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...