National Geographic relays a spectacular find in the African Sahara desert: a single graveyard covering two different cultural periods spanning 5000 years near the shores of a now vanished lake.
"The scientists eventually uncovered 200 burials of two vastly different cultures that span five thousand years—the first time such a site has been found at a single site. Called Gobero, the area is a uniquely preserved record of human habitation and burials from the Kiffian (7700 to 6200 B.C.) and the Tenerian (5200 to 2500 B.C.) cultures."
What I find interesting is the research team wasn't in the area looking for human artifacts or remains, but instead was a team of paleontologists looking for dinosaur bones.
The area was a lush grassland during the period of habitation, which gave way to desertification over the historical period and the rains which supported the vegatation withered. The Kiffian culture was previously known to be in the area from artifacts but human remains from the period were exteremly rare if not unknown. This early period appears to have been better able to support human settlement. After an intervening dry spell, the Tenerian culture arrived in the area, making adaptations to exist in the drier climate but eventually forced to move on as the climate continued to shift.