EXTRATERRESTRIAL CAUSE FOR THE CRETACEOUS-TERTIARY EXTINCTION - EXPERIMENTAL RESULTS AND THEORETICAL INTERPRETATION
EXTRATERRESTRIAL CAUSE FOR THE CRETACEOUS-TERTIARY EXTINCTION - EXPERIMENTAL RESULTS AND THEORETICAL INTERPRETATION
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DOI：
10.1126/science.208.4448.1095
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发表时间：
1980-01-01
期刊：
影响因子：
56.9
通讯作者：
MICHEL, HV
中科院分区：
文献类型：
--
作者：
ALVAREZ, LW;ALVAREZ, W;MICHEL, HV
铂金属在地壳中相对于它们的宇宙丰度是贫化的;深海沉积物中这些元素的浓度可能表明外星物质的流入。暴露在意大利、丹麦和新西兰的深海石灰岩显示，在6500万年前的白垩纪-第三纪沉积时期，Ir分别比背景水平高出约30、160和20倍。有理由表明这颗Ir是来自地球外的，但不是来自附近的超新星。提出了一个假设，其中占的precautions和Ir的意见。一颗穿越地球的大型小行星的撞击将把大约60倍于该物体质量的岩石粉末注入大气层;这些尘埃的一小部分将在平流层停留数年，并分布在世界各地。由此产生的黑暗会抑制光合作用，预期的生物后果与古生物学记录中观察到的结果非常吻合。这一假说的一个预测得到了验证：可能来自平流层尘埃的边界粘土的化学成分与化学成分相似的白垩纪和第三纪石灰岩混合粘土的化学成分明显不同。四个不同的独立估计的小行星的直径给出的值都在10 .+-。4公里
Pt metals are depleted in the earth''s crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may indicate influxes of extraterrestrial material. Deep sea limestones exposed in Italy, Denmark and New Zealand show Ir increases of about 30, 160 and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million yr ago. Reasons are given to indicate that this Ir is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is suggested which accounts for the extinctions and the Ir observations. Impact of a large earth-crossing asteroid would inject about 60 times the object''s mass into the atmosphere as pulverized rock; a fraction of this dust would stay in the stratosphere for several years and be distributed worldwide. The resulting darkness would suppress photosynthesis, and the expected biological consequences match quite closely the extinctions observed in the paleontological record. One prediction of this hypothesis was verified: the chemical composition of the boundary clay, which may come from the stratospheric dust, is markedly different from that of clay mixed with the Cretaceous and Tertiary limestones, which are chemically similar to each other. Four different independent estimates of the diameter of the asteroid give values that lie in the range 10 .+-. 4 km.