Proof (With picture) : [url]http://www.chronicle.su/news/curiosity-rover-finds-fossil-evidence-of-life-on-mars/[/url]
Not little green men, but a fossilized coral reef, which may or may not even be fossilized yet.
Was discovered when Curiosity found evidence of a once waist-deep streamline.
[Edited on 10.09.2012 10:18 AM PDT]
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[url=http://marsmobile.jpl.nasa.gov/msl/news/whatsnew/index.cfm?FuseAction=ShowNews&NewsID=1372]Might be benign plastic:[/url]