According to a new study reported in the journal Nature, the atmosphere of Mars could have been rich in oxygen almost 4 billion years ago.

Scientists from Department of Earth Sciences at the University of Oxford analyzed the compositions of Martian meteorites found on Earth and data from NASA’s rovers.

The fact that the surface rocks are five times richer in nickel than the meteorites was puzzling and had cast doubt on whether the meteorites are typical volcanic products.

“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,” explained study senior author Prof Bernard Wood.

“This result is surprising because while the meteorites are geologically young, around 180 million to 1.4 billion years old, the Spirit rover was analyzing a very old part of Mars, more than 3.7 billion years old.”

Whilst it is possible that the geological composition of Mars varies immensely from region to region the team believes that it is more likely that the differences arise through a process known as subduction – in which material is recycled into the interior.

The scientists 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 billion years ago. The meteorites, by contrast, are much younger volcanic rocks that emerged from deeper within the planet and so were less influenced by this process.

“The implication is that Mars had an oxygen-rich atmosphere at a time, about 4 billion years ago, well before the rise of atmospheric oxygen on earth around 2.5 billion years ago. 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,” Prof Wood said.

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Bibliographic information: J. Tuff et al. 2013. Volcanism on Mars controlled by early oxidation of the upper mantle. Nature 498, 342–345; doi: 10.1038/nature12225