Explorer and scientist Paul Sereno made an extraordinary discovery in the middle of the Sahara desert: While prospecting for dinosaur bones, he stumbled across an ancient human cemetery more than 5,000 years older than the Egyptian pyramids. Who were these people and what were they doing in the middle of the desert? How did they live and die? What can this mystery tell US about our planet? And why are there two distinct groups of people here, existing thousands of years apart?