Solar System formation
See also: Planetary differentiation The standard model for the formation of the Solar System (including the Earth ) is the solar nebula hypothesis . In this model, the Solar System formed from a large, rotating cloud of interstellar dust and gas called the solar nebula . It was composed of hydrogen and helium created shortly after the Big Bang 13.8 Ga (billion years ago) and heavier elements ejected by supernovae . About 4.5 Ga , the nebula began a contraction that may have been triggered by the shock wave from a nearby supernova .A shock wave would have also made the nebula rotate. As the cloud began to accelerate, its angular momentum , gravity , and inertia flattened it into a protoplanetary disk perpendicular to its axis of rotation. Small perturbations due to collisions and the angular momentum of other...