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| Paleoanthropology is a multidisciplinary approach to the analysis of primate and human evolution, relying primarily on information from the fossil record (and the archaeological record for human evolution). Dating methods provide the means by which to place fossils and other ancient data in sequence over time. Relative dating methods provide information on which samples are older or younger, but not the exact age. A commonly used relative dating method is stratigraphy, which makes inferences about age from a specimen's position in geologic strata—the deeper the specimen, the older it is. Chronometric dating methods make use of radioactive decay and other physical phenomena to provide an estimate of the actual age of a specimen. Commonly used methods of chronometric dating include carbon-14 dating for relatively "recent" specimens (less than 50,000 years old) and argon dating for very ancient specimens. The fossil record provides a direct view on what our ancestors looked like and how they adapted. Analysis of fossil remains involves considering the relationships of a given specimen to known species in order to classify it into a known species or to designate a new species. Anatomical variation within species, such as due to sex and age, is important in distinguishing between fossil remains. Reconstruction of our ancestor's behavior makes use of information we can obtain from ancient environments including diet. Analysis of the archaeological record helps us understand human evolution over the past 2.5 million years, following the origin of stone tool technology. Our understanding of the creation and function of stone tools is enhanced through experimental archaeology. Attempts to reconstruct behavior can also benefit by inferences made from the behavior of living primates, particularly our closest living relatives, the African apes. The earth is 4.6 billion years old. Roughly half a billion years ago, the first vertebrates appeared, followed by the first amphibians, and then the first reptiles. The therapsids, or mammal-like reptiles, were one of the first groups of reptiles. The therapsids eventually died out under competition from the dinosaurs, but some evolved into primitive mammals. When the dinosaurs and other organisms died in a mass extinction over 65 million years ago, the mammals had the opportunity to expand, and they underwent a series of adaptive radiations. One group of mammals, the primates, appeared about 50 million years ago. |