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More than 99 percent of all organisms that have ever lived on Earth are extinct. As new species evolve to fit ever changing ecological niches, older species fade away. But the rate of extinction is far from constant. At least a handful of times in the last 500 million years, 75 to more than 90 percent of all species on Earth have disappeared in a geological blink of an eye in catastrophes we call mass extinctions.
Though mass extinctions are deadly events, they open up the planet for new forms of life to emerge. The most studied mass extinction, which marked the boundary between the Cretaceous and Paleogene periods about 66 million years ago, killed off the nonavian dinosaurs and made room for mammals and birds to rapidly diversify and evolve.
Though the Cretaceous-Paleogene extinction is famous for being caused mainly by a huge asteroid, it’s the exception. The single biggest driver of mass extinctions appears to be major changes in Earth’s carbon cycle such as large igneous province eruptions, huge volcanoes that flooded hundreds of thousands of square miles with lava. These eruptions ejected massive amounts of heat-trapping gases such as carbon dioxide into the atmosphere, enabling runaway global warming and related effects such as ocean acidification and anoxia, a loss of dissolved oxygen in water.
Ordovician-Silurian extinction - 444 million years ago
The Ordovician period, from 485 to 444 million years ago, was a time of dramatic changes for life on Earth. Over a 30-million-year stretch, species diversity...
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