Rocks on the surface of Mars have yielded the best clue yet that the planet once had an atmosphere rich in oxygen.
Mars owes its sobriquet 鈥渢he Red Planet鈥� to the abundance of iron oxide, otherwise known as rust, on its surface. But in addition to all that iron, NASA鈥檚 Curiosity rover has now found substantial amounts of manganese oxide in rocks in Mars鈥檚 Gale crater.
鈥淲e found 3 per cent of rocks have high manganese oxide content,鈥� of the in Toulouse, France, told the in Vienna, Austria, earlier this week. 鈥淭hat requires abundant water and strongly oxidising conditions, so the atmosphere may have contained much more oxygen than we thought.鈥�
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Mars鈥檚 current atmosphere is 95 per cent carbon dioxide and contains only trace amounts of oxygen. Nevertheless, many researchers have argued that Mars must once have been rich in atmospheric oxygen. This is the most direct evidence to date, the Curiosity team claim.
The rover identified the manganese oxide with the help of its ChemCam, an instrument which zaps rocks with a laser and analyses the resulting dust cloud to identify chemicals and minerals. The researchers haven鈥檛 yet pinned down the exact age of the manganese oxide, but hope to do so with future data from the rover.
Because many of the manganese oxide deposits are close to where a lake once existed in the crater, Cousin says that flowing liquid with dissolved oxygen in it may have played a part in its formation. 鈥淚t鈥檚 a real possibility that there was oxygen in the atmosphere, and possibly water available locally that was oxidising,鈥� she says.
If there was too much oxygen, though, it might not have been a good thing for early life, says Damien Loizeau of the University of Lyon, France. On Earth, oxidation breaks up biological molecules. The appearance of oxygen on Earth was linked to organisms that produced it, but was a disaster for those organisms鈥� neighbours.
鈥淥2 is bad for life as we know it, but we only know life to be able to create large amounts of O2,鈥� he says.
