Finding and dating the bones
Excavating in the dark Silberberg Grotto at Sterkfontein, millimetre by millimetre, year after year, to expose, identify and analyse the fragile bones of the ancient Little Foot skeleton embedded in the concrete-hard breccia is daunting work.
An understanding of what happened to the body during its long burial and what happened to the cave in which it lay, says Ron Clarke, suggests where the team may find the missing pieces of the skeleton and how old it might be.
After the first exciting finds, months of careful excavation had yielded little success, he recalls.
“We just had to keep looking.
Two lower legs next to each other without the rest of the body wasnâ€™t possible. Only when I noticed a cavity and an anomaly in the position of the flowstone, or stalagmitic rock, that looked like a fault, did I think, ‘Thatâ€™s strange. I wonder if another part of the skeleton went down and was sealed in by the flowstone deposited in a thin sheet by a flow water of water.â€™
“So we dug through it and one day Stephen Motsumiâ€™s chisel struck bone.”
When Little Footâ€™s body was deposited, concludes Clarke from his most recent excavations, it possibly rolled at least some way down the steep slope within the cavern and was partially mummified, which implies dry conditions at the time. The long, wet period that followed partially calcified the deposit around the bones.
It also resulted in water flowing through the breccia, or sediment and rock fragments cemented together by lime, creating a shallow cavity parallel to the slope.
Later, a portion of the breccia above this cavity that enclosed the middle part of the skeleton slumped into the cavity. A slow build-up of flowstone rock sealed the upper and middle part of the body, and filled the portion of the cavity underneath the lower leg bones.
That explains why the upper part of Little Foot was found beneath the thick flowstone, though the lower legs and feet were above it.
Tim Partridge, a professor with the Wits Climatology Research Group, confirms categorically that “Little Foot is certainly not younger than our original date estimate of between 3,22-million and 3,58-million years ago”.
He says that conclusive evidence from radiometric dating of the adjacent deposits will soon be published in an international scientific journal.
The recent much-publicised revised age estimates claimed by Lee Berger of Wits were, as Partridge has demonstrated in the South African Journal of Science, “based largely on outdated information and are therefore helpful neither to an understanding of hominid phylogeny nor of human origins.”