Compare and contrast relative and radiometric dating

The tables of geologic time spans, presented here, agree with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS).The primary defined divisions of time are eons, in sequence the Hadean, the Archean, the Proterozoic and the Phanerozoic.The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time.It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history.This clock representation shows some of the major units of geological time and definitive events of Earth history.The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now regarded as 4.0 Ga (billion years ago).The first three of these can be referred to collectively as the Precambrian supereon.

The adjectives are capitalized when the subdivision is formally recognized, and lower case when not; thus "early Miocene" but "Early Jurassic." Evidence from radiometric dating indicates that Earth is about 4.54 billion years old.Leonardo da Vinci (1452–1519) concurred with Aristotle's interpretation that fossils represented the remains of ancient life.The 11th-century Persian geologist Avicenna (Ibn Sina, died 1037) and the 13th-century Dominican bishop Albertus Magnus (died 1280) extended Aristotle's explanation into a theory of a petrifying fluid.For example, the boundary between the Cretaceous period and the Paleogene period is defined by the Cretaceous–Paleogene extinction event, which marked the demise of the non-avian dinosaurs and many other groups of life.

Older time spans, which predate the reliable fossil record (before the Proterozoic eon), are defined by their absolute age.He also formulated the law of superposition, which states that any given stratum is probably older than those above it and younger than those below it.

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