The Moon’s Catastrophic Birth
The extremely similar chemical composition of rocks on the Earth and moon helped scientists determine that a head-on collision, not a glancing blow, took place between Earth and Theia. Copyright William K. Hartmann
The more we learn about the early solar system, the more chaotic those times seem. It was a busy time. Newborn planets were jostling around, some of them were migrating outwards, and others — such as Earth — were ground zero for ongoing collisions and impacts. One of those collisions formed the Moon. For a long time, planetary scientists cited the glancing blow by a planetary embryo called Theia as the event that made the Moon. But, it turns out that the collision was more of a head-on smack-up than they suspected. Instead of sideswiping Earth at a 45-degree angle, Theia hit Earth squarely in the gizzards.
Analysis of a Head-on Collision
The clues that helped scientists figure out the details of this collision after the fact lies locked away in rocks from both Earth and the Moon. You analyze the chemical compositions of rocks to find out their formation history and subsequent erosion or bombardment. The Apollo missions brought back Moon ...