End-Botomian mass extinction

The end-Botomian mass extinction event, also known as the late early Cambrian extinctions, took place during the early part of the Cambrian Period, about 513 to 509 million years ago. It included two separate periods when many kinds of ocean animals disappeared. Scientists think that up to 80% of all marine life at that time did not survive these events.

Many important groups of ancient sea creatures were greatly reduced or lost completely. These included the small shelly fossils, an early kind of tiny ocean animal; archaeocyathids, which were sponge-like animals; trilobites, famous sea arthropods with hard shells; brachiopods, animals that look like shells but are different from clams; hyoliths, unusual cone-shaped creatures; and early mollusks, a group that today includes snails and clams.

This extinction is important for understanding how life on Earth has changed over very long periods. By studying fossils from this time, scientists can learn about how ecosystems recover after big losses and what might cause such widespread disappearances of species.

Causes

Scientists have several ideas about why the end-Botomian mass extinction happened. One idea is that big changes in the carbon cycle and sea levels played a role. There's also evidence that some parts of the ocean lost oxygen, a condition called anoxia.

Another idea links these changes to huge volcanic eruptions from the Kalkarindji Large Igneous Province. These eruptions may have put lots of gases into the air, warming the climate and harming the oceans. Scientists found traces of mercury in rocks from this time, but they are still figuring out exactly how these events are connected.