RESUMO
The Younger Dryas (YD) abrupt cooling event ca. 12.9 ± 0.1 ka is associated with substantial meltwater input into the North Atlantic Ocean, reversing deglacial warming. One controversial and prevailing hypothesis is that a bolide impact or airburst is responsible for these environmental changes. Here, highly siderophile element (HSE; Os, Ir, Ru, Pt, Pd, and Re) abundances and 187Os/188Os ratios were obtained in a well-dated sediment section at Hall's Cave, TX, USA to test this hypothesis. In Hall's Cave, layers below, above, and in the YD have 187Os/188Os ratios consistent with incorporation of extraterrestrial or mantle-derived material. The HSE abundances indicate that these layers contain volcanic gas aerosols and not extraterrestrial materials. The most likely explanation is that episodic, distant volcanic emissions were deposited in Hall's Cave sediments. Coupled 187Os/188Os ratios and HSE concentration data at close stratigraphic intervals are required to effectively differentiate between bolide and volcanic origins.
RESUMO
Lower Paleolithic artifacts have been recovered from a single occupation surface within stratified deposits at Diring Yuriakh, an archaeological site in central Siberia. Thermoluminescence age estimates from eolian sediments indicate that the cultural horizon is greater than 260,000 years old. Diring Yuriakh is an order of magnitude older than documented Paleolithic sites in Siberia and is important for understanding the timing of human expansion into the far north, early adaptations to cold climates, and the peopling of the Americas.
