Scientists discover unlikely cosmic origins of Earth's water

Some 4.5 billion years ago, the swirl of gas and dust around the Sun formed planet Earth.

In the beginning, our planet was dry.

The bodies of flowing water that make Earth unique amongst other planets in the Solar System had not yet formed. And till today, scientists aren't exactly sure how water got to planet Earth in the first place.

A new study aims to resolve this longstanding mystery by looking at the composition of meteorites. The results suggest these rocky visitors may have carried water along with them on their journey to Earth.

The study was published Thursday in the journal Science.

According to models of the Solar System, the Earth should be a dry planet, which means it would have likely been devoid of life. But the presence of oceans and seas — and life — has left scientists questioning where this water originated.

Previous research suggested water was delivered to the Earth by way of the asteroids and meteorites that crashed into the planet during its early, chaotic history. But other theories suggested the water was her all along, hidden in the very rocks that formed the planet.

The team of researchers behind the new study looked at samples of enstatite chondrite meteorites, a rare form of meteorite believed to have been forged from the nebula that birthed the Solar System.

These space rocks were exposed to the heat and radiation of the young Sun during their formation, so scientists theorized they would be too dry to deliver the water on Earth. Instead, astronomers assumed water came to Earth later, after its formation, through carbonaceous chondrite meteorites, which came from the outer Solar System.

To try and put the matter to rest, the researchers behind the new study measured the amount of hydrogen in thirteen samples of enstatite chondrite meteorites. Their analysis revealed these meteorites carry a lot more hydrogen than previously believed.

Based on this discovery, these ancient meteorites could have delivered enough hydrogen to the growing proto-Earth to account for at least three times the amount of water in Earth’s present-day oceans, the study authors argue.

Earth's water may have come from the very space rocks that formed the planet.

Abstract: The origin of Earth’s water remains unknown. Enstatite chondrite (EC) meteorites have similar isotopic composition to terrestrial rocks and thus may be representative of the material that formed Earth. ECs are presumed to be devoid of water because they formed in the inner Solar System. Earth’s water is therefore generally attributed to the late addition of a small fraction of hydrated materials, such as carbonaceous chondrite meteorites, which originated in the outer Solar System where water was more abundant. We show that EC meteorites contain sufficient hydrogen to have delivered to Earth at least three times the mass of water in its oceans. EC hydrogen and nitrogen isotopic compositions match those of Earth’s mantle, so EC-like asteroids might have contributed these volatile elements to Earth’s crust and mantle.