The Cambrian period began a little over 500 million years ago. Before the Cambrian period, life on earth consisted of mostly single-celled organisms and bacteria. Afterwards the evolutionary ancestors of all the major groups of living things today were hanging around the planet. So what caused this evolutionary leap? According to one scientist, poop.
Biogeochemist Graham Logan published his opinion on the matter a few years ago. He points out that feces producing creatures, ones that ate food then excreted it like humans today, first arrived around 40 million years before the Cambrian period. He argued that their poo was what allowed oxygen levels to rise, and evolution to explode.
Before the advent of feces producing organisms, bacteria kept oxygen levels low. Plankton produced oxygen, but slowly. When they died, bacteria ate them and used most of the oxygen they produced to digest the dead plankton. This meant less oxygen for everyone else, and when you don’t have a lot of oxygen you’re apparently not going to be using all your energy on evolving into higher life forms.
Here’s where the feces creatures come in. Instead of bacteria eating the plankton bodies, these creatures, with their guts and what have you, would eat the plankton themselves. Then they’d excrete them. The excretions dropped to the ocean floor quickly and the bacteria starved. This meant lower bacteria populations, meaning they used less oxygen so everyone else had more.