From：National Geographic Writer：Jane J. Lee Date：2014-02-12
These ancient human footprints are direct evidence of the earliest known humans in Europe.
PHOTOGRAPH BY MARTIN BATES, BRITISH MUSEUM
As a group of ancient humans walked across a muddy beach in England nearly a million years ago, little did they know that one day, their footsteps would thrill modern discoverers.
The find—believed to be the oldest known human footprints found outside of Africa—wouldn't have happened without a rare combination of mud with just the right consistency, still or slow-flowing water, and a bit of perfect timing on the part of some modern humans.
"We found them by pure chance in May last year," writes Nicholas Ashton, a curator at the British Museum in London, in a blog post about the find. The footprints might help us understand how some of our early human predecessors made their way in the ancient world.
When Ashton and colleagues were at Happisburgh, a beach site in southeastern England, Martin Bates, an archeologist with Trinity Saint David University in Lampeter, Wales, noticed some hollowed-out holes in hardened sediments, located at the base of a cliff.
Bates thought they looked like footprints, so the researchers decided to investigate. They published their findings online February 7 in the journal PLOS ONE.
"We knew the sediments at Happisburgh were over 800,000 years old," says Ashton. So if the hollows turned out to be footprints, they would be older than anything outside of the cradle of humanity, Africa.
Race Against Time
Driving rain, incoming tides, and poor light hampered efforts to study the prints in the field. Eroding cliffs and relentless tides often uncover and then destroy archaeological sites in the area, so the scientists couldn't be sure how long the footprints would remain.
But Ashton and colleagues acquired a series of pictures of the footprints over a two-week period. The footprints were completely gone by the end of May.
They stitched the photographs together in a computer program to produce 3-D images of the site. That enabled the researchers to get length and width measurements of the footprints, and even to estimate the height and weight of the owners. Heights among the group topped out at 5.6 feet (1.7 meters) tall.
Twelve of the footprints were clear enough that Ashton and colleagues could determine that five individuals—likely a mix of older and younger individuals—left them behind. In one instance, the researchers could even make out toes.
The study authors were also able to determine that most of the footprints seemed to be traveling in a southerly direction along the ancient estuary.
Height estimates made from the footprints point to early humans known as Homo antecessor as the likely creators of these ancient tracks.
This species, also known as "Pioneer Man," lived in Europe and walked upright on two legs, Ashton explains. "They were smaller-brained than ourselves," he adds.
"We actually know very little else about the people who left these prints," Ashton says.