Great Ordovician Biodiversification Event

The Great Ordovician Biodiversification Event (GOBE) was a time when many new kinds of sea animals appeared. This happened during the Ordovician period, about 40 million years after the Cambrian explosion.

Many new sea creatures came to live in the oceans. These included animals that could filter food from the water, called suspension feeder animals, and animals that lived freely in the open ocean, known as pelagic animals.

The GOBE happened after some periods when many sea animals had died out. These are called the Cambrian–Ordovician extinction events. After these events, the new animals that evolved stayed in the oceans for a very long time, throughout the Palaeozoic era. The number of different kinds of marine animals increased a lot.

This increase in animal life did not happen all at once or all over the world. It occurred at different times in different places. Natural factors, like changes in the Earth's climate and ocean chemistry, probably helped cause this burst of new life. Scientists think there isn't just one simple reason for the entire GOBE.

Duration

The Great Ordovician Biodiversification Event started about 497 million years ago and ended around 467 million years ago. It lasted for about 30 million years. It did not happen all at once. Different groups of animals appeared at different times during the Late Cambrian and Early and Middle Ordovician periods. Later, the rate at which new animals appeared slowed down. This was because animals became more specialized in certain areas and had less ability to move between different regions.

Causes

The Great Ordovician Biodiversification Event may have been caused by several things. More oxygen in the ocean might have helped animals grow. Changes in where the continents were and more volcanic activity could have added nutrients to the seas, helping more life.

Colder temperatures might also have helped, because cooler times often saw more new species. Some scientists think space rocks hitting Earth could have changed the climate, but this idea is still being talked about. All these changes made good conditions for many new sea species to evolve.

Main article: Great Ordovician Biodiversification Event

Tectonic activity

The moving of continents and lots of volcanic activity made a rich home for life. The Taconic orogeny helped bring important nutrients like iron and phosphorus to the oceans around Laurentia. As lands moved, they made many different homes, letting species change and grow apart. Reefs grew along the Baltican shelf as it moved into colder waters, and volcanoes may have added metals that helped life.

Global cooling

Colder temperatures may have helped more species develop. As the world cooled, more cold-water carbonates formed, which matches when many new fossils appeared. This cooling might have begun when extra carbon was buried, changing carbon in the world. The cooling in the middle to later Ordovician time is linked to a lot of new species appearing.

Oxygenation

Changes in thallium show that more oxygen came into deep and shallow waters during the latest Cambrian and earliest Ordovician. This extra oxygen likely helped start the big change in life. After a big change in carbon around 500 million years ago, the ocean’s changes made space for tiny plants that could make more oxygen. This oxygen helped more complex animals and worlds of life grow.

Extraterrestrial impacts

Some scientists think a space rock breaking apart could have caused Earth to be hit by many small rocks. This event, called the Ordovician meteor event, might have made dust clouds that blocked sunlight. Proof for this comes from finding extra helium-3 in ocean mud from that time. However, this may have happened after the main burst of new species, so it might not have helped start the change but could have slowed it down.

Positive feedbacks

Once the world started to help new species, they likely helped each other grow. As new species appeared, they made new jobs in the world of life, like different food chains or new homes for animals. Like the earlier Cambrian Explosion, changes in the world first helped tiny plants and animals in the water. This let more animals that eat plankton, like those on the sea floor or swimming freely, to grow and change.

Effects

The Great Ordovician Biodiversification Event helped add many new types of animals to the world. It was a big time of growth for life on Earth, making the oceans much more full of different kinds of creatures. Groups like brachiopods, gastropods, and bivalves became far more common.

Because the seas were warm and busy with life, tiny plants and animals called phytoplankton and zooplankton also grew in number. This helped many other sea animals, including those that eat by filtering water, to do well. The number of different animal groups grew a lot, and the kinds of species became much more varied, helping the oceans become rich and full of life.

Relationship to the Cambrian Explosion

Recent studies show that the Cambrian Explosion and the Great Ordovician Biodiversification Event (GOBE) were part of one big increase in marine life during the early Paleozoic period. Scientists used data from the Paleobiology Database and did not find strong reasons to separate these two events into different times.

Some scientists have mentioned a "Furongian Gap" between these two events, in the last part of the Cambrian period. But, it is not clear if this gap really existed or if it just looks that way because some fossils from that time are missing. Studies from places like the Guole Konservat–Lagerstätte in South China show that this time had many changes in plant and animal life.