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Phanerozoic Eon

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Last updated date: 17th Jul 2024
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What is Phanerozoic Eon?

Phanerozoic eon means the eon comprising the Paleozoic, Mesozoic, and Cenozoic eras. The phanerozoic eon is the present geological eon in the geological time scale and the era during which abundant plant and animal life have existed. The phanerozoic period covered 541 million years to the present. 

The phanerozoic era begins with the Cambrian period when animals initially developed hard shells preserved in the fossil record.  The time before the phanerozoic era is known as the Precambrian and is divided into Haiden, Arches, and Proterozoic eras.

The period of the phanerozoic eon starts with the instant appearance of the fossilized evidence of several animals phyla, the evolution of those phyla into different forms, the development and emergence of complex plants, the evolution of fish, insects, and tetrapods, and also the development of modern fauna. The plant life on land appeared early in the phanerozoic era. During the phanerozoic eon, the tectonic force which moved into the continent had collected them into a single landmass known as the Pangea (the most latest continent) which then further divided into current continental landmasses. 

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Phanerozoic Meaning 

The term phanerozoic is derived from the Ancient word φανερός (phanerós) meaning visible and ζωή (zōḗ) meaning life, as it was once believed that the life began in Cambrian, the first period of the phanerozoic eon. The term “ phanerozoic” was first introduced by the American geologist George Halcott Chadwick (1876–1953).

The Phanerozoic eon era includes the instant evolution of several animal phyla, the evolution of terrestrial plants, complex plants, fish, and terrestrial animals, and the development of modern faunas and human beings.

Phanerozoic Eon Definition

The phanerozoic eon definition states that it is the interval of geologic time spanning from the appearance of abundant, macroscopic, hard-shelled fossils, approximately 542 million years ago (mya) to the present time.

The phanerozoic timeline given below shows some of the life forms that developed during the phanerozoic era. Life steadily became more diversified and new species developed.  Most of the new-age organisms that emerged from species are now extinct.

Phanerozoic Timeline


Millions of Years Ago

Major Life Forms


0.2( 200,000 years ago)

First humans 


First grasses, grasses started dominating the land



First plant with flowers


First bird on Earth


First mammals on Earth


Age of dinosaur begins



First Reptiles on Earth


First amphibians on Earth 


First insect on Earth


First plant and fungi begin growing on land 


First fish on Earth

Phanerozoic Eon Era

The phanerozoic eon is divided into three eras namely the Paleozoic, the Mesozoic, and the Cenozoic. This phanerozoic eon era is further subdivided into 12 periods. The Paleozoic era experienced the evolution of amphibians, reptiles and fish. The Mesozoic era experienced the evolution of snakes, lizards, crocodiles, mammals, and dinosaurs (including birds).  The Cenozoic era begins with the extinction of non-avian dinosaurs and also undergoes the evolution of great diversity in birds and mammals. Human beings evolved at the end of the Cenozoic era.

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Biodiversity During the Phanerozoic

It has been observed that changes in biodiversity during the Phanerozoic is much better correlated with the hyperbolic model (immensely used in demography and macro sociology) than with exponential and logistic models (commonly used in biology and also applied extensively to fossil biodiversity). 

The logistic models imply that changes in diversity are abided by first-order positive feedback (more ancestors, and more descendants) or negative feedback that arises from the limitation of resources, or both. The hyperbolic model means second-order positive feedback. The hyperbolic pattern of the human population growth emerges from quadratic positive feedback, caused by the interaction of the population size and the rate of technological growth. 

The characteristics of the growth of biodiversity during the Phanerozoic Eon can be similarly judged by feedback between the diversity and community structure complexity. It is recommended that the similarity between the biodiversity curves and human population probably comes from the fact that both are derived from the juxtaposition on the hyperbolic trend of cyclical and random dynamics. 

Phanerozoic Eon Era Facts and Information

  • The phanerozoic eon is defined as the current time in geological time scale.

  • It is the era in which abundant life has existed.

  • The phanerozoic era covers 541 million years and goes back to the time when hard-shelled animals first appeared.

  • The time before the phanerozoic era is known as the Precambrian, and is now divided into Hadean, Archean, and proterozoic eon.

FAQs on Phanerozoic Eon

1. Define Paleozoic Era.

Ans. The paleozoic era is the period in the Earth's history when the complex life evolved, took their initial breath of oxygen on dry land, and all the forerunners of multicellular organisms on Earth began to live. The six periods in the paleozoic era are Cambrian, Ordovician, Silirurian, Devonian, Carboniferous, and Permian.

2. How Was Earth's Climate During the Phanerozoic Eon?

Ans. The phanerozoic eon was divided into three eras namely the Paleozoic, the Mesozoic, and the Cenozoic. The climate of the Earth changed multiple times during the Phanerozoic Eon. At the end of the Precambrian period, much of the planets were covered with glaciers. At the beginning of the Phanerozoic Eon, the climate was warm and humid. Since then Earth's climate has gone through four cycles of frigid areas and warm tropical seas. Some of the organisms survived in the changing climate. Others go extinct when the climate changes too much.

3. How Were the Three Eras of Phanerozoic Eon Named?

Ans. The phanerozoic eon was divided into three eras namely the Paleozoic, the Mesozoic, and the Cenozoic. The eras were named for the kind of fossils that were present. The youngest era is the Cenozoic era meaning new life. This is because fossils are similar to plants and animals that are common today. The paleozoic era is the earliest era which means ancient life. Fossil from the Paleozoic era includes plants and animals that are completely extinct. The Mesozoic era means middle life. The fossils in this era are a mixture of extinct groups and modern groups of plants and animals.