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Paleontology is the study of ancient life-forms of past geologic periods. Paleontologists learn about ancient animals and plants mainly through the study of fossils. These may be the actual remains of the animal or plant or simply traces the organism left behind (tracks, burrows, or imprints left in fine sediments).

Paleozoology is the subdiscipline of paleontology that focuses on the study of ancient animal life. Paleobotany is the subdiscipline that focuses on the study of the plant life of the geologic past.

Geologic time is a scale geologists have devised to divide Earth's 4.5-billion-year history into units of time. A unit is defined by the fossils or...