What proportion of all species that ever lived has become extinct?

a. less than 1 percent

c. more than 99 percent

b. approximately one-half

d. 100 percent?

More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described.