Why does mystery = aliens?

Do I know how they're all done? Nope, but thats no reason for me to start making assumptions. None of the "evidence" on the site you listed suggests a non-human source. The most curious piece in my opinion was the metal spheres, but the temperature of the spheres while cooling would burn the plants. Were control samples taken from other sections of the field, and other undisturbed fields nearby? I bet those spheres would be present in the controls, and I bet they're older than the farmer who owns the land.

BTW - from a statistical perspective, I do believe in intelligent life elsewhere; life that could be billions of years ahead of us in terms intellectual development. I *wish* they were here, that would be cool as hell, but I've never been exposed to a quality reason to believe they are.