A Brief Overview of the Ordovician Period for Middle School Science Classes

Dec 14, 2024

3 min read

Earth history is a fascinating topic! It is also a massive topic! The reading passage below will teach you all about the Ordovician Period. 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 Ordovician Period!

Ordovician Period Reading Passage for Middle School Science

Naming the Ordovician Period

In the 1830s, Adam Sedgwick and Robert Murchison named the Cambrian and Silurian periods. However, they couldn't agree on when the Cambrian period ended and the Silurian period began. In 1873, geologist Charles Lapworth suggested a new period between the Cambrian and Silurian periods. He called it the Ordovician period after the Ordovices, an ancient tribe from North Wales.

Lapworth based his new period on graptolite fossils found in the fossil record between 488 and 443 million years ago. These tiny sea creatures existed during the Cambrian period, but they were more common during the Ordovician period.

Climate

The climate of the Earth was warm during the Ordovician period because of carbon dioxide in the atmosphere. Scientists believe there was fourteen to sixteen times more carbon dioxide in the atmosphere during the Ordovician period than today. The carbon dioxide came from the many volcanic eruptions during the period. A warmer temperature meant high sea levels. Sea levels were almost two thousand feet higher during the Ordovician period than they are today.

Life

During the Ordovician period, life was mostly in the water. New species replaced the creatures that had died during the mass extinction that ended the Cambrian period. The increase in life during this period is called the Ordovician radiation. Fish first appeared during the Ordovician period. They didn’t have jaws, fins, or brains, but they did have a notochord. A notochord is an early spinal cord. At the bottom of the sea, the first creatures with primitive backbones appeared.

The Ordovician period had three times as many species as the Cambrian period. Corals, bryozoans, brachiopods, mollusks, echinoderms, sea urchins, starfish, sea lilies, sea snails, and sea cucumbers all lived in the oceans. The main predators of the Ordovician seas were cephalopods. They were similar to today’s octopi and squid.

Plants

The first primitive plants appeared on land during the Ordovician period. Cryptospores lived in damp habitats across the globe. These were the precursors to nonvascular plants. Moss is an example of a nonvascular plant today.

Trilete spores were the Ordovician period precursors to vascular plants. Vascular plants include flowers, trees, and most other plants. They have systems of xylem and phloem to transport water and nutrients throughout the plant. Both cryptospores and trilete spores evolved from red and green algae.

Animal Habitats

Scientists have found fossilized burrows in mud from the Ordovician period. The burrows most likely came from arthropods. Scientists hypothesized that as sea levels dropped, these animals were stranded on land and survived by digging burrows.

Other new habitats were also created during the Ordovician period. Corals built reefs in the shallow waters around the continents. These reefs provided homes for small sea creatures and became new ecosystems.

Mass Extinction

Like the Cambrian period, the Ordovician period ended with a mass extinction. Over 85% of the Earth’s species went extinct over a period of two million years. It was the second largest extinction in Earth's history.

In the early phase of the extinction, graptolites, brachiopods, and trilobites started dying off, but scientists aren’t sure why. Then, the supercontinent Gondwana settled into position at the South Pole. The freezing temperatures on the continent caused giant glaciers to form. These glaciers trapped seawater, and sea levels dropped.

At the same time, global carbon dioxide levels decreased. Fewer volcanoes were erupting, and more organisms were using carbon dioxide for photosynthesis. Also, the white snow of the glaciers reflected sunlight back into space, so Earth’s temperatures decreased. Lower sea levels and cooler temperatures caused the second phase of the extinction. The Ordovician period ended with extinction, but life continued.

Ordovician Period Picture Book

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