well, regarding the ancient structures in meso& south america
it doesnt always follow that settling an area first means monumental construction or civilization has to occur there as well. I think that may have more to do with geo-graphical factors. SUch as warmer climate, abundance of food etc.

at least one mystery was solved in the past few days, they found remains of St. Exupery's plane which disappeared 60 years ago off Marseilles. (the Little Prince author)