Earth Had Water Long Before Catastrophic Moon-Forming Collision, Study Suggests

The history of lakes and oceans on Earth is highly speculative. We know they have been around for quite a while, but the exact origin of water has never been confirmed. Perhaps, the most common explanation is the one involving comets and asteroids, space rocks that crashed onto our world bringing water in the process.

Many believe the impacts happened after our planet’s catastrophic collision with another massive celestial body, nearly as big as Mars, some four and a half billion years ago. This crash, dubbed The Giant Impact, was so energetic it threw our moon into existence and started the cycle of life as we know it.

However, there might be a small twist in the story. According to a new study, water might have been present on Earth much earlier than any of us thought, even before the moon-forming collision.

Richard Greenwood from the Open University and his colleagues posited this idea after analyzing and comparing lunar rocks with rocks from Earth.

“We compared the oxygen composition of lunar rocks brought back from all six of the NASA Apollo landings on the Moon with volcanic basalt collected from all of the deep oceans on Earth to help us understand how the Moon formed,” Greenwood, who is also the lead author of the study, said in a statement.

Though this appears more like differentiating between chalk and cheese, there is a whole lot of science involved, the researcher noted. Essentially, it’s the quality of liquid water to alter oxygen isotopes in rocks. If water came on Earth after the moon-forming collision, there should be a vast difference of oxygen content in the two samples.

But, the team hardly noticed any difference after analyzing the results, which suggests water might have existed way before The Giant Impact.

“Our research shows that even an event as catastrophic as two planets colliding doesn’t cause all of the water to be dispersed into space,” the researcher added. “The water stayed in the mix of debris, which gave birth to our planet and its only moon.”

The theory of water-delivering asteroids wasn't taken completely off the table either. The group found most of the water was present on Earth before the collision, but about 5-30 percent was carried by asteroid and comet impacts, New Scientist reported.

That said, knowing more about the chaotic past of water on Earth could help astronomers find exoplanets that may have necessary conditions to host life. If water on Earth can survive a major crash like the one forming the moon, even other planets may also follow the same path. In fact, records suggest, many planets have already undergone collisions like these during the evolution.

“Exoplanets with water on their surfaces may be much more common than we previously thought. And where there is water, there could also be life," Greenwood concluded.

The results of the comparison have been detailed in a paper published in journal Science Advances.