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.
High Carbon Dioxide Levels
There was a lot more carbon dioxide in the air during the Ordovician period. The carbon dioxide came from the many volcanic eruptions during the period. The carbon dioxide made the climate warm. A warmer temperature meant high sea levels. Sea levels were almost two thousand feet higher during the Ordovician period than they are today.
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.
The first primitive plants appeared on land during the Ordovician period. Cryptospores lived in damp habitats across the globe. These were similar to nonvascular plants. Moss is an example of a nonvascular plant today.
Cryptospores and Trilete Spores
Trilete spores were similar 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.
Scientists have found fossilized burrows in mud from the Ordovician period. The burrows most likely came from arthropods like millipedes. Scientists believe 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.
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.
Less Carbon Dioxide
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.
End of the Period
Lower sea levels and cooler temperatures caused the second phase of the extinction. The Ordovician period ended with extinction, but life continued.