Question

What are the three eras in the phanerozoic eon?

Answer 1

Hint: The geologic time scale (GTS) is a chronological dating methodology used to classify geological layers (stratigraphy) in time. Geologists, palaeontologists, and other Earth scientists use it to define the timing and linkages of geologic events. The time scale was created by studying and observing the strata of rock and their relationships.

Complete answer:
The Phanerozoic Eon is the current geologic aeon in the geologic time scale, and it was characterised by profuse animal and plant life. It spans $541$ million years, beginning with the Cambrian Period when animals first created hard shells that were preserved in the fossil record. The Precambrian period, which preceded the Phanerozoic, is today separated into the Hadean, Archaean, and Proterozoic aeons.

The Phanerozoic is divided into three eras: Paleozoic, Mesozoic, and Cenozoic, each of which is further broken into $12$ periods. Fish, amphibians, and reptiles evolved throughout the Paleozoic period. Lizards, crocodiles, snakes, turtles, mammals, and dinosaurs evolved during the Mesozoic period (including birds). The Cenozoic epoch begins with the demise of non-avian dinosaurs and is characterised by the evolution of tremendous diversity in birds and mammals. Humans appeared at the conclusion of the Cenozoic epoch.

Paleozoic Era –
The Paleozoic Era is a period in Earth's history when complex life forms emerged, took their first breath of oxygen on dry ground, and the forefathers of all multicellular life on Earth began to diversify. The Paleozoic era is divided into six periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.

Mesozoic Era –
The Mesozoic period lasted from $252$ million to $66$ million years. The Mesozoic, colloquially known as "the age of the dinosaurs," saw the birth of many contemporary tetrapods when reptiles ascended to ecological dominance over synapsids. The Mesozoic is divided into three periods: Triassic, Jurassic, and Cretaceous.

Cenozoic Era –
The Cenozoic epoch saw the development of mammals as the dominating animal group, as the dinosaur extinction created substantial available niches. The Cenozoic is divided into three periods: Paleogene, Neogene, and Quaternary.

Note: The Proterozoic-Phanerozoic divide was established $541$ million years ago. The border was established in the nineteenth century with the appearance of the first numerous animal (metazoan) fossils, although several hundred groups (taxa) of metazoa from the older Proterozoic aeon have been identified.