for a while, people thought earth’s water did not come from the planet’s region of the protoplanetary disk. instead, it was thought that water and other volatiles must have been delivered to earth from the outer solar system later in its history. but hydrogen inside the earth did play some role in the formation of the ocean. the two ideas may each be partly right. water was delivered to earth by impacts from icy planetesimals (asteroids) in the outer edges of the asteroid belt. how much is not known.