BT,
There is a very simple explaination for a rare mineral being on earth, which is also the same for the artifact being on earth.
We didn't know about it.
Hence why we never paid any attention to it.
Uranium has been around for centuries, but only in the past 5 decades has there been a desire to dig it up and use it.
If we don't have a use for a rare mineral, chances are we don't care about it. There's tons of rare minerals on earth that we know of, but don't use and hence don't mine. But the moment someone found a use for it, we'd be digging it up like crazy.
The PSX game C-12, aliens were mining earth for Carbon, the people included.
Its a simple explanation for a variety of scenarios. Something is on earth, we don't know about it, but the aliens do. Let the conflict begin.
