The study of the physical, chemical, and biological processes and products of the earth; simply, the study of the history of the earth and an understanding of the time scale over which man developed. Geology's aims overlap considerably with those of archaeology, particularly in the prehistoric periods. For example, work on the stratigraphy of the Quaternary to provide a geological chronology for the study of the reconstruction of environmental changes throughout the Quaternary forms an essential background to all archaeology. The palaeontology of fossil hominids and the other animals that lived at the same time is another area in which geology and archaeology overlap. The geological methods of dating such as radiocarbon, palaeomagnetism, and potassium-argon form the basis of most prehistoric chronologies. Geophysical techniques are used for the location of sites and petrology traces the origins of stone implements and inclusions in pottery.