Tonight on Comet (network) they showed the Stargate: SG-1 episode "Crystal Skull". If you stare into the eyes of the skull, you see the aliens. Daniel's grandfather had found a crystal skull 20 years ago and saw the aliens, but the Mayan temple collapsed after he returned to earth.

This reminded me a little too much of Indiana Jones and the Kingdom of the Crystal Skull, so I checked on the dates. The Stargate episode was first "broadcast" (on Showtime) on March 3, 2000. Indiana Jones was released (in the US) on May 22, 2008.

They are different enough that I don't think that there are any copyright problems, but claims have been made on less. Besides, would you want to claim that IJ&KoCS was copying your idea?

Crystal skulls are a real thing, and there has been a lot of questions about how they were created. It only makes sense that numerous storytellers would come up with the idea that they were made by aliens.

TG