Extinction: How Life on Earth Nearly Ended 250 Million Years Ago

Some 250 million years ago, the earth suffered the greatest biological crisis in its history. Around 95% of all living species died out--a global catastrophe far greater than the dinosaurs' demise 65 million years ago. How this happened remains a mystery. But there are many competing theories. Some blame huge volcanic eruptions that covered an area as large as the continental Unite More »