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The exact origin of our planet's water, which covers about 70 percent of Earth's surface, is still a mystery to scientists. Many researchers think that, instead of water forming at the same time as Earth, objects in the outer solar system delivered water to Earth in violent collisions shortly after its formation.

Researchers speculate that any water gathered on the surface of the planet as it formed 4.5 billion years ago would have most likely been evaporated away by the young, blazing sun. That means that water probably came here from somewhere else. The inner planets (Mars, Mercury, Venus), were also probably too hot to house water during the solar system's formation, so our water didn't come from them.