Geology Program, School of Earth Science and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011, USA.
Proc Natl Acad Sci U S A. 2012 Jul 10;109(28):E1903-12. doi: 10.1073/pnas.1204453109. Epub 2012 Jun 18.
It has been proposed that fragments of an asteroid or comet impacted Earth, deposited silica- and iron-rich microspherules and other proxies across several continents, and triggered the Younger Dryas cooling episode 12,900 years ago. Although many independent groups have confirmed the impact evidence, the hypothesis remains controversial because some groups have failed to do so. We examined sediment sequences from 18 dated Younger Dryas boundary (YDB) sites across three continents (North America, Europe, and Asia), spanning 12,000 km around nearly one-third of the planet. All sites display abundant microspherules in the YDB with none or few above and below. In addition, three sites (Abu Hureyra, Syria; Melrose, Pennsylvania; and Blackville, South Carolina) display vesicular, high-temperature, siliceous scoria-like objects, or SLOs, that match the spherules geochemically. We compared YDB objects with melt products from a known cosmic impact (Meteor Crater, Arizona) and from the 1945 Trinity nuclear airburst in Socorro, New Mexico, and found that all of these high-energy events produced material that is geochemically and morphologically comparable, including: (i) high-temperature, rapidly quenched microspherules and SLOs; (ii) corundum, mullite, and suessite (Fe(3)Si), a rare meteoritic mineral that forms under high temperatures; (iii) melted SiO(2) glass, or lechatelierite, with flow textures (or schlieren) that form at > 2,200 °C; and (iv) particles with features indicative of high-energy interparticle collisions. These results are inconsistent with anthropogenic, volcanic, authigenic, and cosmic materials, yet consistent with cosmic ejecta, supporting the hypothesis of extraterrestrial airbursts/impacts 12,900 years ago. The wide geographic distribution of SLOs is consistent with multiple impactors.
有人提出，小行星或彗星的碎片撞击地球，在几个大陆上沉积了富含硅和铁的微球和其他示踪剂，并引发了 12900 年前的新仙女木冷却事件。尽管许多独立的研究小组已经证实了撞击的证据，但该假说仍然存在争议，因为一些研究小组未能证实这一点。我们研究了跨越三大洲（北美洲、欧洲和亚洲）的 18 个有年代记录的新仙女木边界（YDB）地点的沉积序列，这些地点大致环绕地球的三分之一，跨度达 12000 公里。所有地点的 YDB 都显示出丰富的微球，而在上下方几乎没有微球。此外，三个地点（叙利亚的阿布胡赖拉、宾夕法尼亚州的梅洛罗斯和南卡罗来纳州的布莱克斯维尔）显示出具有气泡、高温、硅质火山渣状的物体，或 SLO，它们在地球化学上与微球相匹配。我们将 YDB 物体与已知的宇宙撞击（亚利桑那州的流星陨石坑）和 1945 年新墨西哥州索科罗的 Trinity 核爆炸的熔融产物进行了比较，发现所有这些高能事件产生的物质在地球化学和形态上都是相似的，包括：（i）高温、快速淬火的微球和 SLO；（ii）刚玉、莫来石和苏氏体（Fe(3)Si），一种罕见的陨石矿物，在高温下形成；（iii）熔融的二氧化硅玻璃，或柯石英，具有流纹（或条纹）纹理，在 >2200°C 时形成；以及（iv）具有高能量粒子间碰撞特征的颗粒。这些结果与人为、火山、自生和宇宙物质不一致，而与宇宙喷出物一致，支持了 12900 年前外星爆炸/撞击的假说。SLO 的广泛地理分布与多个撞击器一致。
