The Long Duration Exposure Facility (LDEF), a NASA research satellite launched in the 1980s, showed that bacterial spores remain viable in space for at *least* 6 years (after 6 years, the satellite was retrieved).
It should be mentioned that very, very few bacteria sporulate. *Bacillus*, *Clostridium*, and not much else. AFAIK magnetotactic bacteria don't sporulate.
Anyway, I guess the meteorite was settled by bacteria after it had arrived in Antarctica...