From the Ordovician period to present day where we may be experiencing a sixth mass extinction, here are the mass extinctions that repeatedly wiped out life on Earth.
Synapsids, such as this dinogorgon from South Africa's Karoo Basin, were nearly wiped out 251 million years ago during the End-Permian mass extinction. (Credit: Jonathan Blair/National Geographic Creative) Sign up for our email newsletter for the latest science news Congratulations, you're part of the 1 percent. That is, the 1 percent of species on Earth not yet extinct: For the last 3.5 billion or so years, about 99 percent of the estimated 4 billion species that ever evolved are no longer around. Many evolutionary family trees got the ax, so to speak, during a mass extinction. These events are defined as the loss of least 75 percent of species in the geological blink of an eye — which can range from thousands to millions of years. Researchers have enough data from the fossil record going back just over half a billion years to identify five such mass extinction events, and many scientists believe we're in the middle of a sixth. Great die-offs result from a perfect storm of multiple calamities, such as ocean acidification coupled with a spike in land temperatures. While the catalysts of these events are sometimes unclear, large-scale volcanic activity, spread across an entire region, is a usual suspect. Theories that asteroid strikes initiate the massive die-offs remain largely speculative: Only one space rock has been conclusively linked to a mass extinction. Each mass extinction ended a geologic period — that's why researchers refer to them by names such as End-Cretaceous. But it's not all bad news: Mass extinctions topple ecological hierarchies, and in that vacuum, surviving species often thrive, exploding in diversity and territory. 1. End-Ordovician: The 1-2 Punch Trilobites (foreground) got their start more than 520 million years ago, but faced their first decline during the End-Ordovician mass extinction. (Credit: Esteban De Armas/Alamy Stock Photo) When: About 443 million years ago Why: In the first pulse of a double whammy, ice sheets advanced,…