Phanerozoic

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Phanerozoic

The Phanerozoic (Brit. Phanærozoic) 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 animals first appeared. Its name derives from the Greek meaning visible life, referring to the large size of organisms since the Cambrian explosion

Cambrian explosion

The Cambrian explosion or Cambrian radiation was the seemingly rapid appearance of most major groups of complex animals around , as evidenced by the fossil record....
. The time previous to the start of the Phanerozoic was formerly called the Precambrian
Precambrian

The Precambrian is an informal name for the supereon comprising the eon of the geologic timescale that came before the current Phanerozoic eon....
(now divided into the Hadean

Hadean

The Hadean is the Eon before the Archean. It started at Earth formation about 4.6 billion years ago , and ended roughly 3.8 billion years ago, though the latter date varies according to different sources....
, Archaean and Proterozoic

Proterozoic

The Proterozoic is a eon representing a period before the first abundant complex life on Earth. The Proterozoic Eon extended from 2500 annum to 542.0 ? 1.0 Ma , and is the most recent part of the old, informally named ?Precambrian? time....
eons).

The exact time of the boundary between the Phanerozoic and the Proterozoic

Proterozoic

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Cambrian explosion

Hadean

Proterozoic

The Proterozoic is a eon representing a period before the first abundant complex life on Earth. The Proterozoic Eon extended from 2500 annum to 542.0 ? 1.0 Ma , and is the most recent part of the old, informally named ?Precambrian? time....
is slightly uncertain. In the 19th Century, the boundary was set at the first abundant metazoan fossil

Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
s. But several hundred taxa

Taxon

A taxon or taxonomic unit is a name designating an organism or a group of organisms. In biological nomenclature according to Carl Linnaeus, a taxon is assigned a taxonomic rank and can be placed at a particular level in a systematic hierarchy reflecting evolutionary relationships....
of Proterozoic

Proterozoic

The Proterozoic is a eon representing a period before the first abundant complex life on Earth. The Proterozoic Eon extended from 2500 annum to 542.0 ? 1.0 Ma , and is the most recent part of the old, informally named ?Precambrian? time....
metazoa have been identified since systematic study of those forms started in the 1950s. Most geologist

Geologist

For other uses, see Geologist .A geologist is a contributor to the science of geology, studying the physical structure and processes of the Earth and planets of the solar system ....
s and paleontologists would probably set the Proterozoic-Phanerozoic boundary either at the classic point where the first trilobite

Trilobite

Trilobites are extinction marine arthropods that form the class Trilobita. They appeared in the Early Cambrian period and flourished throughout the lower Paleozoic era before beginning a drawn-out decline to extinction when, during the Late Devonian extinction, all trilobite orders, with the sole exception of Proetida, died out....
s and archaeocyatha

Archaeocyatha

The Archaeocyatha or archaeocyathids were Sessility , reef-building Marine organisms of warm tropical and subtropical waters that lived during the early Cambrian period....
appear; at the first appearance of a complex feeding burrow called Trichophycus pedum
Trichophycus pedum

Trichophycus pedum is regarded as the earliest widespread complex trace fossil. Its earliest appearance, which was contemporaneous with the last of the Ediacaran biota, is used to define the dividing line between the Ediacaran and Cambrian Period ....
; or at the first appearance of a group of small, generally disarticulated, armored forms termed 'the small shelly fauna

Small shelly fauna

The small shelly fauna or small shelly fossils, abbreviated to SSF, are biomineralization fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian period ....
'. The three different dividing points are within a few million years of each other.

The Phanerozoic is divided into three eras: the Paleozoic

Paleozoic

The Paleozoic or Palaeozoic Era is the earliest of three geology Era of the Phanerozoic Eon . The Paleozoic spanned from roughly , and is subdivided into six period ; from oldest to youngest they are: the Cambrian, Ordovician, Silurian, Devonian period, Carboniferous, and Permian...
, Mesozoic

Mesozoic

The Mesozoic Era is one of three Geologic time scale of the Phanerozoic eon . The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the 'Mesozoic' was 'Secondary' ....
, and Cenozoic

Cenozoic

The Cenozoic Era...
. In the older literature, the term Phanerozoic is generally used as a label for the time period of interest to paleontologists, but that use of the term seems to be falling into disuse in more modern literature.

The time span of the Phanerozoic includes the rapid emergence of a number of animal phyla; the evolution

Evolution

In biology, evolution is change in the heritability trait of a population of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and selection....
of these phyla into diverse forms; the emergence of terrestrial plant

Plant

Plants are Life organisms belonging to the Kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae....
s; the development of complex plants; the evolution of fish

Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
; the emergence of terrestrial animals; and the development of modern faunas. During the period covered, continent

Continent

A continent is one of several large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents ? they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia ....
s drifted about, eventually collecting into a single landmass known as Pangea and then splitting up into the current continental landmasses.

Phanerozoic

See also