The Ordovician period is a part of the Paleozoic era. It occurred between the Cambrian and Silurian Eras millions of years ago. The Ordovician was at first thought to be part of the previous periods, but in 1879, Sir Charles Lapworth pointed out the differences that distinguished it as a separate geological period. He named the period Ordovician for an ancient Celtic tribe that once inhabited the United Kingdom, the Ordoves. The Ordovician period lasted from 488 million years ago to 444 million years ago.
The continents that drifted across the planet’s oceans came together during the Ordovician period. Africa, Australia, South America, Antarctica formed a great land mass called Gondwana. Gondwana moved southward, finally settling at the South Pole. North America, which was largely underwater, Europe and the tropics combined into a super-continent called Laurentia that straddled the equator.
The changing continents reflected the many tectonic shifts that occurred below the ocean floor during the Ordovician age. Uplifts under the shallow seas and some plates moved northward. Volcanic activity increased during this period and ocean currents changed significantly. Sea levels flooded the land masses and receded a number of times across the globe. When glaciers formed at the end of the era, sea levels dropped severely causing a disruption in environment that affected many life forms.
During the Ordovician age, the climate was warm and wet. Sea levels rose almost 2000 feet above levels found today. After Gondwana moved to the South Pole, glaciers began to form that created a 20-million-year ice age that caused the seas that teamed with life to shrink away.
The Life Forms
After the Cambrian extinction, oxygen levels began to rise and seas receded. The first plants developed on land. The oceans teemed with new life, including corals, starfish, brachiopods and eel-like creatures. Snails, clams, and cephalopods appeared for the first time. Variations within family groups of animals widened greatly. Animals called conodonts began to develop calcareous skeletons.
The Ordovician era both began with an extinction of many life forms and ended with an extinction. The Ordovician extinction that occurred at the end of the period came in two waves, probably because of changing sea levels and glacier formation. Scientists believe up to 60 percent of marine invertebrates went extinct.
The Ordovician era both began and ended with extinction events that deciminated many of the life forms that existed. Even so, the Earth’s life forms managed to replenish themselves and adapt to the changed conditions that existed at each point.