scientific study of the climatic conditions of past geologic ages. Paleoclimatologists seek to explain climate variations for all parts of the Earth during any given geologic period, beginning with the time of the Earth's formation. Many related fields contribute to the field of paleoclimatology, but the basic research data are drawn mainly from geology and paleobotany; speculative attempts at explanation have come largely from astronomy, atmospheric physics, meteorology, and geophysics.

Two major factors in the study of both ancient and present-day climatic conditions of the Earth are the changes in the relationship between the Earth and the Sun (e.g., the slight alteration in the configuration of the Earth's orbit) and the changes in the surface of the planet itself (such phenomena as volcanic eruptions, mountain-building events, the transformations of plant communities, and the dispersal of the continents after the breakup of the supercontinent Pangea). Some of the questions that were studied in the past have been largely explained. Paleoclimatologists found, for example, that the warmth of the northern hemispheric landmasses during at least 90 percent of the last 570 million years is mainly due to the drift of the continents across the latitudes; until about 150 million years ago, both North America and Europe were much closer to the Equator than they are today. Other questions, such as the reasons behind the irregular advances and retreats of the ice sheets (i.e., glacial and interglacial episodes), are much more difficult to explain, and no completely satisfactory theory has been presented.