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.
