Mars may have had an oxygen-rich atmosphere 4,000 million years ago, Oxford University academics believe.
This would have been well before the rise of atmospheric oxygen on Earth 2,500 years ago.
The scientists investigated the composition of Martian meteorites found on Earth and data from Nasa’s Spirit rover which examined surface rocks on Mars.
They found that the surface rocks are five times richer in nickel than the meteorites, which led them to their conclusion.
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