The Cenozoic Era: Definition, Time Period & Facts

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  • 0:00 Cenozoic Era
  • 0:33 KT Extinction
  • 1:04 Age of the Mammals
  • 1:37 Continental…
  • 2:32 Lesson Summary
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Lesson Transcript
Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

The Cenozoic Era spans the previous 65 million years of Earth's history, beginning with the extinction of flightless dinosaurs and continuing up to the present. This lesson covers the events that shaped the Cenozoic Era.

Cenozoic Era

The Cenozoic Era began 65 million years ago with an asteroid impact that killed off a majority of the dinosaurs and ends at the present day. The Cenozoic is commonly divided into three periods:

  • Paleogene (65.5 to 23.03 million years ago)
  • Neogene (23.03 to 2.6 million years ago)
  • Quaternary (2.6 million years ago to present)

KT Extinction

As the dinosaurs roamed the Earth 65 million years ago, an asteroid slammed into the coast of present day Mexico. The impact and its aftermath were strong enough to cause the extinction of the non-avian dinosaurs, such as the brontosaurus. This is commonly referred to as the KT Extinction. The extinction of dinosaurs, the dominant predator on Earth for over 200 million years, would lead to a shake up in the food chain that would allow mammals to increase their dominance.

Age of the Mammals

Small mammals that had commonly been food for the dinosaurs were able to thrive, evolve, and grow. Mammals such as saber tooth tigers and woolly mammoths grew to massive sizes and worked their way to the top of the food chain.

In the jungles of Africa, chimpanzees were able to thrive and evolve as well. Roughly five million years ago, humans genetically diverged away from chimpanzees, eventually evolving into our present form. As humans evolved, we began to migrate and use the surrounding environment to our advantage.

Continental Positioning and Climate

A picture of the Earth at the beginning of the Cenozoic Era would look somewhat similar to a picture of the Earth today. The supercontinent of Pangea that existed during the time of the dinosaurs had split apart by the Cenozoic, and the continents were on their paths to where they are today.

In the Cenozoic Era, the Earth began a long period of cooling, caused in part by the continents shifting into their current positions. As South America separated from Antarctica, a global current of cold water was brought to the surface, cooling the surface temperature of the ocean and the atmosphere.

Another change in ocean currents was caused by the connection of North and South America. The new land mass caused a change in ocean currents and led to the cooling of the Arctic. The Arctic cooling led to glaciers expanding over North America, creating some of the land formations we see today, such as the U-shaped valley of Yosemite.

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