On the edge of the western crater rim lies Olduvai Gorge, a location of significant archaeological discovery. Olduvai had been examined for many years, but following up on previous explorations, Dr Leakey and his wife (Mary) discovered early humanoid remains in 1959, after almost 3 decades of searching. The finds - 'Nutcracker Man' (Australopithecus) and 'Handy Man' (Homo habilis) dated man to have walked the earth 1.8 million years ago. This find, significant though it was, has been surpassed by Mary Leakey’s find nearby at Laetoli, 20 km to the north. The discovery of footprints, preserved in the volcanic ash of 3 humanoids (possibly a man, woman and child) walking upright has been dated to 3.5 million years ago. The Leakey's son, Richard (who has carved his own name is Kenyan environmental cicles) continued the work of his parents and has made similar significant discoveries in northern Kenya, in the Turkana region, that places early man in the region around 4 million years ago.