Where Did Earth’s Water Come From?

Water makes up around 70 per cent of the earth’s surface, with over 326 million trillion gallons to be found here – but the answer to the question of where did it all come from has remained something of a mystery over the years… until now.

New research from the University of Glasgow looking into the origins of the water on earth has just uncovered new evidence that it may, in fact, have come from the sun.

Published in the Nature Astronomy journal, the study analysed an ancient asteroid and found that extraterrestrial dust grains carried water to earth as the planet formed. The water in these dust grains was produced by space weathering, where solar wind (charged particles from the sun) alters the chemical composition to produce water molecules.

Scientists have spent decades puzzling over the source of the earth’s oceans, with one theory suggesting that C-type asteroids (a water-carrying space rock) could potentially have brought water to the planet 4.6 billion years ago, when it was in the final stages of its formation.

But this study saw the team use a cutting-edge analytical process known as atom probe tomography, scrutinising samples from an S-type asteroid, a different type of space rock that orbits closer to the sun than C-types.

The atomic structure of the grains were measured one atom at a time to detect individual water molecules. It was found that a significant amount of water was produced just below the surface of dust-sized grains by space weathering.

The early solar system was apparently incredibly dusty, so there was a lot of opportunity for water to be produced in dust particles. This would then have rained down onto the early earth, along with C-type asteroids, to help build the oceans that we know today.

Lead author of the study Dr Luke Daly said: “Crucially, this solar wind-derived water produced by the early solar system is isotopically light. That strongly suggests that fine-grained dust, buffeted by the solar wind and drawn into the forming earth billions of years ago, could be the source of the missing reservoir of the planet’s water.”

Earth is one of the most unusual planets in the solar system because it has liquid water on its surface – which is rare. Although water is relatively common throughout the universe, it’s typically found in the form of ice or water vapour, instead of liquid.

Liquid water is only found on the right-sized planets, which also have to be within the Goldilocks Zone (or habitable zone), which is the range of distance with the right temperatures for water to remain a liquid.

So for any planet to have liquid water on its surface is incredibly rare – and for 70 per cent of its surface to be water is practically unheard of… making earth one of the most intriguing planets of them all!

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