Dawn of the Carnivores: Biological Boom on Ancient Earth Linked to Oxygen

Millions of years ago, life was beginning to get a foothold on our planet. There was a veritable biological explosion of species as oxygen levels increased. Now, scientists have linked this animal boom to the rise of the carnivores on ancient Earth.

Understanding the past history of our planet is important for learning about how life emerged and, potentially, how it could emerge on other worlds. In order to examine a little bit more about ancient Earth, the researchers analyzed how low oxygen zones in modern oceans limited the abundance and types of carnivores that helped lead them to the cause of the "Cambrian radiation." This particular event was a historic proliferation of animals that occurred 500 to 540 million years ago that resulted in the animal diversity seen today.

"During the Cambrian period essentially every major animal body plan--from arthropods to mollusks to chordates, the phylum to which humans belong--appeared in the fossil record," said Erik Sperling of Harvard University in a news release.

In the study, the scientists examined modern oxygen gradients and their effects on marine worms. This allowed them to understand past evolutionary events. In the end, the researchers were able to link the proliferation of life seen in the Cambrian period to the evolution of carnivorous feeding modes. These animals needed higher oxygen concentrations to survive; once gas levels increased, animals started consuming other animals which, in turn, helped stimulate the Cambrian radiation through an escalatory predator-prey "arms race."

But the researchers aren't only just learning about the past of our Earth. The findings could also allow them to understand a little bit more about our future.

"The study of oxygen's role in the past is also going to help us understand the effects of and manage for changes in ocean oxygen in the future," said Lisa Levin, one of the researchers, in a news release. It's very possible that while an increase in oxygen in the past may have led to more species diversity, the current decreasing levels of oxygen we're seeing in the ocean could herald the opposite.

The findings are published in the journal Proceedings of the National Academy of Sciences.