Cosmology

The most common explanation for the formation of planet Earth is that it formed by gravitational collapse from a cloud of particles (gas, ice, dust) swirling around the Sun.  Specifically, the idea is that small planetesimals form as the various particles clump together (perhaps initially by cohesion, then by gravity), eventually growing into planets.  Known as the “accretion hypothesis,” this is the standard model of planet formation, not just for Earth, but for nearly all planets.* Significant debate continues regarding the formation of the Moon, but the most widely-held hypothesis is that the Moon formed in a similar way via accretion of impact material produced by a violent collision between a Mars-sized object and the Earth. For purposes of the Read More ›