Long before the dinosaurs, a bleak environment of widespread fires and oxygen-poor coastal seawater killed off some 90 percent of all Earth's living species. The whole process took less than 200,000 years, according to a new study of the planet's most catastrophic mass-extinction event.

The end-Permian extinction probably isn't as well known as the Cretaceous extinction that wiped out the dinosaurs some 65 million years ago. But the end-Permian collapse nearly spelled the end of life on Earth.

Now scientists have painted a picture of just how fast the "Great Dying" unfolded 252 million years ago (prehistoric time line).

While the causes of the Permian extinction remain a mystery, from here on out, any theory must be compatible with a 200,000-year time frame centered around 252.28 million years ago, the authors assert. This time span is span indicated by analysis of fossils and chemical evidence of changes in Earth's carbon cycle in rocks from southern China to Tibet....