There have been several mass extinction events during the planet’s history, including the Cretaceous–Paleogene extinction event, arguably the best known because of the death of the dinosaurs. Now, researchers may have discovered a new mass extinction event, one that happened 2.05 billion years ago and likely killed between 80 percent and 99.5 percent of all of life on Earth.

In a study published in PNAS, a group of researchers looked at rocks in Hudson Bay, Canada, that formed billions of years ago and found that there was a sharp drop in life 2.05 billion years ago. This happened in conjunction with the end of the Great Oxidation Event (GOE), a period between 2.4 billion and 2 billion years ago that saw a surge and ultimately, a huge drop…