According to a study released in the journal Nature, the Martian atmosphere may have been rich in oxygen 3.7 billion years ago. Such a fact would bode well for the continuing argument that the planet supported life at one time.
The study, authored by Bernard Wood of Oxford University, theorizes that the atmosphere of Mars might once have had plenty of oxygen after Wood and his colleagues compared meteorites from the planet to data on surface rocks collected by the Spirit rover. The samples, which share volcanic beginnings, were found to be geochemically different: the surface rocks were more oxygen-rich than the meteorites.
Spirit launched in 2004 with the Opportunity rover and operated until 2010. During that time it collected rock samples from Gusev Crater, a region of Mars estimated to be over 3.7 billion years old. Wood believes these ancient rocks may have come into contact with Mars’s oxygen atmosphere before experiencing subduction, when the rocks would have been recycled in the planet’s interior. The oxygen-rich rocks then reappeared via volcanic eruption some four billion years ago.
The meteor samples, alternatively, are being considered much “younger” than their surface counterparts. At anywhere between 180 million to 1.4 billion years old, these rocks likely came from deeper inside the Red Planet and thus had less contact with any oxygen that was in the atmosphere.
Although the theory is plausible, not everyone is in agreement that the samples are definitive proof that Mars obtained an atmosphere full of oxygen much earlier than Earth. Francis McCubbin of the University of New Mexico spoke with the BBC and stated that he did not reach Wood’s conclusions concerning the samples. He said that the oxidation of the surface could occur without the presence of oxygen gas.
However, he did agree with Wood’s conclusions that there are “substantial redox gradients with depth” on the planet. The process of redox (also known as reduction-oxidation) could potentially support certain types of life that use the reactions for energy and/or as a food source.
Yet Wood expects he is on to something. “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,” he said.
In terms of how Mars would have beaten Earth to an oxygen heavy atmosphere, Wood explained that Mars’s lower gravity allowed for easier loss of hydrogen molecules during photolysis of existing water. This is the process wherein the water vapor of Mars would have broken down into its component elements through the interaction of the atmosphere with radiation from the Sun.
“So the oxygen build-up could be enhanced on Mars relative to Earth,” he said.