A team of planetary scientists has revealed evidence of a massive asteroid impact on the moon that occurred around 3.5 billion years ago, offering a rare glimpse into the violent early history of the inner solar system. The findings, published in Geology, link this lunar event to similar impacts on Earth and in the asteroid belt, providing crucial insight into the conditions shaping the emergence of life on our planet.
Mining Lunar Clues to Earth’s Earliest Years
Earth’s earliest geological record is largely erased due to erosion, subduction, and tectonic activity, leaving scientists with few direct clues about the planet’s first billion years. To study this era, researchers turn to the moon, which preserves a relatively stable record of asteroid impacts. Lunar meteorites, such as NWA 12593 found in northwest Africa, act as time capsules, carrying evidence of collisions that shaped both the moon and Earth.
According to Carolyn Crow, a planetary scientist at the University of Colorado Boulder, understanding these impacts is key to deciphering early life’s resilience:
“On Earth, the first fossil evidence of life shows up around 3.5 billion years ago, meaning that life is emerging and evolving before then. The question that we often have, even going back further, is what was the impact record when life was emerging?” She adds, “It is important for understanding how life is taking hold, how life is emerging. The cadence of these catastrophic events is an important part of the equation.”
The First Giant Impact: Molten Moonscapes
Radiometric analysis of NWA 12593 reveals evidence of a colossal impact event roughly 3.5 billion years ago. The collision was energetic enough to turn the lunar surface into a molten sheet, forming minerals that only crystallize at extreme temperatures, including a rare form of cubic zirconia. Unlike the synthetic gemstones used in jewelry, these natural crystals survive fleetingly under normal conditions, leaving subtle traces called cubic zirconia phase heritage.
This first impact represents one of the earliest and most violent events in the moon’s history. Its intensity reshaped local geology and left a mark that can still be studied billions of years later, illustrating the scale of cosmic forces at work during the early solar system.
This remarkable discovery, detailed in a 2026 study published in Geology, provides one of the clearest records of the moon’s earliest violent collisions and links these impacts to similar events on Earth and in the asteroid belt
Breccias: Nature’s Cosmic Concrete
The meteorite also preserves evidence of a second, smaller collision. This later impact broke up the original melt sheet into a type of rock known as breccia, where fragments of earlier rocks are fused together by the energy of the impact. Crow explains the structure vividly:
“Breccias are similar to what you would see if you went and chipped out a chunk of concrete. You would see all these little rocks, and then they’re fused together by the cement. But the meteorite is fused together by the impact process. You get all these chunks of different kinds of rocks that the impact hit into. These all get mixed up, and then it gets fused together like your concrete sidewalk.”
Breccias offer a direct record of how successive impacts modify a planetary surface, providing clues not just about collisions but about the sequence and intensity of ancient cosmic events.
A Third Collision Sends the Meteorite to Earth
The final stage of NWA 12593’s journey occurred much later. A subsequent impact launched the meteorite off the moon, sending it on a collision course with Earth. This third event allows scientists to study lunar geology without setting foot on the moon itself, offering a tangible link between planetary surfaces across the solar system.
Crow emphasizes the rarity of these aligned records: “It’s not very common, which is why we’re very excited about it. It’s pretty rare to have all three records line up like this.” By correlating lunar impacts with those on Earth and asteroid 4 Vesta, the study provides a unique window into the early solar system’s transition from constant collisions to more sporadic events following planetary formation.
