New evidence challenges theories of origin of water on Earth, study suggests
Scientists from the University of Oxford analyzed a rare type of meteorite known as an enstatite chondrite. The space rock dates to around 4.6 billion years ago and is believed to be similar in composition to early Earth, according to a study published Wednesday in the journal Icarus.
The researchers found that the majority of the hydrogen contained within the meteorite was intrinsic, rather than being present due to contamination, suggesting that early Earth would have been home to sufficient hydrogen to have allowed the formation of water molecules.
This finding calls into question the widely held belief that hydrogen arrived on Earth in asteroids that bombarded what was previously a dry, rocky planet incapable of supporting life.
'We assumed that Earth has water today because of quite a lucky scenario where it had been hit by these asteroids,' lead study author Tom Barrett, a doctoral student in the department of Earth sciences at the University of Oxford, told CNN on Wednesday.
'But what we've demonstrated in this study is that actually the material which formed Earth in the first instance actually did contain a lot of hydrogen and oxygen,' he added. 'The discovery of hydrogen in this meteorite means that Earth potentially could have been hydrated or wet from its initial formation.'
As for why the levels of hydrogen identified in the study previously hadn't been detected, Barrett explained the chemical element is hard to measure, particularly at such low concentrations. The detection was only possible thanks to a technique known as X-ray Absorption Near Edge Structure, or XANES, spectroscopy, he said.
'To do that you need a particle accelerator,' he said. 'This is like an enormous, really expensive facility, which we've been very fortunate to have used to this study. But it's not exactly the kind of experiment that you can do in the garage.'
The study potentially upends our understanding of early Earth, but the discovery of hydrogen in the meteorite doesn't mean that life would have necessarily evolved sooner, Barrett said. This is because the habitability of a planet may depend more on the way it evolves than the material it is formed from, he said.
A team of scientists at the French National Centre for Scientific Research had previously analyzed the meteorite, known as LAR 12252, which had been collected in Antarctica. The August 2020 study found that the space rock's chondrules, or minuscule spherical objects, and organic material contained within it had traces of hydrogen. The research, however, only accounted for a portion of the hydrogen within the meteorite.
The researchers behind the new study believed more hydrogen could be attached to sulphur within the meteorite. The team unexpectedly detected hydrogen sulphide within the fine matrix immediately surrounding the chondrules — 'on average almost 10 times more' hydrogen sulphide than found in the spherical objects, according to the study.
'We were incredibly excited when the analysis told us the sample contained hydrogen sulphide — just not where we expected!' Barrett said in a statement. '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.'
Next, Barrett plans to analyze more meteorites in an effort to ascertain exactly how much hydrogen would have been present on Earth, and how much may have been delivered from external sources.
Working out how Earth came to look the way it does today is a fundamental question for planetary scientists, said study coauthor James Bryson, an associate professor in the department of Earth sciences at the University of Oxford.
'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,' he said.
'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.'
Matt Genge, a planetary scientist at Imperial College London, who was not involved in the study, told CNN that while the study is an 'interesting result,' the evidence is not sufficient to overturn the longstanding theory of the origins of water.
The meteorite in question had been in Antarctica likely for hundreds of thousands of years, he said, and it is impossible to completely rule out the chance that the hydrogen may have formed during that time.
'Just the fact that there is a possibility makes the argument less strong,' Genge said.
Bryson acknowledged that the meteorite was indeed likely on Earth for many years before it was collected but stands by the study results.
'We believe we have taken every effort we can in our analysis workflow to mitigate the impact of terrestrial water on our results, and we do think that some of the total amount of H (hydrogen) in the meteorite is due to Earth's water (maybe about 15%),' Bryson said via email in response to Genge's statement.
'We also think that some H (hydrogen) was still delivered from asteroids and comets, however we now think this is a small proportion of the total H (hydrogen) found throughout our planet. So Matt's assessment of this meteorite is justified, but we strived to minimise his concern.'
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