Africa's Sahara Desert is the size of the United States, making it the largest desert in the world. It's also the hottest place on the planet. But now an astonishing series of geological discoveries has revealed this searing wasteland hides a dramatically different past. Scientists have unearthed the fossils of whales, freshwater shells and even ancient human settlements. All clues to a story that would alter the course of human evolution and culminate in biggest climate change event of the last 10,000 years.