Enjoyed a drink of water today? You've the Moon to thank. And without it, we might not exist

Our blue-green planet didn’t used to be so blue. And without the blue, there would be no green either.

But how Earth acquired and retained the water that allows life to exist has long been debated.

As with the other inner planets of the Solar System, the forming Earth is thought to have been stripped of volatile elements like hydrogen, helium and water by the Sun’s heat. So how did we get them? 

While the prevailing theory is that they arrived via meteorite bombardment, a study from the University of Bern in Switzerland suggests Earth’s water came from a collision between the proto-Earth and another planet.

This planet, called Theia, smashed deep into the early Earth, delivering water and also ejecting a huge chunk that became the Moon.

This could also help explain why life is so rare in our Solar System – the young Earth was the only planet to get hit.

The team used isotope and element data from meteorites and rocks, and the decay of manganese-53, to model when Earth’s chemistry changed. 

"Thanks to our results, we know that the proto-Earth was initially a dry rocky planet," explains lead author Pascal Kruttasch.

"It can therefore be assumed that it was only the collision with Theia that brought volatile elements to Earth and ultimately made life possible there."

Co-author Klaus Mezger adds: "Earth does not owe its current life-friendliness to a continuous development, but probably to a chance event – the late impact of a foreign, water-rich body."