Earth cooler (Image: Martin Shields)

THE birth of the US Appalachian mountain chain may have been behind a major ice age and a mass extinction.

The extinction event at the end of the Ordovician 450 million years ago was the second largest Earth has ever seen. It has long been believed that an ice age caused it, but no one knew what triggered the freeze.

Seth Young of Indiana University in Bloomington, and colleagues, believe two factors conspired to create the deep freeze. First, layers of lava show that climate-warming volcanic activity slowed down at this time. The second factor …