Mars' Atmosphere Boasted Oxygen Long Before Earth's: A Study

Mars once boasted an atmosphere drenched in oxygen.

This was the conclusion researchers at Oxford University came to after studying differences between Martian meteorites and rocks examined by NASA's rover Spirit - differences, they say, that would be explained should there have been high amounts of oxygen roughly 4,000 million years ago.

If correct, this means Mars' atmosphere hosted oxygen a full 1,500 million years before Earth's.

Specifically, the scientists analyzed the compositions of Martian meteorites found on Earth and data from Spirit taken from the surface of rocks in the Gusev crater on the Red Planet. In doing so, they found that the latter were five times richer in nickel than the meteorites.

This initially puzzled the researchers and cast doubt on whether the meteorites were typical volcanic products from Mars.

However, upon further analysis, they came to a different conclusion.

"What we have shown is that both meteorites and surface volcanic rocks are consistent with similar origins in the deep interior of Mars but that the surface rocks come from a more oxygen-rich environment, probably caused by recycling of oxygen-rich materials into the interior," said Professor Bernard Wood, of Oxford University's Department of Earth Sciences, who led the research reported in this week's Nature.

The result, Wood explained, is surprising given that, while the meteorites are geologically young at just 180 million to 1,400 million years old, the rover was analyzing a very old part of Mars as the time, estimated at some 3,700 million years old.

While it's still possible that the geological composition of Mars varies significantly from region to region, the researchers believe that the more likely reason for the differences is through a process known as subduction, in which material is recycled into the interior.

Ultimately, they suggest that the Martian surface was oxidized very early in the history of the planet and that, through subduction, this oxygen-rich material was drawn into the shallow interior and recycled back to the surface during eruptions 4,000 million years ago.

The meteorites, on the other hand, are much younger volcanic rocks that emerged from deeper within the planet, leaving them less influenced by this process.

"The implication is that Mars had an oxygen-rich atmosphere at a time, about 4000 million years ago, well before the rise of atmospheric oxygen on earth around 2500 million years ago," Woods surmised. "As oxidation is what gives Mars its distinctive color, it is likely that the 'red planet' was wet, warm and rusty billions of years before Earth's atmosphere became oxygen rich."