how old is the lower layer of volcanic ash
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
USGS scientists recently released a report about the age of the youngest volcanic deposits at Eagle Lake, CA, in which they concluded that three of the most recent lava flows erupted 130, 127 and 123 thousand years ago.