Roughly 500 million years ago, during the Cambrian period, life on Earth went from a few simple life forms to a truly astonishing variety of complex creatures. That’s when most of the animal groups we know today emerged. This event is known as the Cambrian explosion. (That scientists use the term “explosion” to describe something that unfolded over the course of 20 million years, give or take, tells you a lot about the unimaginably long periods of Earth’s history.)

Before the Cambrian, life forms were simple, and most of them lived in the sea. But suddenly (in evolutionary terms) animals evolved most of the organs and structural features they have today: legs, eyes, teeth, rudimentary backbones, etc. And they made their way to land.

But what caused this sudden explosion of life? No one knows for sure, but for a long time smart money has been on the oxygen theory: Increases in the level of oxygen in the ocean made many more life forms possible, and some of them moved from sea to land and went forth and multiplied.

However, a paper published this month argues for a different cause: poop. (Bet you were wondering if I was going to get around to that.) The research took a close look at poop in the fossil record and found that in the early part of the Cambrian some animals developed intestines, and of course, that led directly to poop. As digestive systems became more complex, the poop piled up. And to simplify things quite a bit, that meant more organic matter and nutrients (fertilizer) to feed more up-and-coming life forms. So, when the poop hit the fan — or waves, as it were — life took off.

It’s a fun study, but it’s worth keeping in mind that, as Erik Sperling, a scientist at Stanford University who studies this period in Earth’s history, told me, “There are about as many hypotheses out there for what caused the Cambrian explosion as there are fields of research.” So, I guess, if you’re a poop researcher, everything looks like poop?

’til next time,

Avery

PS — Fossilized pieces of poop are called coprolites. I hope that comes in handy on your next trivia night.

Image courtesy Alexas_Fotos via Pixabay