[Science and the world of tomorrow] Life carried to Earth by a meteor or comet, would we even know if it did?

I was at one of the Brethren’s home watching the science channels he frequently watches and it was speaking on the Apollo missions and how they were worried about bringing some space virus back with the samples they collected. What got me thinking is on past threads here, some said that we could not be affected by a virus from space unless it had the same DNA make up as us or something like that. It serves good reason to me that if any life out there evolved or developed from some other path than humans, which life might not look like any life to us in reality. What if that life to us as just a chemical process? Say a meteor lands with extraterrestrial life but that life was not based off what we could recognize, say that life appeared as corrosion on metal, that as it reproduced on the metal the metal got brittle and lost its integrity, would we just see it as some molecular contamination and miss it as a life form altogether?