Major Geologic Eras in the Phanerozoic Eon

A general description of the three geologic eras: Paleozoic, Mesozoic and Cenozoic; during the Phanerozoic Eon.

Paleozoic Era

The Paleozoic Era is the earliest of the three geologic eras. It ranged from 542 – 251 million years ago. The Paleozoic Era consisted of six geologic periods, which were (from oldest to youngest): Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. The Paleozoic Era took up more than half of the Phanerozoic Eon, which was around 300 million years. The Paleozoic Era also includes the appearances of hard-shelled animals to all kinds of new plants.

Mesozoic Era

The Mesozoic Era is the middle era of the three geologic eras. It lasted for 180 million years. The Paleozoic Era consisted of three geologic periods, which were (from oldest to youngest): Triassic, Jurassic and Cretacious. The Paleozoic Era also includes the appearances of hard-shelled animals to all kinds of new plants. After the great Permian extinction, many ecological niches were empty, which were filled by organisms later. A few million years after the Permian extinction, dinosaurs, large reptiles, avian (flying) creatures and marine creatures stared to show up during the Triassic Period. As the Jurassic and Cretacious Period cam along, the climate of the earth changed, for the better of the organisms. The first birds and placental mammals started showing up during these periods. But, as the temperature continued to increase, the large reptiles and all dinosaurs slowly started to disappear, while the birds and mammals thrived in population and continued living. Lots of small reptiles like snakes also continued to live.

Cenozoic Era

The Cenozoic Era is the earliest era of the three geologic eras, which still continues today. It has had a current duration of 65.5 million years so far. The Cenozoic Era consists of two periods, Tertiary and Quaternary, which were also divided into smaller sub divisions. The Tertiary Period was divided into two subdivisions (oldest to youngest), Paleogene, and Neogene. These two subdivisions were also divided into smaller groups called epochs. The Paleogene division consisted of three epochs, which were (from oldest to youngest) Paleocene, Eocene and Oilgocene. The Neogene division consisted of two epochs, which were (from oldest to youngest) Miocene and Pliocene. The Quaternary period only consist of one epoch, and that is the Pleistocene, the epoch in which we live in. The Cenozoic era began at the end of the Mesozoic Era’s Cretaceous Period, with the extinction of all the non-avian (land) dinosaurs. During this Era, mammals were and still are the largest animals on the land. Evolution was something that occurred as well, many plants and animals evolved during this era as well. Something else that changed was the geography of the earth. Since Pangea had split apart, continental drift caused the tectonic plates of the earth to slowly move apart, and within the time span of millions of years, the continental plates moved into the spots as we see them now on our world maps.

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