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Paleontology is the study of prehistoric life, including organisms' evolution and interactions with each other and their environments. As a "historical science" it tries to explain causes rather than conduct experiments to observe effects. Although 5th century BC and medieval thinkers made what would now be called paleontological observations, the science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. Paleontology lies on the border between biology and geology, and also shares with archeology a border that is difficult to define. It now uses techniques drawn from a wide range of sciences, including biochemistry, mathematics and engineering. Fossils found in China since the 1990s have provided new information about the earliest evolution of animals, early fish, dinosaurs and the evolution of birds and mammals. As knowledge has increased, paleontology has also developed specialised subdivisons, some of which focus on different types of fossil organisms while others focus on ecological and environmental aspects such as ancient climates.

Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating, which provide absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy. Classifying ancient organisms is also difficult, as many do not fit well into the Linnean taxonomy that is commonly used for classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics, which investigates evolutionary "family trees" by applying the analytic techniques of cladistics to aspects of organisms's biochemistry, mainly DNA and RNA. Molecular phylogenetics has also been used to estimate the dates at which branches of "family trees" diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend.

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