Geochemistry, Geophysics, Geosystems
© 2014 American Geophysical Union
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Online ISSN: 1525-2027
Geomagnetic excursions date early hominid migration to China
Global-scale geomagnetic reversals, which are periods when the direction of Earth's magnetic field flips, leave imprints in magnetic minerals present in sediments. But so do smaller-scale, even local, changes in Earth's magnetic field direction. Paleomagnetists believe that the smaller-scale events represent 'failed reversals' and refer to them as 'geomagnetic excursions;' scientists use geomagnetic excursions in sedimentary basins as markers to tie together events of Earth's history across the globe. Ao et al. (2012) conducted high-resolution paleomagnetic measurements and mineralogical studies in paleolake sediments in the Nihewan Basin of northern China, which hosts two early hominid paleolithic sites, Feiliang and Lanpo. The authors identified a total of seven geomagnetic excursions between 1.6 and 0.8 million years before present, providing the best record of changes in Earth's magnetic field direction in the Northern Hemisphere around the Brunhes-Matuyama reversal, the last magnetic reversal that occurred 0.78 million years ago and hence one of the most important marker events in Earth's history. Seven of the nine excursions that the authors identified in the Nihewan Basin had not previously been well identified in any other terrestrial archive in China. By tying the large excursions to well-defined global reversal events and the smaller ones to more local excursion events that had been previously reported, the authors derived a timescale of hominid migration. Their geomagnetic timescale indicates that the paleolithic sites Feiliang and Lanpo are around 1.2 and 1.65 million years old, respectively, suggesting that early hominids migrated out of Africa and settled in northern China prior to 1.5 million years ago, long before the last major reversal took place on Earth.