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Concept
Phanérozoïque
Résumé
The Phanerozoic is the current and the latest of the four geologic eons in the Earth's geologic time scale, covering the time period from 538.8 million years ago to the present. It is the eon during which abundant animal and plant life has proliferated, diversified and colonized various niches on the Earth's surface, beginning with the Cambrian period when animals first developed hard shells that can be clearly preserved in the fossil record. The time before the Phanerozoic, collectively called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.
The time span of the Phanerozoic starts with the sudden appearance of fossilised evidence of a number of animal phyla; the evolution of those phyla into diverse forms; the evolution of plants; the evolution of fish, arthropods and molluscs; the terrestrial colonization and evolution of insects, chelicerates, myriapods and tetrapods; and the development of modern fauna dominated by vascular plants. During this time span, tectonic forces which move the continents had collected them into a single landmass known as Pangaea (the most recent supercontinent), which then separated into the current continental landmasses.
The term Phanerozoic derives from the Ancient Greek words φανερός (), meaning visible, and ζωή (), meaning life; since it was once believed that life began in the Cambrian, the first period of this eon. The term "Phanerozoic" was coined in 1930 by the American geologist George Halcott Chadwick (1876–1953).
The Proterozoic-Phanerozoic boundary is at 538.8 million years ago. In the 19th century, the boundary was set at time of appearance of the first abundant animal (metazoan) fossils but several hundred groups (taxa) of soft-bodied metazoa of the preceding Proterozoic eon have been identified since the systematic study of those forms started in the 1950s, known as the Avalon Explosion. The transition from the largely sessile Precambrian biota to the active mobile Cambrian biota occurred early in the Phanerozoic.
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