We typically think of the moon as a static, floating object that has remained the same for basically its entire lifetime, with an occasional asteroid impact serving as an exception. That understanding is grounded in physics—the moon should have cooled rapidly after forming when a huge protoplanet hit the early Earth around 4.5 billion years ago. But some lunar material returned from the Chang'e-5 mission was notably formed only around 2 billion years ago, yet appeared to be volcanic in origin.