We all know the universe is trying to kill us, and some days that seems more apparent than others.

Take the moon for instance. This nice big rock in the sky is thought to have been formed when a Mars-sized object hit a trying-to-become-Earth object. This messy collision led to a splash of a lot of the lighter density materials and the merger of the higher density cores. Our system, with Earth’s thin crust and large core and our oddly low-density moon, is the result. Born out of destruction, the Moon has experienced 4.5 billion years of battering as asteroids, comets, and all manner of objects great and small have continually collided with its surface.

These impacts haven’t just shaped the cratered surface of the moon, they have also impacted what minerals have formed. In a new work from the Royal Ontario Museum, planetary scientists have found evidence of cubic zirconia embedded in a moon rock. This mineral is often used as an alternative to diamonds in jewelry and is formed in hot dense environments that exist either in labs or in the melting outer layers of worlds being impacted. Since jewelry makers aren’t on the moon making these gems, well… we know something horrible happened in the past.

This particular rock was picked up during the Apollo 17 mission in 1972 and was protected for future study. It was hoped that as technology advanced, we’d gain new abilities to learn from these precious rocks. In setting aside these rocks, NASA acknowledged we might not be going back to those places anytime soon, although I’d like to believe they assumed we’d be going back to other places to get other rocks. Today, we do, at least, have better technology. This work, published in a new paper in the journal Nature Astronomy, describes how a team used modern microscopes to scan the minerals. Now, earlier I said they found evidence of cubic zirconia. What they actually found are baddeleyite crystals that formed 4.3 billion years ago from the decay of cubic zirconia that formed in the heat – the 2300 deg C heat of an impact. While we can see craters and get a sense of the forces needed to excavate these large hollows on the moon, these microscopic minerals give us precise temperature limits – it was 2300 deg C or hotter. These rock melting temperatures would have driven mixing of inner and outer layers of lunar crust, producing the complex array of rocks we see today.

One of the reasons we study the moon is so we can get a better understanding of what happened on our own Earth. The mineral record here is much more confusing due to plate tectonics, weather and other effects like volcanoes. As described by lead author Lee White, “Rocks on Earth are constantly being recycled, but the Moon doesn’t exhibit plate tectonics or volcanism, allowing older rocks to be preserved. By studying the Moon, we can better understand the earliest history of our planet. If large, super-heated impacts were creating rocks on the Moon, the same process was probably happening here on Earth”.

So yeah – our world was beat up, too. We’re just better at hiding our scars with a layer of vegetation and erasing them through weather which, after all, can be seen as a form of exfoliation. 

More Information

• Royal Ontario Museum Press Release 
• “Evidence of extensive lunar crust formation in impact melt sheets 4,330 Myr ago,” L.F. White et al., 2020 May 11, Nature Astronomy