Mars was Oxygen-rich, Wet, Warm and Rusty Billions of Years Ago

Mars has surprised NASA scientists again and again. Rovers have uncovered evidence of rivers, ice and other features that are more familiar to us on Earth than on an alien planet. Now, the Mars rover Spirit may have uncovered a feature of the Red Planet that's even more surprising. Differences between Martian meteorites and rocks examined by the rover could be explained if the planet had an oxygen-rich atmosphere about 4,000 million years ago--well before the rise of atmospheric oxygen on Earth about 2,500 million years ago.

The samples from Mars were actually taken from the Gusev crater. Five times richer in nickel that the Martian meteorites found on Earth, these space rocks puzzled scientists. In fact, they made researchers doubt whether the meteorites actually were typical volcanic products of the Red Planet.

In order to investigate this a bit further, the researchers took a closer look at the rocks and the meteorites. They found that both the rocks and the meteorites were actually consistent with similar origins in the deep interior of Mars, but that the surface rocks came from a more oxygen-rich environment.

"The result is surprising because while the meteorites are geologically 'young,' around 180 million to 1,400 million years old, the Spirit rover was analyzing a very old part of Mars, more than 3,700 million years old," said Bernard Wood of Oxford University's Department of Earth Sciences in a news release.

Although it's certainly possible that the geological composition of Mars varies immensely from region to region, scientists believe that it's more likely that the differences arise through a process known as subduction. This process doesn't just occur on Mars, though, it also happens on Earth; material is recycled into the interior, essentially giving the planet a "new" crust over millions and millions of years. Essentially, the oxygen-rich material was drawn into the shallow interior and recycled back to the surface during eruptions about 4,000 million years ago. The meteorites, in contrast, are much younger volcanic rocks that emerged from deeper within the planet and so were less influenced by this process.

"The implication is that Mars had an oxygen-rich atmosphere at a time, about 4,000 million years ago, well before the rise of atmospheric oxygen on Earth around 2,500 million years ago," said Wood. "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."

The findings are published in the journal Nature.