English: Cast of the "Laetoli footprints" -- the earliest known human footprints in the world, on display in the Hall of Human Origins in the Smithsonian Museum of Natural History in Washington, D.C.These footprints are those of Australopithecus afarensis. The entire footprint trail is 88 feet long and includes impressions left by two individuals. They were made 3.6 million years ago in Laetoli, Tanzania, when A. afarensis walked through wet volcanic ash. Paleontologist Mary Leakey found them in 1976, but they were not identified until Paul Abell did so in 1978. There are 70 footprints in total.