The clock was initially calibrated by dating objects of known age such as Egyptian mummies and bread from Pompeii; work that won Willard Libby the 1960 Nobel Prize in Chemistry.
The new date places Little Foot as an older relative of Lucy, a famous Australopithecus skeleton dated at 3.2 million years old that was found in Ethiopia.
It is thought that Australopithecus is an evolutionary ancestor to humans that lived between 2 million and 4 million years ago.
By analyzing the skeleton (which included hands, feet, limbs, pelvis, and skull), researchers estimate that she was about four feet tall and weighed about 110 pounds.
She was adept at both climbing through trees (with help from opposable big toes) as well as standing on two legs.
The technique hinges on carbon-14, a radioactive isotope of the element that, unlike other more stable forms of carbon, decays away at a steady rate.