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The Phanerozoic and the history of Complex Life

Phanerozoic diversity
Fauna and flora from each of the twelve periods of the Phanerozoic. From top left: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene, and Quaternary species. - Wikipedia, art by Gerhard Boeggemann, Mauricio Antón, Mark Witton, Dmitry Bogdanov, Charles R. Knight, Fritz Geller-Grimm, and ABelov2014. - original page


The Phanerozoic is a geologic time period that spans the past 541 million years and is characterized by the evolution and diversification of life on Earth. During this time, the Earth has undergone numerous changes, including periods of mass extinctions, continental drift, and climate change.

Almost the entire Phanerozoic or eon of complex life can fit in the approximate 500 million year interval - evolution from trilobites to dinosaurs to the modern world. Complex animal life appeared slightly earlier, during the Ediacaran period, which was actually the very latest subdivision of the Precambrian, although it was only during the following, Cambrian period that it became diverse.

This time period includes the formation and breakup of the supercontinent Pangea, leading ultimately to the current continents.

For the equivalent time span projected into the future, see the near term very far distant future. Without megascale engineering by a very technologically advanced civilisation, this would mark the absolute limit of life on Earth, due to the sun heating as it grows older.

A short history of the Phanerozoic

The geological time scale provides a framework for understanding the evolution of life and the history of the Earth. This constitutes a time span of about 541 million years and represent a rich history of life on Earth.

Cambrian period: The Cambrian period, which began about 541 million years ago, saw a major evolutionary explosion of life known as the “Cambrian explosion”. A variety of complex organisms emerged during this time, including the first animals with hard skeletons, such as trilobites and brachiopods.

Ordovician period: The Ordovician period, which lasted from about 485 to 443 million years ago, was marked by a continuation of a further diversification of life, including many new invertebrate types such as molluscs and articulate brachiopods. The end of the Ordovician featured an ice age and a mass extinction event.

Silurian period: The Silurian period, which lasted from about 443 to 419 million years ago, saw the emergence of the first land-dwelling animals, including arthropods, the development of the coral reefs, and the colonization of the land by plants. The period is also notable for the evolution radiation of fish, which were mostly armoured, jawless forms.

Devonian period: The Devonian period, which lasted from about 419 to 358 million years ago, is often referred to as the “Age of Fishes” due to the abundance of fish species that evolved during this time. The period also saw the emergence of the first tetrapods, the evolution of forests and the first land-dwelling insects.

Carboniferous period: The Carboniferous period, which lasted from about 358 to 298 million years ago, saw the evolution of the first reptiles and the development of coal-forming swamp forests. Sharks, echinoderms, and amphibians flourished, and terrestrial arthropods grew to large size.

Permian period: The Permian period, which lasted from about 298 to 252 million years ago, was marked by several evolutionary radiations of mammal-like reptiles; synapsids, represented by the pelycosaurs such as the sailback Dimetrodon (early Permian), dinocephalians (middle) and advanced therapsids (late Permian). It ended with the largest mass extinction event in the history of life on Earth.

Triassic period: The Triassic period, which lasted from about 252 to 201 million years ago, was characterised by a diverse assemblage of archosaurs, which replaced the Perian synapsids, as well as many types of marine reptiles. It also saw the evolution of the first mammals and the development of the first dinosaurs and flying reptiles

Jurassic period: The Jurassic period, which lasted from about 201 to 145 million years ago, was characterized by new types of marine reptiles, ammonites, the evolution of giant dinosaurs (the long-necked sauropods), the first birds, and the development of teleost fish.

Cretaceous period: The Cretaceous period, which lasted from about 145 to 65 million years ago, was marked by the evolution of flowering plants and the development of the first modern birds. It included several dynasties of dinosaurs, including, at the very end Cretaceous, the iconic Tyrannosaurus and Triceratops. The period is also notable for the extinction of the dinosaurs, which was likely caused by an asteroid impact.

During the Paleogene Period, which lasted from 66 to 23 million years ago, is divided into the Paleocene, Eocene, and Oligocene, the mammals continued to diversify and evolve into a wide range of forms, including early primates and ungulates. The evolution of mammals was accompanied by major changes in the Earth's climate and geography, including the Paleocene thermal maximum, and later transition from the tropic Paleocene and Eocene to the cooler and drier Oligocene.

This period saw the evolution of modern birds, the formation of the Rocky Mountains, and the first stages of the development of the Gulf Stream, which had a significant impact on global climate.

The Neogene Period from 23 to 2.58 million years ago, saw the rise of primates, including the evolution of early human ancestors such as Australopithecus. During this time, the Earth's climate became more seasonal and the planet saw the formation of the large ice sheets that covered much of the northern hemisphere. The Neogene also saw the evolution of modern species of mammals, including elephants, horses, and whales.

The Quaternary period, which began 2.58 million years ago to present day, and is the shortest geological period in the Phanerozoic Eon. It is known for its Pleistocene megafauna (mammoths, cave lions, woolly rhinos, reindeer, horses, ground sloths, diprotodons) alongside modern animals, the evolution of various hominin (human and human-related) species, and dramatic changes in the climate. It is divided into two epochs: the Pleistocene and the Holocene.

Each of these geological periods represents a unique and important chapter in the history of life on Earth, and collectively they provide us with a comprehensive understanding of the evolution of life and the history of our planet.


This timeline of the last 535 million years is mostly from Wikipedia. Hopefully, these pages will be upgraded at some time. For an earlier and much more complete coverage, see Palaeos

Paleozoic era

Mesozoic era

Bergamodactylus wildi Kellner, 2015; (Pterosauria: Campylognathoididae), from the Late Triassic (Middle Norian - about 215 Mya) of European Pangea. With a wingspan of only 50 cm, this was one of the smaller, as well as one of the earliest, of the Pterosaurs. It would have filled an ecological niche similar to that of modern insectivorous birds. Artwork copyright Nobu Tamura, 2020. Creative Commons Attribution, ShareAlike (CC BY-SA)
Cenozoic Era begins

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