Huuh.. that's the most interesting question of the day, lol o:
Needed... needed... wwhat is neede?.. :l I'd say a proper temperature which stays in the acceptable range.. the right materials (water etc, most other ones can be replaced though.. see that bacterium with arsenic instead of phosphor in the DNA!).. probably a form of atmosphere (to have a pressure).. and much luck!
Luck because there has to be a source of the "life" evolution. Some way there must have happened that static materials combined themselves by hazard so that a very, very primitive form of "life" got created which got the ability to survive and even to change it's form: evolution..

Air

anything and everything god makes for them :)

truth is i think scientist are stupid to look for planets like earth life might be on planets nothing like earth instead life evovled diffrently