Evrim Yazgin
Cosmos science journalist
Water is critical to life on our planet, but the conventional theory of how it ended up being so abundant on Earth might be completely wrong.
The most popular theory is that water made its way to Earth from asteroids bombarding the surface of our planet for about 100 million years when it was very young. Many asteroids are known to have water within them, so this seems a viable option.
Another alternative is that the ingredients for water – hydrogen and oxygen – existed in enough abundance on young Earth already.
The new research, published in the planetary science journal Icarus, details an analysis of a type of meteorite which is very similar in its make up to early Earth about 4.55 billion years ago.
Enstatite chondrites are a rare type of meteorite. Only about 200 are known – about 2% of the chondrite-type meteorites that have fallen to Earth.
The meteorite analysed in this study, LAR 12252, was discovered in Antarctica in 2012. It is 147.5g.
LAR 12252 was analysed using X-Ray Absorption Near Edge Structure (XANES) spectroscopy at the Diamond Light Source synchrotron at Harwell, Oxfordshire in the UK. This method scatters x-rays off a sample to work out what elements are within it.
An earlier study had found trace amounts of hydrogen in organic materials and non-crystalline particles within the meteorite.
The new study showed that significant amounts of additional hydrogen were to be found on sulphur-based compounds. The meteorite is rich in hydrogen sulphide – about 5 times higher than what the previous study had found in the non-crystalline sections.
Contaminated parts of the meteorite showed little to no hydrogen, meaning the hydrogen-rich compounds were present in the meteorite before it crashed to Earth.
The authors say that, because proto-Earth was made of a similar material to enstatite chondrites, it would have had enough hydrogen to explain the abundance of water on our planet.
“We were incredibly excited when the analysis told us the sample contained hydrogen sulphide – just not where we expected,” says study lead Tom Barrett, a PhD student at the University of Oxford. “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.”
“A fundamental question for planetary scientists is how Earth came to look like it does today,” adds co-author James Bryson, also at 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. 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.”
