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

年轻仙女木事件始于大约12,900年前，是北半球突然快速降温的时期，其主要原因尚不清楚。降温事件持续了大约1400年，它的开始与北美更新世大型动物群的突然灭绝和克洛维斯人的消失相吻合。普遍的假设机制是北美一座冰坝坍塌后，温盐循环暂时关闭。然而，最近的一篇论文提出，这种冷却是由多次彗星空爆和/或撞击引发的，这些爆炸和/或撞击导致了巨大的环境变化。支持这一假设的证据是在北美和欧洲的沉积物中有一个黑色的层，标志着年轻的仙女木边界。这一边界富含高含量的磁粒、磁性微球、纳米钻石和含有外星氦-3的富勒烯。影响假说正受到激烈辩论，因为尽管YD地平线显示出大范围森林火灾的证据，但它缺乏传统的影响标志。此外，磁球和含Ir的磁性颗粒的来源尚不清楚。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被烧毁的陆地颗粒，目前还有待最终证明。这项初步研究的目的是通过检查从Gainey(密歇根)、Murray Springs(亚利桑那州)和Lommel(比利时)适当区段分离的磁性物体中的Os(Os)同位素组成和Os和Ir浓度来检验撞击假说。此外，他们还将在伊利诺伊州水晶湖和马斯多登湖的高分辨率沉积物岩芯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.