Boulder, Colo., USA: The first few billion years of Earth’s history saw the rise of life, the atmosphere, and the oceans. Still, that time is shrouded in mystery: not many rocks remain that preserve a record of those early iterations of our modern world. Dynamic geologic processes like erosion, subduction, and burial mean the surface is constantly being reshaped, and older rocks aren’t very common. But that time period is critical to understanding our own origins and how catastrophic events like asteroid impacts might have affected early life on the planet.
“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?” says Carolyn Crow , a planetary scientist at the University of Colorado Boulder. “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.”
To learn about Earth’s earliest years, geologists often turn to samples that originated from the Moon, which doesn’t have active geologic processes but still shares a common impact history with us. Now, a new study in Geology has discovered evidence of a major impact event about 3.5 billion years ago on the Moon, matching the ages of known impacts on Earth and in the asteroid belt and helping scientists to connect the history of the inner solar system.
The scientists studied a lunar meteorite found in northwest Africa (NWA), called NWA 12593. In it, they found evidence of three different impact events. The first, which radiometric dating reveals occurred about 3.5 billion years ago, was massive—large enough to turn the surface of the moon into a sheet of molten material resembling a lava flow and generate a mineral called cubic zirconia that only forms at super-high temperatures. Cubic zirconia is commonly manufactured for jewelry, but when the mineral’s cooling isn’t highly controlled in a lab, it doesn’t survive to low temperatures found on the surface of Earth or the moon. However, Crow and the team were able to discern traces of the mineral, called cubic zirconia phase heritage, in their samples.
The second impact event was recorded by the meteorite itself. It’s a type of rock called a breccia, which formed after a smaller impact that broke up the melt sheet of the first impact.
“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 it's fused together by the cement,” says Crow. “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.”
The evidence of the third impact is the meteorite’s presence on Earth. A more recent collision must have knocked the chunk of breccia off the moon and on a course toward Earth.
The timing of the first big impact recorded in NWA 12593 lines up with known impacts on Earth and 4 Vesta, the fourth largest asteroid in the asteroid belt. Finding similarly aged impact events recorded on three celestial bodies is uncommon and the new discovery provides a key link at a time when the solar system was transitioning from constant collisions during planet formation to more sporadic impacts from the breakup of asteroids.
“It's not very common, which is why we're very excited about it,” says Crow. “It's pretty rare to have all three records line up like this.”
CITATION: Crow, C., et al., 2026, Three-body evidence of ca. 3.7 Ga to 3.2 Ga bombardment across the inner solar system: Geology, 12 May 2026, https://doi.org/10.1130/G54386.1
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Geology
Three-body evidence of ca. 3.7 Ga to 3.2 Ga bombardment across the inner solar system
12-May-2026