A Brief Overview of the Phanerozoic Eon for Middle School Science Classes

Dec 5, 2024

4 min read

Earth history is a fascinating topic! It is also a massive topic! The reading passage below will teach you all about the Phanerozoic eon. If you want to learn more (and why wouldn't you?!), you can check out my Earth History page. I also have all of my passages available at Teachers Pay Teachers. They come with so many extras to get your students thinking about the content! I also recommend scrolling to the bottom of the page to check out my digital picture book on the Phanerozoic eon!

The Phanerozoic eon is the shortest eon in Earth’s history. It is also the most recent. We are currently living in the Phanerozoic eon.

In Greek, phanerozoic means “visible life.” The eon got its name because scientists thought the first multicellular life evolved during the Phanerozoic eon. Now, we know that multicellular life existed during Proterozoic eon, but the name has stayed the same.

The Phanerozoic eon began with the Cambrian explosion. This was the sudden appearance of a variety of animals at the beginning of the Cambrian period. Every animal phyla except Bryozoa evolved during the Cambrian explosion. These early animals were very different from the animals on Earth today.

The Phanerozoic eon is divided into three eras. The earliest era, the Paleozoic era is the “age of ancient life” because multicellular life developed during the era. The first animals with backbones and nervous systems evolved during the Paleozoic era.

The next era, the Mesozoic era, is known as the “age of middle life” because life continued to evolve during it. It is also known as the “age of dinosaurs” because dinosaurs dominated the Earth’s habitats during the Mesozoic era. We are living in the most recent era of the Phanerozoic eon, the Cenozoic era. This is the “age of recent life” because modern animals evolved during the era. It is also called the “age of mammals” because mammals have dominated Earth during this era.

Throughout the Phanerozoic eon, seafloor spreading has caused the continents to move. A supercontinent from the Proterozoic eon was just breaking up as the Phanerozoic eon began. The continents slowly moved apart and then came together again to form the supercontinent Pangaea. Pangaea started breaking up during the Jurassic period of the Mesozoic era. Over time, the continents took their current forms.

The climate has also changed throughout the Phanerozoic eon. The climate gradually warmed

during the Paleozoic era. The climate of the Mesozoic era was much warmer than it is today.

Most places on Earth were hot and humid. The breakup of Pangaea had a direct effect on Earth’s climate. The Earth cooled throughout the Cenozoic era. The Pleistocene epoch experienced several ice ages where ice sheets extended from the poles to northern Europe and North America.

The animals on Earth continued to evolve in response to the changing climate. The animals best suited to the environment survived, while animals unsuited to the environment went extinct. For example, dinosaurs went extinct at the end of the Cretaceous period because they couldn’t survive in the colder environment. Their huge bodies needed more food than the environment could provide. Mammals survived the extinction because they were small and they would eat anything. They were able to find enough food to survive in the colder environment.

The animals on Earth continued to evolve in response to the changing climate. The animals best suited to the environment survived, while animals unsuited to the environment wentextinct. For example, dinosaurs went extinct at the end of the Cretaceous period because they couldn’t survive in the colder environment. Their huge bodies needed more food than the environment could provide. Mammals survived the extinction because they were small and they would eat anything. They were able to find enough food to survive in the colder environment.

Humans are having an unprecedented effect on the Earth. Deforestation is destroying animals’ habitats, and burning fossil fuels is adding carbon dioxide to the atmosphere. Some scientists believe we are in the middle of a Holocene extinction event. They estimate that nearly thirty percent of plant and animal species will be extinct within the next hundred years. Luckily, humans are also able to help the environment. Reducing fossil fuel consumption is one way we can protect our environment. We can also design ways to protect animal habitats. For the first time in Earth’s history, a mass extinction could be prevented.

Phanerozoic Eon Picture Book

Looking for another way to learn about the Phanerozoic Eon? Check out this picture book version. The pages are a part of my Earth History bundle on Teachers Pay Teachers.