The crater formed when an asteroid or comet hit Mars in its early history, about 3.5 to 3.8 billion years ago. The impactor punched a hole in the terrain, and the subsequent explosion ejected rocks and soil that landed around the crater. Layering in the central mound (Aeolis Mons) suggests it is the surviving remnant of an extensive sequence of deposits. Some scientists believe the crater filled in with sediments and, over time, the relentless Martian winds carved Aeolis Mons, which today rises about above the floor of Gale—three times higher than the Grand Canyon is deep.