A Test for the Extraterrestrial Origin of the Magnetic Spherules/Grains at the Younger Dryas Boundary

新仙女木事件（YD）开始于大约12，900年前，是北方半球突然和快速冷却的时期，其主要原因尚不清楚。冷却事件持续约1400年，其开始与突然更新世巨型动物灭绝和北美克洛维斯人的消失相吻合。流行的假设机制是北美冰坝破裂后温盐环流暂时关闭。然而，最近的一篇论文提出，冷却是由多次彗星空中爆炸和/或造成巨大环境变化的撞击引发的。支持这一假设的证据是北美和欧洲沉积物中标志着新仙女木边界的黑色层。这一边界富含富含铱的磁性颗粒、磁性微球、纳米金刚石和含有地球外He-3的富勒烯。撞击假说正在激烈地争论，因为虽然YD地平线显示了大范围森林火灾的证据，但它缺乏传统的撞击标志。此外，磁性球粒和含铱磁性颗粒的起源仍不清楚。这些磁性颗粒是陨石碎片还是微陨石，或者只是在森林大火中烧焦的陆地颗粒，还有待最终证明。 这项试点研究的目的是检验撞击假设，方法是检查从Gainey（密歇根州）、Murray Springs（亚利桑那州）和洛梅尔（比利时）的适当部分分离出来的磁性物体中的锇同位素组成以及锇和铱的浓度。此外，他们还将在伊利诺斯州水晶湖和乳齿象湖的高分辨率沉积物岩心中寻找陨石碎片的证据。

The Younger Dryas (YD) event, which began approximately 12,900 years ago, was a period of abrupt and rapid cooling in the Northern Hemisphere whose primary cause remains unclear. The cooling event is of ~1400 year duration and its onset coincides with abrupt Pleistocene megafaunal extinctions and the disappearance of the Clovis people in North America. The prevalent postulated mechanism has been a temporary shutdown of the thermohaline circulation following the breakup of an ice dam in North America. However, a recent paper proposes that the cooling was triggered by multiple cometary airbursts and/or impacts that engendered enormous environmental changes. The evidence in support of this hypothesis is a black layer marking the Younger Dryas boundary in sediments from North America and Europe. This boundary is enriched in magnetic grains high in iridium, magnetic microspherules, nanodiamonds, and fullerenes containing extra-terrestrial He-3. The impact hypothesis is being intensely debated for while the YD horizon shows evidence of extensive forest fires, it lacks traditional impact markers. Moreover, the origin of the magnetic spherules and iridium bearing magnetic grains remains unclear. It is yet to be demonstrated conclusively if these magnetic grains are meteorite debris or micrometeorites or just terrestrial grains singed in a forest fire. The purpose of this pilot study is to test the impact hypothesis by examining the osmium (Os) isotopic composition and osmium and iridium concentrations in magnetic objects separated from the appropriate sections at Gainey (Michigan), Murray Springs (Arizona) and Lommel (Belgium). Additionally, they will also look for evidence of meteorite debris in high resolution sediment cores from Crystal and Mastodon Lakes in Illinois.