Scientists now know that liquid surface water was present on Earth before the planetary "giant impact" that created the Moon.
It used to be thought that most, if not all, ocean water would later be carried to Earth. Asteroid and comet fire
The fact that liquid water can survive catastrophic planetary effects means that it is abundant in other star systems should be.
The Presence of Liquefied Surface Water in the Form of Lakes and Oceans (19659003) Scientists compared the oxygen composition of lunar rocks returned by Apollo astronauts with the Earth and that of volcanic rock from the seafloor.
They found only a small difference between the lunar and earth rocks. If most of the water on Earth had arrived after the giant impact, the rocks would have distinctly different oxygen compositions.
The findings suggest that liquid water must have existed on Earth before its moon-forming collision with a Mars planet
Scientists know that many exoplanets in other star systems experienced similar high-energy collisions at the beginning of their evolution.
The lead researcher Richard Greenwood of the Open University said: "Exoplanets with water on their surfaces can make up much more than we previously thought, and where water is, there could be life."