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Extraterrestrial Cause for the Cretaceous-Tertiary Extinction

Alvarez, Luis W., Alvarez, Walter, Asaro, Frank, Michel, Helen V.·1980·Science
DOI 10.1126/science.208.4448.1095
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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 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 kilometers.

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Metadata

Authors
Alvarez, L. W., Alvarez, W., Asaro, F., & Michel, H. V.
Affiliations
  • Professor emeritus of physics at Lawrence Berkeley Laboratory, University of California, Berkeley 94720
  • Associate professor in the Department of Geology and Geophysics, University of California, Berkeley
  • Senior scientist in the Energy and Environment Division of Lawrence Berkeley Laboratory
  • Staff scientist in the Energy and Environment Division of Lawrence Berkeley Laboratory
Venue
Science
Publisher
American Association for the Advancement of Science (AAAS)
Published
1980-06-06
Volume
208
Issue
4448
Pages
1095-1108
ISSN
  • 0036-8075
  • 1095-9203
DOI
10.1126/science.208.4448.1095
Cited by
3,198
References
0
Language
en

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CoChat. (2026). Citation check: Extraterrestrial Cause for the Cretaceous-Tertiary Extinction. https://app.cochat.ai/papers/10.1126/science.208.4448.1095
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Alvarez, L. W., Alvarez, W., Asaro, F., & Michel, H. V. (1980). Extraterrestrial Cause for the Cretaceous-Tertiary Extinction. Science. https://doi.org/10.1126/science.208.4448.1095