Phew, I'm glad you threw in that last sentence! The largest assumption you made is that biological life evolves the same on every earth-like planet...and that

Phew, I'm glad you threw in that last sentence! The largest assumption you made is that biological life evolves the same on every earth-like planet...and that all life from those planets fits our definition of biological. One of the things I love about good sci-fi is that it challenges these assumptions. I'll throw one out there as an example many would know: the crystalline entity in Star Trek TNG.