spacetoday.net: Scientists speculate Mars had early oxygen-rich atmosphere

Posted: Thu, Jun 20, 2013, 7:27 AM ET (1127 GMT)
Differences between rocks on the Martian surface and some meteorites on Earth that came from Mars can be explained if the planet had an oxygen-rich atmosphere early in its history, British scientists reported this week. Scientists had been puzzled by the fact that rocks in Gusev Crater on Mars, analyzed by NASA's Spirit rover, had five times the nickel content as Martian meteorites. Researchers believe that the Gusev Crater rocks are very old, and subject to oxidation processes, whereas the meteorites are relatively young and did not encounter the same processes. The scientists believe this is evidence that the early Martian atmosphere contained significant amounts of oxygen, produced by biological or chemical processes.