A new discovery in the ongoing quest to determine when our human ancestors migrated out of Africa has shifted the timeline back – once again.
Writing in Nature, a team of geologists, archaeologists, and paleoanthropologists describe a rich cache of stone tools unearthed from a steep hillside in the Loess Plateau of north-central China. The 96 shaped flakes and unmodified hammerstones were found in 17 distinct sediment layers that date from 2.12 to 1.26 million years ago (Ma), providing evidence that a species of hominin – the lineage of bipedal humans that includes our genus, Homo, and its extinct ancient relatives – had settled in the region about 400,000 years earlier than previously collected fossils and tools indicate.
“Until now, the oldest known hominin site outside Africa was in Dmanisi, Georgia. Excavations at that site uncovered spectacular finds of the roughly 1.85 million- to 1.78-million-year-old remains of multiple hominins and stone tools,” wrote John Kappelman, a biological anthropologist and geologist at the University of Texas, in an accompanying article. A variety of other sites across western Europe to eastern Asia have confirmed that diverse populations of humans were established shortly after the Dmanisi settlement.
In an email to IFLScience, Professor Kappelman explained the significance of the findings made by lead author Zhaoyu Zhu and his colleagues: “[T]here was previous evidence for early hominins outside of Africa and across Asia at less than 2 million years ago. This new work moves the date back in time but more importantly shows that the dispersal was widespread across Asia.”
Zhu’s team dug at the picturesque Shangchen site for over a decade (2004 to 2017), uncovering the wealth of stones as well as bone fragments from antelope, deer, and pig family animals – though these have not been analyzed for signs of butchering. During the careful extraction process, the research group documented where in the fossilized layers of silt and soil each item lay, then examined the magnetic polarity of the sediment minerals in each layer. Because the dates of Earth’s many magnetic field reversals during the past 5 million or so years have been determined, the age of the sediment can be estimated by comparing the preserved polarity of the charged minerals within to a reference called the geomagnetic polarity timescale (GPTS).