Mars had oxygen-rich atmosphere 4000m years ago University of Oxford

Differences between Martian meteorites and rocks examined by a NASA rover can be explained if Mars had an oxygen-rich atmosphere 4000 million years ago – well before the rise of atmospheric oxygen on Earth 2500m years ago.
Scientists from Oxford University investigated the compositions of Martian meteorites found on Earth and data from NASA’s ‘Spirit’ rover that examined surface rocks in the Gusev crater on Mars. 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 of the red planet.