Within the geological science of paleoclimatology, the earth's pre-Quaternary period--more than two million years ago--has been studied systematically only since the 1960's, when geologists started to take seriously the concept that the continents have changed position on the earth's surface. In the decades since, the study of pre-Quaternary paleoclimatology has expanded greatly. A wide variety of methods have been developed to study pre-Quaternary...