It may be surprising to learn that we really have no idea how many species exist on our planet. Many experts believe that the earth plays host to anywhere from 10 to 30 million species. A few say that number could be much higher. But by any reckoning, only a fraction of them are known to science. On this special edition of Living on Earth, Science Editor Diane Toomey visits with famed biologist E.O. Wilson. He's calling for an all-out effort to discover, describe and classify as many of them as they can before it's too late.