The New York Times reports
Paleontologists estimate that before the global spread of humankind the average rate of species extinction was one species per million in each one- to 10-million-year interval. Human activity has driven up the average global rate of extinction to 100 to 1,000 times that baseline rate.
The most striking fact about the living environment may be how little we know about it. Even the number of living species can be only roughly calculated. A widely accepted estimate by scientists puts the number at about 10 million. In contrast, those formally described, classified and given two-part Latinized names (Homo sapiens for humans, for example) number slightly more than two million. With only about 20 percent of its species known and 80 percent undiscovered, it is fair to call Earth a little-known planet.
Read full story The 8 Million Species We Don’t Know – The New York Times