Twenty years ago, a scientific team led by anthropologist Mary Leakey uncovered thousands of footprints, including tracks left by giraffes, elephants, rhinoceros and three hominids, at the edge of a gully eroded by the Ngarusi River. Scientists discovered the footprints on a mud walkway cured by deposits of volcanic ash. Radioactive dating showed the hominid footprints are more than three and-a-half million years old, suggesting that our oldest known ancestors left a soft-tissue record of what Leakey described as a 'slow, rolling gait'.

The Getty Conservation Institute and the government of Tanzania hired Masai tribesman like the one shown here to guard the walkway.
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