The Earth has been around for 4.55 billion years, a decently long time. You might expect we’d have lots of rocks lying around that are very nearly that old, but in fact they’re hard to find. The Earth is active, with erosion destroying old material, stuff getting subducted down into the deep crust or mantle, and new land created by volcanoes burying older material. In fact, finding truly ancient (say, more than four-billion-year-old) rocks is tough.
But maybe we’ve been looking in the wrong place. A team of planetary scientists with the Center for Lunar Science and Exploration (CLSE) has just announced they found an extremely old Earth rock on the Moon.
Yeah, I know. But it makes sense.