However the world’s first recognized mass extinction, which happened about 540 million years in the past, now seems to have had a extra delicate trigger: evolution itself.

Published Tuesday in Proceedings of the Royal Society B, Vanderbilt University scientists argue that Earth’s earliest single-celled organisms were largely wiped out after 3 billion years when new microorganisms evolved to capture the sun’s energy in a photosynthetic process.

Oxygen was poisonous to most microbes that had evolved in an oxygen-free environment, making it the world’s first pollutant. Oxygen gave them added energy that transformed them into mulitcellular beings called Ediacarans.

When these microorganisms began developing, that is where the problems started: The developed animals that started to eat the Ediacara left, causing the first mass extinction, scientists said. The rapid mass extinction that occurred 201 million years ago changed that.

Evolution usually allows animals to get better at avoiding death.

Most present day animal families, including vertebrates, molluscs, arthropods, annelids, sponges and jellyfish appeared during the 25 million year period of the Cambrian explosion.

These new behaviors, Darroch said, “fundamentally altered” the environment, and since the Ediacarans were “adapted to the environmental status-quo”, they wound up going extinct.

In this case, researchers analyzed the youngest known Ediacaran community that existed in Namibia almost 545 million years ago.

The team concluded that a combination of ecological stress, biological interactions and ecosystem engineering could have led to the Earth’s first mass extinction rather than a meteorite or a volcano.

Darroch and his colleagues made in depth efforts to make sure that the variations they recorded weren’t on account of some exterior issue.

For example, they ruled out the possibility that the Swartpunt site might have been lacking in some vital nutrients by closely comparing the geochemistry of the sites.

It’s a primary maxim in paleontology that the extra effort that’s made in investigating a given website, the larger the range of fossils that might be discovered there. So the researchers used statistical methods to compensate for the variation in the differences in the amount of effort that had been spent studying the different sites.