Water did not come to Earth from asteroids, Oxford study suggests

Telegraph

15-04-2025

Water did not come to Earth from asteroids – it was already here, a new study by the University of Oxford suggests.
Many scientists believe that life began on Earth following bombardment by asteroids or comets containing life-giving ingredients including hydrogen which reacted with oxygen to form water.
But Oxford scientists have used ultra-powerful x-rays to peer inside space rocks, which date from the same time as the formation of the Earth around 4.5 billion years ago.
The rocks represent leftover material from when the planets were forming in the Solar System, and so offer a snapshot of what the early Earth looked like.
The research showed a significant amount of hydrogen sulphide, which was part of the asteroid itself rather than later contamination from falling on to the planet.
Dr James Bryson, an associate professor at the Department of Earth Sciences, said: 'A fundamental question for planetary scientists is how Earth came to look like it does today.
'We now think that the material that built our planet – which we can study using these rare meteorites – was far richer in hydrogen than we thought previously. This finding supports the idea that the formation of water on Earth was a natural process, rather than a fluke of hydrated asteroids bombarding our planet after it formed.'
It has been suggested that water was created in the early Earth when hydrogen dissolved into the magma oceans, where it reacted with oxygen-containing compounds, forming water.
The team looked at a rare type of meteorite known as an enstatite chondrite, which was found in Antarctica, and has a composition like that of the early Earth.
A previous study led by a French team had originally identified traces of hydrogen within the meteorite but it was not known if it had acquired them after crashing to Earth.
'Vital evidence' to support native water theory
But the new research found that in places in the asteroid that showed signs of cracks in the rusting, there was little or no hydrogen present. All the hydrogen was locked deep within the asteroid, forming an intrinsic part of its makeup.
Tom Barrett, a doctoral student in the Department of Earth Sciences, who led the study, said: 'We were incredibly excited when the analysis told us the sample contained hydrogen sulphide – just not where we expected.
'Because the likelihood of this hydrogen sulphide originating from terrestrial contamination is very low, this research provides vital evidence to support the theory that water on Earth is native – that it is a natural outcome of what our planet is made of.'
In 2022, a meteorite that fell on a driveway in Gloucestershire was found to contain water that resembles water on Earth. It was the best evidence yet that asteroids delivered water to the planet.
But the new study suggests that by the time the early Earth had become large enough to be struck by asteroids, it would have already amassed enough reserves of hydrogen to explain Earth's present-day water abundance. It suggests habitable conditions do not rely on space rocks and could have implications for searching for life on other planets.
The research was published in the journal Icarus.