En 1976 Mary Leakey discovers the Laetoli footprints
During 1974 and 1975, the team led by Mary Leakey found in Laetoli, Tanzania, south of Olduvai Gorge, some hominid fossils and other animals fossils such as shrews, elephants and turtles. These deposits dated between 3.59 and 3.77 million years ago, the period when our bipedal ancestors consolidated their presence in the Great Rift Valley. When two co-workers found animal footprints preserved in solidified volcanic ashes, the team decided that since the site promised many surprises, it should be carefully studied.
The conservation of the Laetoli footprints is due to a combination of events. A series of volcanic eruptions coincided with some rain. The animals walked on the wet ashes, leaving footprints that solidified like cement when sun dried. The following eruption left a protective layer over the tracks. Currently there are six different layers 15 cm thick and containing well-preserved footprints.
In 1978 the team found the footprints of what appeared to be the heel of a hominid. The leaders designated Tim White in charge of the excavation of the site. Behind the heel, another footprint 20 cm long emerged. It was a print apparently made by a right foot. Behind it, the print of a left foot; behind that, another right foot; and so on. In summary, two trails 27.5 m long left by two individuals were the surprise the site had to offer. They are 3.6 million years old but very much like the prints we would leave after walking on wet sand.
These footprints are human, much like ours. The hominids walked in an upright position, moving away from the volcanoes. Although it may never be possible to assure which species they belong to, the consensus is that these tracks were left by some Australopithecus afarensis.