Extraterrestrial cause for the cretaceous-tertiary extinction
Abstract
Platinum metals are depleted in the earth's crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may thus indicate influxes of extraterrestrial material. Deep-sea limestones exposed in Italy, Denmark, and New Zealand show iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago. Reasons are given to indicate that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is suggested which accounts for the extinctions and the iridium 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 has been verified: the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of cla...Continue Reading
References
Citations
The synthesis of primitive 'living' forms: definitions, goals, strategies and evolution synthesizers
Platinum stable isotope analysis of geological standard reference materials by double-spike MC-ICPMS
Lower prevalence but similar fitness in a parasitic fungus at higher radiation levels near Chernobyl
Site of asteroid impact changed the history of life on Earth: the low probability of mass extinction
Asteroid shower on the Earth-Moon system immediately before the Cryogenian period revealed by KAGUYA
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