A fossil-bearing block at South Africa’s Kromdraai cave now has its first absolute age constraints from uranium–lead dating. The selected estimates range from 1.94 to 2.67 million years, each with uncertainty. The peer-reviewed geochronology study supplies a framework for interpreting the cave’s fossil record by dating mineral formations associated with the deposit.
At Kromdraai cave in South Africa, mineral formations have supplied the first uranium–lead age constraints for a fossil-bearing block. The peer-reviewed investigation concerns KW 11000, a deposit within the UNESCO-listed Cradle of Humankind. It places the block between selected estimates of 1.94 million years, with uncertainty of 0.08 million years, and 2.67 million years, with uncertainty of 0.17 million years.[1]
The fossils themselves were not directly dated. Calcite already present before deposition supplies an older boundary; calcite that later filled cracks supplies a younger one. Including the stated uncertainties extends the overall bracket to 1.86–2.84 million years. This establishes a time frame for the deposit rather than one exact age for every fossil recovered from the cave.[1]
Different mathematical models accounted for variation in the samples’ initial uranium and lead compositions. The researchers assessed fit as well as precision, avoiding estimates whose narrow uncertainty could reflect an excessively close mathematical fit. Complementary dating could tighten the chronology. If hominin remains from the block become available, this framework could help examine whether different groups overlapped in time or occupied the landscape successively.[1]
