Were the Engineers banished.

It's not a plot or direction I'd hope for to be honest. Perhaps this tie between all these races implied in the recent trailer, was symbolic of a war or conflict with a similar foe. We are assuming these historical / archeological pictures are all from earth but what if earth is only one planet that this evidence has been found, and some of the other civilization ties are from discoveries of other planets. Earth just happens to be the only planet that is still alive. Either the SJ engineer race was purposely burried and entombed for a reason, or destroyed itself before it unleashed its plans on earth. This, along with the SJ trying to destroy earth seems so contrived and ordinary to me.