Opinion: Earth Has Survived Extinctions Before, It's Humans Who Are Fragile

Malcolm Hodgskiss, a Ph.D. candidate at Stanford and co-lead author of the study, says researchers found barite, an ancient mineral, in rocks in Canada's subarctic. The rocks have chemical signatures locked inside that help scientists determine what the Earth's atmosphere was like when they were formed.

Scientists say the Earth's only living inhabitants about 2 billion years ago were microorganisms. But when they photosynthesized, that process that turns light into chemical energy, the tiny organisms saturated the Earth with oxygen — too much oxygen. The excess essentially poisoned the atmosphere for 80 to 99.5% of the organisms that then thrived on Earth; and left the planet almost lifeless.

Malcolm Hodgskiss told CNN, "Even our most conservative estimates would exceed estimates for the amount of life that died off during the extinction of the dinosaurs approximately 65 million years ago."