The researchers dated mineral crystals in volcanic ash layers above and below layers of river sediments that contain the early human bones. They conclude the fossils are much older than a 104,000-year-old volcanic layer and very close in age to a 196,000-year-old layer, says Brown. “These are the oldest well-dated fossils of modern humans (Homo sapiens) currently known anywhere in the world,” the scientists say in a summary of the study