Where did water on Earth originate?  Our solar system was formed 5 billion years ago by a supernova (a catastrophic explosion of a star).  This supernova left behind our sun and a cloud of material (including water) called a solar nebula, out of which the planets formed.  Although some of the other planets retained water, it is locked away as ice and useless to life. Earth is the only planet with liquid water.  80% of Earth's surface is covered by oceans, where early life evolved.