Phanerozoic Eon: Facts & Timeline

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  • 0:01 Phanerozoic Eon
  • 0:25 Paleozoic Era
  • 1:13 Mesozoic Era
  • 1:59 Cenozoic Era
  • 2:39 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 Phanerozoic Eon is the current eon in Earth's history. The Phanerozoic began 542 million years ago with the Cambrian explosion and continues to the present. This lesson covers the events that have occurred during this time span.

The Phanerozoic Eon

The Phanerozoic Eon is a period of geological history that spans 542 million years and is typically subdivided into three eras. These eras are:

  • Paleozoic Era: 542 to 251 million years ago
  • Mesozoic Era: 251 to 65 million years ago
  • Cenozoic Era: 65 million years ago to present

Paleozoic Era

The Paleozoic Era began with a metaphorical explosion of life. The Cambrian explosion, as it was called, occurred 542 million years ago saw single-celled bacteria evolve into an abundance of diverse organisms. The emergence of all the animal phyla that exist today can trace their origins back to the 40 million-year span that was the Cambrian explosion.

While the beginning of the Paleozoic is often described as an 'explosion of life,' the end of the period 251 million years ago was more like an 'implosion of life.' As much as 96% of all life on Earth went extinct during the event known as the P-T extinction. Although the cause is not entirely understood, the P-T extinction almost turned Earth into a lifeless planet.

Mesozoic Era

What little life that was left on Earth after the Paleozoic repopulated on a grand scale. The Mesozoic Era saw the rise of the dinosaurs. The continents as we know them today have undergone some major changes over the years. During the Mesozoic Era, the continents were combined into a supercontinent known as Pangaea. During the Jurassic period, dinosaurs had become the largest and most dominant form of life on Earth.

The dinosaurs reigned on Earth for almost 200 million years, before devastation struck again—this time in the form of an asteroid impact. Off the coast of Mexico 65 million years ago, an asteroid slammed into the ocean causing the extinction of 75% of all life on Earth, most notably the non-avian dinosaurs.

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