Great Ordovician Biodiversification Event

The Great Ordovician Biodiversification Event (GOBE) was an evolutionary radiation of marine animal life that happened during the Ordovician period, about 40 million years after the Cambrian explosion. During this time, many new kinds of sea creatures appeared, replacing the older groups that had lived during the Cambrian period. This new group of animals included many that were good at filtering food from the water, called suspension feeder animals, as well as those that lived freely in the open ocean, known as pelagic animals.

The GOBE happened after a few periods when many sea animals had died out, known as the Cambrian–Ordovician extinction events. After these events, the new animals that evolved stayed dominant in the oceans for a very long time, throughout the Palaeozoic era. The number of different kinds of marine animals increased a lot, reaching levels similar to what we see in the oceans today. The way these animals looked and lived also became more different and varied.

Interestingly, this big increase in animal life did not happen all at once or all over the world. It occurred at different times in different places. Many natural factors, like changes in the Earth's climate and ocean chemistry, probably worked together to cause this great burst of new life. Because of this complex mix of influences, scientists think there isn't just one simple reason that can explain the entire GOBE.

Duration

The Great Ordovician Biodiversification Event began around 497 million years ago and ended around 467 million years ago, lasting for about 30 million years. It wasn’t a single event but happened in stages, with different groups of animals diversifying at different times during the Late Cambrian and Early and Middle Ordovician periods. Later on, the rate of diversification slowed down due to factors like increased regional specialization and limited movement between different areas.

Causes

The Great Ordovician Biodiversification Event may have been caused by several factors. One idea is that more oxygen in the ocean helped animals thrive. Changes in the positions of the continents and increased volcanic activity could have brought more nutrients to the seas, supporting more life.

Cooler global temperatures might also have played a role, as cooler periods often saw more new species appear. Some scientists even suggest that space rocks hitting Earth could have affected the climate, though this idea is still debated. Together, these changes created perfect conditions for many new marine species to evolve and diversify.

Main article: Great Ordovician Biodiversification Event

Tectonic activity

The movement of continents and high levels of volcanic activity created a rich environment for life to grow. The Taconic orogeny helped bring important nutrients like iron and phosphorus into the oceans around Laurentia. As landmasses shifted, they created many different habitats, allowing species to adapt and evolve in isolation. Reefs grew along the Baltican shelf as it moved into cooler waters, and volcanic activity may have added trace metals that supported life.

Global cooling

Cooler temperatures may have encouraged more species to develop. As the climate cooled, more cool-water carbonates formed, which matches the time when many new fossils appeared. This cooling might have started when extra organic carbon was buried, leading to changes in carbon isotopes. The cooling in the middle to late Ordovician period is linked to a burst of new species appearing.

Oxygenation

Changes in thallium isotopes show that more oxygen became available in deep and shallow waters during the latest Cambrian and earliest Ordovician. This extra oxygen likely helped trigger the biodiversification. After a major change in carbon isotopes around 500 million years ago, the ocean’s extinction opened up new spaces for tiny plants that could produce more oxygen. This oxygen boost supported more complex animals and ecosystems.

Extraterrestrial impacts

Some scientists think that an asteroid breaking apart could have caused Earth to be hit by many meteorites. This event, called the Ordovician meteor event, might have created dust clouds that blocked sunlight. Evidence for this comes from finding extra helium-3 in ocean sediments from that time. However, this event may have happened after the main burst of new species, so it might not have helped cause the diversification but could have slowed it down instead.

Positive feedbacks

Once conditions started favoring new species, they likely helped each other grow. As new species appeared, they created new roles in the ecosystem, like different food chains or new homes for other animals. Like the earlier Cambrian Explosion, changes in the environment probably first boosted tiny plants and animals in the water. This allowed more animals that feed on plankton, like those on the sea floor or swimming freely, to thrive and diversify.

Effects

The Great Ordovician Biodiversification Event helped fill out many animal groups with new types of species. It was one of the biggest times of growth in the history of life on Earth, making the oceans much more diverse. Groups like brachiopods, gastropods, and bivalves became much more common.

Because the seas were warm and full of life, tiny plants and animals called phytoplankton and zooplankton also grew in number. This helped many other sea creatures, including animals that feed by filtering water, to thrive. The number of different animal groups doubled, and the variety of species tripled, making the oceans as rich and full of life as they are today.

Relationship to the Cambrian Explosion

Recent studies suggest that the Cambrian Explosion and the Great Ordovician Biodiversification Event (GOBE) were not two separate events, but part of one continuous increase in marine life during the early Paleozoic period. Researchers looked at data from the Paleobiology Database and found no strong evidence to split these two events into different times.

Some scientists have talked about a "Furongian Gap" between these two events, during the last part of the Cambrian period. However, it's not clear if this gap really existed or if it just seems 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 was actually very active with many changes in plant and animal life.