"Researchers used the new survey of the Messak Settafet to estimate that enough stone tools were discarded over the course of human evolution in Africa to build more than one Great Pyramid for every square kilometer of land on the continent."
Link: http://www.cam.ac.uk/research/news/saharan-carpet-of-tools-is-the-earliest-known-man-made-landscape
And I get discouraged because I can't find a single Arrowhead. No wonder.