According to TechnoBuffalo.com, about 4 billion years ago Mars had a oxygen rich atmosphere. The meteorites found on Earth, which bounce back from the Red Planet, and the Spirit Rover studies have shown that the rich amount of Oxygen was present in the atmosphere.
Professor Benard Wood said :
“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 came from a more oxygen-rich environment, probably caused by recycling of oxygen rich materials into the interior”.
The NASA Mars Rover Spirit has possibly analyzed is most likely 3.7 billion years old and the bouncing back meteorites are around 1.4 billion years old.
The variation in geological composition of Mars is because of the subduction process. In this process, the rock gets drawn into a shallow region and then shot back up through volcanic process, recycling of rocks on Mars.
Professor Wood also said that if the Red Planet indeed had an oxygen rich atmosphere, the planet would have been wet, warm and rusty because of its oxidation.
Image Source: Allthingsd.com