Silvia channelFrom Durham
Newly-uncovered fossils straight from the ground are one thing. Cenozoic Era, p. Because the hominid skulls and other artifacts found at Herto could not be directly dated—the organic material had long since been fossilized—the researchers instead performed their analysis on volcanic rock that was embedded in the sandstone near the fossils. The half-life of potassium is 1, million years, after which half of its substance will have changed into stable argon
Journal of Archaeological Science, This is because new sediments are always laid down on top of sediments that have already been deposited. Using SIMS, Valley's team was able to tease apart the carbon from the carbon within each fossil and measure the ratio of the two compared to a known carbon isotope standard and a fossil-less section of the rock in which they were found.