Study: Ancient Mars Had More Oxygen Than Ancient Earth

Study suggests Mars was once "wet and warm."

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Its air is dusty and suffocating now, but at some point in its history Mars' atmosphere had more oxygen than Earth, according to researchers.

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Mars' atmosphere likely once had more oxygen than Earth's, according to a new study by researchers at Oxford University.

[PHOTOS: NASA's Curiosity Lands on Mars]

By comparing rocks found by NASA's Spirit rover (which got stuck on Mars in 2009 and hasn't communicated with Earth since early 2010) with Martian meteorites that have landed on Earth, Bernard Wood and his team infer that the Red Planet once had "a significant amount of oxygen."

Astronomers have long suspected that Mars once had oxygen in its atmosphere – it gets its name "The Red Planet" because the planet is essentially covered in rust, or iron oxide, which is made up of iron and oxygen. But the rocks studied by Spirit, which are much older than the meteorites that have landed on Earth, contain much more oxygen in them than the meteorites.

"It appears that the 4 billion year old rocks come from a more oxidized environment than the younger meteorites," he says. "Our conclusion is the source of that oxygen most likely has to do with the atmosphere."

[READ: Curiosity Rover Finds Evidence of Ancient Stream on Mars]

In fact, 4 billion years ago, scientists believe Earth's atmosphere contained little to no oxygen. In January, scientists reported finding microbe fossils in Australia that are 3.5 billion years old and predate oxygen on the planet. But until oxygen was plentiful in the atmosphere, life likely didn't thrive on Earth.

"All we can really say for certain is that oxygen existed early on in Mars' history at a time it wasn't being produced on Earth," Wood says.

Mars' current atmosphere is made up of about 95 percent carbon dioxide, 2.7 percent nitrogen, 1.6 percent argon and traces of oxygen, water vapor and several other elements. Wood says that billions of years ago, it was likely a much different place.

"One model for Mars is that early in its history, about 4 billion years ago, it was wet and warm," he says. "It sounds a bit like Florida is today."

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