To get a better sense of what a mass extinction might look like (and how we might survive it) let's explore the ones that have already happened. Hope you're sitting down because this is some pretty intense stuff.
As we mentioned earlier, we've had five big mass extinctions up to this point [source: Barnosky et al.]:
- The Ordovician event: ended 443 million years ago; killed about 86 percent of all species
- The Devonian event: ended 359 million years ago; killed about 75 percent of all species
- The Permian event: ended 251 million years ago; killed about 96 percent of all species
- The Triassic event: ended 200 million years ago; killed about 80 percent of all species
- The Cretaceous event: ended 65 million years ago; killed about 76 percent of all species
That's a lot of death. But what could create such mass devastation? The causes for these events read like the scariest apocalypse novel you could imagine. Volcanic eruptions, meteor impacts, global temperature swings, and changes in the composition of both the atmosphere and oceans are all to blame for one mass extinction or another. Even scarier: While most of these die-offs took place over thousands or even millions of years, the Cretaceous event may have wreaked its havoc in the span of mere months.
Take the Permian event, which is morbidly referred to as "The Great Dying." According to one explanation, this extinction began some 252 million years ago when Earth boasted one huge landmass known as Pangea [source: Natural History Museum of London]. Global temperatures were higher than ever, making the continent's interior desert intensely hot and dry. Life was barely hanging on.
Then, one of the largest volcanic eruptions in history began, covering huge swaths of land in lava and spewing massive clouds of ash and toxic gasses into the air. After a short period of acid rain and global cooling, the entire planet began to warm in a big way. Carbon dioxide from the volcanoes filled the atmosphere and created a greenhouse effect. After 160,000 to 2.8 million years of devastation (a long time by our standards, but not Earth's), 96 percent of all species were extinct [source: Barnosky et al., Natural History Museum of London].
Obviously, surviving a mass extinction won't be a walk in the park.