mass extinctions

This week, the U.N. issued the summary of a report warning of unprecedented declines in biodiversity. Scott Simon makes the case for humankind to assume responsibility for protecting the vulnerable.

At various times, life on earth has come close to being erased. Paleontologist Peter Ward explains what we can learn from previous mass extinctions.

Scientists drilling beneath the Gulf of Mexico have hit the layer deposited when an asteroid the size of Staten Island, N.Y., hit Earth. Samples might contain details from that fateful day.