Cambrian–Ordovician extinction event

The Cambrian–Ordovician extinction event happened about 485 million years ago during the Paleozoic era in the early Phanerozoic eon. It marked the end of the Cambrian period and the start of the Ordovician period.

Many kinds of small sea animals did not survive this event. It greatly reduced the numbers of brachiopods, conodonts, and trilobite species. These changes helped shape the world’s oceans in the time that followed.

Causes

Scientists think that big volcanic eruptions might have caused changes in the environment that led to this extinction event. These eruptions happened around the same time as the event, but we do not know for sure if they were the reason for the changes in plant and animal life.

Other ideas include changes in the amount of oxygen in the water and shifts in how high or low the sea level was. During this time, many plants and animals were disappearing, possibly because the water did not have enough oxygen. Later, conditions changed again, which helped new kinds of life to grow and spread.

Effects on life

Trilobites were strongly affected by this extinction event. Those living in shallow waters suffered the most, while those in deeper waters were less impacted. Many trilobites had special ways to survive in low-oxygen water, working together with tiny organisms that could use sulfur.

Controversy

Scientists found fossils in Morocco that look like animals from the Cambrian period, but these fossils are 20 million years newer than the time when many animals disappeared. In 2010, some researchers suggested that these findings show that Cambrian animals might have continued to live longer than we thought. They believe that the idea of a big disappearance of animals from the Cambrian to the Ordovician might be because we simply haven’t found the right rocks to look in yet. These special fossils from the Cambrian were only kept in places where conditions were just right for preserving soft bodies.