(Table 1) Element analyses of DSDP Hole 15-149

An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the anomaly associated with the Cretaceous-Tertiary boundary. Other workers have deduced that the microtektites are part of the North American strewn tektite field, which is dated at about 34 million years before present, and that the microtektite horizon in deep-sea cores is synchronous with the extinction of five radiolarian species. Mass extinctions also occur in terrestrial mammals within 4 million years of this time. The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago.

在加勒比海深海钻探计划（Deep Sea Drilling Project）149号站位的岩芯中，发现铱异常（iridium anomaly）与已知微玻陨石（microtektite）层位恰好重合。该铱元素大概率并非赋存于微玻陨石内部，而是与微玻陨石同时沉积；若铱元素源自天体撞击形成的尘埃云并由此沉积，则可解释这一现象，正如白垩纪-古近纪界线（Cretaceous-Tertiary boundary）相关异常的既有研究假说所示。其他研究者推断，这些微玻陨石属于北美玻陨石散布场（North American strewn tektite field）的组成部分，其形成年代可追溯至距今约3400万年前；同时深海岩芯中的微玻陨石层位，与5种放射虫（radiolarian）物种的灭绝事件同步。在该时段前后400万年范围内，陆地哺乳动物也发生了大规模灭绝事件。铱异常、玻陨石与微玻陨石的发现，均支持距今约3400万年前曾发生过一次大型天体撞击事件。