Winner of the 2002 Phi Beta Kappa Award in Science Mankind has recently come to the shocking realization that our ancestors survived hundreds of abrupt and severe changes to Earth's climate. In this unique travelogue, William H. Calvin takes us around the globe and back in time, showing us how such cycles of cool, crash, and burn provided the impetus for enormous increases in the intelligence and complexity of human beingsand warning us of human activities that could trigger similarly massive shifts in the planet's climate.