nature | The Younger Dryas (YD) impact hypothesis posits that fragments of a
large, disintegrating asteroid/comet struck North America, South
America, Europe, and western Asia ~12,800 years ago. Multiple
airbursts/impacts produced the YD boundary layer (YDB), depositing peak
concentrations of platinum, high-temperature spherules, meltglass, and
nanodiamonds, forming an isochronous datum at >50 sites across ~50
million km² of Earth’s surface. This proposed event triggered extensive
biomass burning, brief impact winter, YD climate change, and contributed
to extinctions of late Pleistocene megafauna. In the most extensive
investigation south of the equator, we report on a ~12,800-year-old
sequence at Pilauco, Chile (~40°S), that exhibits peak YD boundary
concentrations of platinum, gold, high-temperature iron- and
chromium-rich spherules, and native iron particles rarely found in
nature. A major peak in charcoal abundance marks an intense
biomass-burning episode, synchronous with dramatic changes in
vegetation, including a high-disturbance regime, seasonality in
precipitation, and warmer conditions. This is anti-phased with
northern-hemispheric cooling at the YD onset, whose rapidity suggests
atmospheric linkage. The sudden disappearance of megafaunal remains and
dung fungi in the YDB layer at Pilauco correlates with megafaunal
extinctions across the Americas. The Pilauco record appears consistent
with YDB impact evidence found at sites on four continents.
