Web edition: February 22, 2013
Print edition: March 9, 2013; Vol.183 #5 (p. 4)
It has taken longer than previously credited for the kind of people now on earth to rise to become what we know as modern man. Evidence now is that man and his cultures extend beyond two million years into the past. Radioactive dating has given new time determinations for human ancestors and evolution in the dim anthropological past. The latest “clock” or dating method measures the amount of the chemical element argon in rocks to determine their age…. The date of the earliest skeletal remains, generally conceded “human,” those of Zinjanthropus discovered in Olduvai Gorge, Tanganyika, was found to be 1,750,000 years.