all of my colleagues are alarmed. >> the alarm urlich sounded in '68 warned that overpopulation wouldidespread famine. he was wro about that. the green revolution fed the world. but he also wrote in '68 that heat from greenhouse gases would melt polar ice, and humanity would overwhelm the wild. today, humans have taken over 70% of the planet's land and 70% of the fresh water. >> the rate of extinction is extraordinarily high now and getting higher all the time. >> reporter: we know the rate of extinction is extraordinarily high because of a study of the fossil record by biologist tony barnovski, urlich's stanford colleague. >> the data are rock solid. i don't think you'll find a scientist that will say we're not in an extinction crisis. >> reporter: barnovski's research suggests that today's rate of extinction is up to 100 times faster than is typical in in the nearly 4 billion year history of life. these peaks represent the few times that life collapsed globally and the last was the dinosaurs, 66 million years ago. >> there are five times in earth's history where we had mass extincti