Learn how scientists used the fossils of one-celled aquatic organisms, called diatoms, to understand ancient climate conditions in eastern Africa, in this video from NOVA: Becoming Human. White layers of a rock formation consist of deep-water diatoms and darker layers consist of shallow-water diatoms; the scientists interpreted the alternating layers in the formation to mean that a massive lake appeared and disappeared many times in their study area. If this part of Africa indeed experienced wet and dry periods over time, this supports a new idea that suggests climatic variability may have shaped human evolution.

This video is available in both English and Spanish audio, along with corresponding closed captions.