Ordovician

The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era, and the second of twelve periods of the Phanerozoic Eon. It lasted for 43.75 million years, from the end of the Cambrian Period 486.85 million years ago to the start of the Silurian Period 443.1 million years ago.

The Ordovician was named after the Welsh tribe of the Ordovices and was defined by Charles Lapworth in 1879. Lapworth introduced this period to settle a disagreement between scientists who were placing the same rock layers in North Wales in either the Cambrian or Silurian systems. He noticed that the fossil fauna in these layers were different, so he created a new system for them. The Ordovician became an official geologic period in 1960, long after Lapworth's death.

Life was very active during the Ordovician. Invertebrates like molluscs and arthropods were common in the oceans, and some arthropods may have begun living on land. The first land plants appeared, and fish, the first true vertebrates, kept evolving. A time known as the Great Ordovician Biodiversification Event saw many new kinds of life. The end of the Ordovician was marked by extinction events that changed life on Earth. During this period, about 100 times more meteorites hit Earth each year than today, in what is called the Ordovician meteor event. Some scientists think this might have been caused by a ring system around our planet at the time.

Subdivisions

In 2008, an international system was created to divide the Ordovician Period into smaller parts. Before this, different areas like Baltoscandic, British, Siberian, North American, Australian, Chinese, Mediterranean, and North-Gondwanan each had their own ways of organizing these time periods, which are still used in some places today.

Paleogeography and tectonics

During the Ordovician, the southern continents came together to form Gondwana, stretching from north of the equator to the South Pole. Large oceans covered much of the world, including the Panthalassic Ocean in the north. Continents such as Laurentia (in modern-day North America), Siberia, and Baltica (northern Europe) were far apart, allowing unique animal communities to develop.

The Ordovician was a time of great tectonic activity, with mountains forming mainly along the edges of continents rather than from collisions between whole continents. Islands and smaller land pieces moved and joined larger continents, changing the world’s landscapes. One notable event was the formation of the Appalachian Mountains when volcanic islands crashed into Laurentia. Despite many changes, life continued to thrive during this exciting period.

Ordovician meteor event

The Ordovician meteor event may have been a time when many meteors fell to Earth about 467.5 million years ago. This happened when a large space rock broke apart, possibly creating a temporary ring of debris around our planet. Scientists have found many craters from this event, but it did not cause any major changes to life on Earth.

Geochemistry

The Ordovician was a time when the oceans had special chemistry that encouraged the formation of a mineral called calcite. This mineral, made from calcium carbonate, was the main material that formed on the ocean floor. Many sea creatures also built their skeletons from this calcite.

During this period, animals and large algae played a big role in creating these calcite deposits, unlike earlier times when tiny organisms were the main source.

Climate and sea level

The early Ordovician had a very hot climate, similar to very warm periods in more recent times, with high levels of carbon dioxide in the air. As the period continued, the Earth cooled, leading to a more temperate climate and eventually an ice age in its later stages.

During the Ordovician, sea levels were higher than at any other time in the Paleozoic Era. The seas rose steadily during the early part of the period and then levelled off. Towards the end of the Ordovician, cooling temperatures caused sea levels to drop for about three million years. There is evidence that glaciers formed on parts of Gondwana, which included areas that are now Africa and South America, as these landmasses were close to the South Pole at the time. These glaciers helped create ice caps and influenced sea levels throughout the period.

Life

The Ordovician period was a time when many types of sea creatures flourished. Near the end of this period, some groups, like certain ancient shellfish called conodonts and tiny floating animals called planktonic graptolites, faced big changes that affected their survival. Some groups of trilobites, which were like odd-looking bugs with hard shells, completely disappeared. Other sea animals, such as brachiopods, bryozoans, and echinoderms, were also strongly impacted.

Life in the Ordovician seas became more complex and diverse than ever before. Many animals developed new ways to protect themselves or find food. For example, some trilobites grew spines or changed shape to avoid being eaten. Brachiopods became very common and lived in many different ocean environments. Corals began forming reefs, and the first known animals with backbones might have appeared during this time. The world’s oceans were full of new and interesting creatures, showing how life was constantly changing and adapting.

End of the period

The Ordovician period ended with a series of extinction events, making it the second largest of the five major extinction events in Earth's history. These events happened about 447–444 million years ago, marking the transition from the Ordovician to the Silurian Period. During this time, about 49% of marine animal families disappeared, including many types of brachiopods, bryozoans, trilobites, conodonts, and graptolites.

Scientists believe these extinctions were caused by a sudden drop in temperature, leading to an ice age. This change may have been triggered by lower carbon dioxide levels in the atmosphere, possibly due to volcanic activity or the growth of plants on land. As glaciers formed, sea levels fell, destroying many habitats and reducing the number of species. Life slowly recovered after the glaciers melted, but many families of organisms took a long time to return.