Phanerozoic Eon


Phanerozoic Eon
Span of geologic time from с 543 million years ago, the end of the Proterozoic Eon, to the present.

The Phanerozoic, the eon of visible life, is divided into three major eras: the Paleozoic, Mesozoic, and Cenozoic. Although life originated in Precambrian time, it was in the Phanerozoic that many forms arose and evolved. The Earth gradually assumed its present configuration and physical features through such processes as plate tectonics, mountain building, and glaciation.

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      the span of geologic time extending about 542 million years from the end of the Proterozoic Eon to the present. The Phanerozoic, the eon of visible life, is divided into three major spans of time largely on the basis of characteristic assemblages of life-forms: the Paleozoic, Mesozoic, and Cenozoic eras. Although life clearly originated at some time, probably quite early, in the Proterozoic Eon, not until the Phanerozoic did a rapid expansion and evolution of forms occur and fill the various ecological niches available. The key to this great Phanerozoic expansion appears to lie in the development of plants able to carry out the photosynthetic process and thus release free oxygen into the atmosphere. Before this time, the Earth's atmosphere contained negligible amounts of free oxygen, and animals, in which energy transfers involving the process of respiration are critical, were unable to develop. During the Phanerozoic, the Earth gradually assumed its present configuration and physical features through such processes as continental drift, mountain building, and continental glaciation. Thus, although the Phanerozoic Eon represents only about the last one-eighth of time since the Earth's crust formed, its importance far exceeds its relatively short duration.

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Universalium. 2010.

Look at other dictionaries:

  • Phanerozoic eon — noun the period from about 5,400 million years ago until the present • Syn: ↑Phanerozoic, ↑Phanerozoic aeon • Instance Hypernyms: ↑eon, ↑aeon • Part Meronyms: ↑Cenozoic, ↑Cenozoic era, ↑ …   Useful english dictionary

  • Phanerozoic — [fan΄ər ə zō′ik] adj. [< Gr phaneros (see PHANEROGAM) + ZOIC] [sometimes p ] designating or of the geologic eon usually subdivided into the Paleozoic, Mesozoic, and Cenozoic eras designating or of the geologic eon usually subdivided into the… …   English World dictionary

  • eon — /ee euhn, ee on/, n. 1. an indefinitely long period of time; age. 2. the largest division of geologic time, comprising two or more eras. 3. Astron. one billion years. Also, aeon. [see AEON] * * * I Long span of geologic time. In formal usage,… …   Universalium

  • Phanerozoic — noun the period from about 5,400 million years ago until the present • Syn: ↑Phanerozoic eon, ↑Phanerozoic aeon • Instance Hypernyms: ↑eon, ↑aeon • Part Meronyms: ↑Cenozoic, ↑Cenozoic era …   Useful english dictionary

  • Phanerozoic aeon — noun the period from about 5,400 million years ago until the present • Syn: ↑Phanerozoic, ↑Phanerozoic eon • Instance Hypernyms: ↑eon, ↑aeon • Part Meronyms: ↑Cenozoic, ↑Cenozoic era, ↑ …   Useful english dictionary

  • Phanerozoic — 1. adjective Of, or relating to the geologic eon from about 570 million years ago to the present; comprises the Paleozoic, Mesozoic and Cenozoic eras. 2. noun The Phanerozoic eon …   Wiktionary

  • Eón Fanerozoico — Saltar a navegación, búsqueda Supereón Eón M. años   Fanerozoico 542,0 ±1,0 Precámbrico Proterozoico 2.500 Arcaico 3.800 …   Wikipedia Español

  • Phanerozoic — The Phanerozoic (occasionally Phanaerozoic) Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 545 million years and goes back to the time when diverse hard shelled… …   Wikipedia

  • Phanerozoic — adjective Etymology: Greek phaneros + English 2 zoic Date: 1930 of, relating to, or being an eon of geologic history that comprises the Paleozoic, Mesozoic, and Cenozoic or the corresponding systems of rocks see geologic time table • Phanerozoic… …   New Collegiate Dictionary

  • Phanerozoic — /fan euhr euh zoh ik/, Geol. n. 1. the eon comprising the Paleozoic, Mesozoic, and Cenozoic eras. adj. 2. of or pertaining to this eon. [1925 30; < Gk phaneró(s) manifest, visible + ZO + IC] * * * …   Universalium


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