To understand the mantle—the largest layer of Earth’s rocky body—scientists drill deep cores out of the Earth. Scientists drilled the deepest core yet and recovered serpentinized peridotite that forms when saltwater interacts with mantle rock. Although this is the deepest into the mantle scientists have ever drilled, the mission didn’t uncover pristine mantle that lies beyond the Mohorovičić discontinuity, or Moho, boundary. Although this makes this particular drill core the deepest sample of the mantle yet, going that deep into the rock wasn’t the goal of this record-breaking expedition. It also contained rocks known as gabbros, which are coarse-grained igneous rocks.