Spaw is absolutely correct: the development of life elsewhere probably did NOT follow the same path as on Earth. For example, silicon/oxygen instead of carbon/oxygen is possible, the problem being the excretion of SiO2, a solid we call "sand", instead of CO2, a gas; this is not insuperable however. There are other possibilities as well: fluorine, chlorine, and other reactive gases plus a solid (although I wouldn't want to visit with a fluorine-based life form!).

We conceive of "aliens" in our own image, man or "monster". They may be completely beyond anything we can conceive, just as we may be beyond their conception.

I've long thought it would be interesting if all intelligence evolved at roughly the same rate and achieved space flight at roughly the same time....