Ordovician

The Ordovician is a geologic period and system. It is the second of six periods of the Paleozoic Era. It is also the second of twelve periods of the Phanerozoic Eon. It lasted for 43.75 million years. It started after the Cambrian Period 486.85 million years ago. It ended before the Silurian Period 443.1 million years ago.

The Ordovician was named after the Welsh tribe of the Ordovices. A scientist named Charles Lapworth defined it in 1879. Lapworth introduced this period to solve a problem. Scientists could not agree on where to place certain rock layers in North Wales. They were unsure if the layers belonged to the Cambrian or Silurian systems. Lapworth saw 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. This was long after Lapworth's death.

Life was very active during the Ordovician. Invertebrates like molluscs and arthropods lived in the oceans. Some arthropods may have started living on land. The first land plants appeared. Fish, the first true vertebrates, kept evolving. Many new kinds of life appeared during a time called the Great Ordovician Biodiversification Event. The end of the Ordovician had extinction events that changed life on Earth. During this time, many more meteorites hit Earth each year than today. This 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, a new system was made to split the Ordovician Period into smaller parts. Before this, many areas like Baltoscandic, British, Siberian, North American, Australian, Chinese, Mediterranean, and North-Gondwanan each had their own ways of organizing these times. Some places still use their old ways today.

Paleogeography and tectonics

During the Ordovician, the southern continents joined together to form Gondwana. This huge land stretched 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. This allowed many different animal communities to develop.

The Ordovician was a time when the Earth’s surface changed a lot. Mountains formed mainly along the edges of continents, not from big crashes between whole continents. Islands and smaller pieces of land moved and joined larger continents. One big change was the formation of the Appalachian Mountains when volcanic islands crashed into Laurentia. Even with all these changes, life kept growing and thriving.

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. It might have created a temporary ring of debris around our planet. Scientists have found many craters from this event, but it did not change life on Earth in a big way.

Geochemistry

The Ordovician was a time when the oceans had special chemistry that helped make a mineral called calcite. This mineral, made from calcium carbonate, formed on the ocean floor. Many sea creatures also used this calcite to build their skeletons.

During this period, animals and large algae helped create these calcite deposits, which was different from earlier times when tiny organisms were the main source.

Climate and sea level

The early Ordovician had a very hot climate, like very warm times in the past. There was a lot of carbon dioxide in the air. As time went on, the Earth cooled. This led to a milder climate and later, an ice age.

During the Ordovician, sea levels were higher than at any other time in the Paleozoic Era. The seas rose in the early part of the period and then stayed the same. Towards the end, cooling temperatures made sea levels drop for about three million years. Glaciers formed on parts of Gondwana, which included areas that are now Africa and South America. These landmasses were close to the South Pole at the time. The glaciers helped create ice caps and changed sea levels during this period.

Life

The Ordovician period was a time when many sea creatures thrived. Near the end, some groups, like ancient shellfish called conodonts and tiny floating animals called planktonic graptolites, faced big changes that made it hard for them to survive. Some groups of trilobites, which were like odd 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 events that caused many kinds of sea animals to disappear. These events happened about 447–444 million years ago, when the Ordovician gave way to the Silurian Period. Many groups of sea animals were lost, including brachiopods, bryozoans, trilobites, conodonts, and graptolites.

Scientists think these changes happened because the Earth grew much colder, perhaps because there was less carbon dioxide in the air. This cold period caused large glaciers to form, which made the sea level drop. Many places where animals lived were lost, and it took a long time for life to grow back after the glaciers melted.