Some theories have been stated that presume the Earth had no large moons early in the formation of the Solar System, 4.6 billion years ago, Earth being basically rock and lava. Theia, an early protoplanet the size of Mars, hit Earth in such a way that it ejected a considerable amount of material away from Earth. Some proportion of this ejecta escaped into space, but the rest consolidated into a single body in orbit about Earth, creating the Moon.