Relationship Found Between Ancient Climate Change and Mass Extinction

In the Late Ordovician Period of Earth's geologic history, about 450 million years ago, more than 75 percent of marine species perished and Earth scientists have been seeking to discover what caused the extinction. It was the second largest in Earth's history.
Now, using a new research method, investigators believe they are closer to finding an answer.

http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=118671&org=NSF