Jeff Hecht in New Scientist:
Modern humans made their appearance 35,000 years earlier than we previously thought. According to new dates for two fossils found in Ethiopia almost 40 years ago, we have been around for 195,000 years.
The skulls were discovered along the Omo River in 1967 by anthropologist Richard Leakey and his team and were originally thought to be 130,000 years old.
At the time, other researchers doubted they were older than just 100,000 years. But modern radiometric and geological techniques now show that Leakey’s date was actually an underestimate.
The scientists, led by Ian McDougall at the Australian National University in Canberra, used a different dating approach for two types of material found with the skulls. Argon/argon radiometric dating was carried out on volcanic ash layers, while the analysis of other sedimentary layers provided further data.
They found that the sediments had collected only during relatively brief eras of extremely heavy monsoons – lasting about 1000 years in a 40,000-year cycle. This allowed the team to pin down the skulls’ age to within a short interval in geological time.