We often use the phrase ‘it’s the end of an era’ to signify some great change in our lives, like leaving school forever. But actual eras are far, far longer than our brains can comprehend, usually lasting several hundred million years, with dramatic, global ecological changes as their finale. Around 541 million years ago, there was such an ending. As the Neoproterozoic era came to a close, so did the Proterozoic eon, and nearly 3.5 billion years of bacterial rule. Suddenly the prokaryotic mats were breaking apart and the slow, soft-bodied organisms that characterised the late Neoproterozoic were dying. Following this mass extinction, the new Cambrian period brought stunning increases in the diversity and complexity of life. These increases are called the Cambrian explosion. But what caused such a striking shift?

This episode I will start with the fundamentals and work our way to the theorised explanations for the Cambrian explosion. I’ll explain how evolution works, summarise the great history of life on Earth, and outline the methods that scientists use to examine this history. Then I’ll draw our attention to the border between Ediacaran and Cambrian periods. We will see what was so significant about the evolutionary changes there, before assessing some of the most plausible reasons why the Cambrian explosion happened, and why it happened then of all times. 

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