How long has our species walked on Earth? While there’s no conclusive answer to this question, scientists have previously dated the earliest human remains in East Africa to less than 200,000 years ago. Now, a new archaeological study has found that fossils of homo sapiens
emerged much earlier than previously known — at least 30,000 years earlier, to be exact.The earliest human fossils — known as Omo I — were originally discovered in the Omo Kibish Formation in southwestern Ethiopia in the late 1960s. The site is located in the East African Rift valley, an area where volcanic activity has preserved a large number of human remains, stone tools, and artifacts. Though they haven’t been able to determine the exact date of the fossils, scientists have long believed that they date back to under 200,000 years ago. But in a study published last week in the journal Nature, an international team of scientists led by the University of Cambridge says that the remains must be older than a massive volcanic eruption that took place at least 230,000 years ago.
The study is part of a four-year project to date all the major volcanic eruptions in the Ethiopian Rift. By dating these eruptions, the scientists believe they will be able to provide a more accurate timeline of the emergence of Homo sapiens, believed to have occurred in the area during the period known as the late Middle Pleistocene.
Earlier attempts to date the fossils have relied on a radiometric analysis of volcanic ash layers found above and below the sediments in which the remains were found. Scientists have not been able to use the same method with volcanic ash directly above Omo I because it was “too fine-grained,” according to Céline Vidal, a Cambridge geographer who led the study.
Using new techniques, Vidal and her team collected pumice rock samples from the same volcano and ground them down to “sub-millimeter” size to assess the age of their components. They sent the samples to peers at the University of Glasgow who found a geochemical match between the pumice and volcanic ash layers in the region aged more than 230,000 years.
“Each eruption has its own fingerprint
— its own evolutionary story below the surface, which is determined by the pathway the magma followed,” Vidal explained in a press release. “Once you’ve crushed the rock, you free the minerals within, and then you can date them, and identify the chemical signature of the volcanic glass that holds the minerals together.”Since the Omo I fossils were found in deeper sediments than the examined ash layers, the scientists say they must be more than 230,000 years old. And while they set a new “minimum age” for Homo sapiens in eastern Africa, they said that future discoveries may push the origins of the species further back in time.
“We can only date humanity based on the fossils that we have, so it’s impossible to say that this is the definitive age of our species,” said Vidal. “The study of human evolution is always in motion: boundaries and timelines change as our understanding improves. But these fossils show just how resilient humans are: that we survived, thrived and migrated in an area that was so prone to natural disasters.”
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