In a study published in Science, researchers present new evidence that Earth has had its water since the very beginning, and did not arrive via asteroid as previously thought. Using samples of volcanic rocks taken from the arctic Baffin Island in 1985, which have largely remained untouched since the Earth's formation, scientist have found evidence of water deposits. This evidence comes in the form of deuterium, a modified form of hydrogen that creates what we call "heavy water." This is the same unique signature found in asteroids and comets, thought to carry water. In this case, however, the scientists found water that was very poor in deuterium. According to Lydia Hallis, a researcher at the University of Glasgow, this makes it more likely that Earth's water came from the dust that formed our solar system's planets.

As reported in the Washington Post on November 13, 2015.