Mars' atmosphere was "oxygen rich"

Scientists at NASA have discovered using their Spirit Rover that Mars once had an oxygen rich atmosphere 4 billion years ago. This was 1,500 million years prior to the formation of earth. The scientists came to this conclusion because they had analysed samples that the Spirit Rover had collected, they also compared these samples with Martian meteorites that have crashed into earth. The Scientists then were able to examine the composition of the meteorites and the samples collected, they then discovered a high percentage of oxygen. Also  Mars' distinct red colour, shows evidence of a process called oxidation, which obviously as the name suggests needs a high quantity of the oxygen. It is likely that the Red Planet was warm, wet and rusty, billions of years before Earth's atmosphere became oxygen rich, enough for life to develop on Earth. 

This could mean that life did exist on Mars, and it could mean that at some point we could end up living on Mars!