Supposing there's a 1955 Cadillac Series 62 Coupe in the middle of Antartica, which most likely there isn't, it didn't fall there from space.

I have no particular stakes on this discussion besides this one, I just dropped by to say this: I don't see any problem with the construction of that statement. At least as an informal or "folk" logic argument.

ok so the question still stands, you dont think theres a car in antartica, but if there is you know it didnt come from space

how do you know either things and why does the first mean the other is not possible?

also your example is using "from space" which is obviously fictional compared to "biological" which there is plenty of evidence for

why else would you write "if it exists" if you already knew a difference existed? you would just say that you dont believe its biological in that case, so it seems like youre trying to go backwards and deny your own words here