Third Pod From The Sun

About 11,000 years ago, the Sahara desert turned green. The region received ten times the rain that falls there now, filling lakes and supporting savannahs, woodlands, and human communities. This was not the first time our species had encountered a green Sahara. Every 20,000 years or so, the wobble in Earth’s axis called precession brings the northern hemisphere a little closer to the Sun in summer, and more rain to the Sahara. The wet period ended abruptly, 5,000 years ago, leaving rock art and artifacts in the sand. But the people were not gone, they had just moved. As the sands took back the Sahara, people congregated along the Nile valley, and the Egyptian civilizations arose. Our guest Jessica Tierney is interested in how climate changes influence human migrations. Tierney is a paleoclimatologist at the University of Arizona in Tucson where she studies past climate change, from the time of the dinosaurs, to the human diaspora 60,000 years ago, to more modern shifts in North America’s own Southwest monso