Earth’s Atmosphere Came from Outer Space
The gases which formed the Earth’s atmosphere, and probably its oceans, did not come from inside the Earth but from outer space, according to a study by University of Manchester and University of Houston scientists. The report, published in the journal Science, means that textbook images of ancient Earth with huge volcanoes spewing gas into the atmosphere will have to be rethought. According to the team, the age-old view that volcanoes were the source of the Earth’s earliest atmosphere must be put to rest.
The team of Greg Holland and project director Chris J. Ballentine from the University of Manchester and Martin Cassidy from the University of Houston tested volcanic gases using analytical techniques to uncover the new evidence.
“We found a clear meteorite signature in volcanic gases,” said Holland, the project’s lead scientist. “From that, we now know that the volcanic gases could not have contributed in any significant way to the Earth’s atmosphere. Therefore, the atmosphere and oceans must have come from somewhere else, possibly from a late bombardment of gas and water-rich materials similar to comets. Until now, no one has had instruments capable of looking for these subtle signatures in samples from inside the Earth — but now we can do exactly that.”
The team used an instrument called a multicollector noble gas mass. Multicollection or measuring several isotopes at the same time rather than one after another improves the precision of the measurements. This, coupled with the type of sample the team is using, means they can get higher precision measurements than anyone else — hence they can see these small primitive signatures.
The techniques enabled the team to measure tiny quantities of the unreactive volcanic trace gases Krypton and Xenon, which revealed an isotopic fingerprint matching that of meteorites which is different from that of solar gases.
The study is also the first to establish the precise composition of the Krypton present in the Earth’s mantle.
Ballentine said: “Many people have seen artist’s impressions of the primordial Earth with huge volcanoes in the background spewing gas to form the atmosphere. We will now have to redraw this picture.”
The research was funded by Natural Environment Research Council (NERC).