planck Institute for Solar System Research

Nimmo, F., Kleine, T. & Morbidelli, A. Tidally driven remelting around 4.35 billion years ago indicates the Moon is old. Nature 636, 598–602 (2024). doi.org/10.1038/s41586-024-08231-0

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