Great extinction came in phases
The greatest mass extinction recorded in Earth history did not occur as a result of one single cataclysmic event. A joint UK-Chinese team tell Nature magazine the disaster that befell the planet 250 million years ago must have happened in phases. Their conclusion is based on the abundance of "organic fossils" found in rocks at Meishan in southern China. These suggest there were at least two episodes to the mass die-off that saw up to 95% of lifeforms disappear.