Extraterrestrial Cause for the Cretaceous-Tertiary Extinction

Bibliographic Data

ID23366397
AuthorsLuis W Alvarez (Professor emeritus of physics at Lawrence Berkeley Laboratory, University of California, Berkeley 94720), Walter Alvarez (0009-0002-6296-0528, Associate professor in the Department of Geology and Geophysics, University of California, Berkeley), Frank Asaro (Senior scientist in the Energy and Environment Division of Lawrence Berkeley Laboratory), Helen V Michel (Staff scientist in the Energy and Environment Division of Lawrence Berkeley Laboratory)
Year1980
Volume208
Issue4448
Pages1095-1108
Publication date1980-06-06
Peer ReviewedYes
Open AccessYes
TypeARTICLE
VenueScience (JOURNAL)
Journal identifiersISSN: 0036-8075 • E-ISSN: 0193-4511
PublisherAmerican Association for the Advancement of Science (AAAS) (PUBLISHER)
DOI10.1126/science.208.4448.1095
PMID17783054
OpenAlexW2110619496
LanguageEN
Citations received91
References cited46

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.

Abundance (ecology) · Asteroid · Astrobiology · Biological dispersal · Chondrite · Cretaceous · Earth science · Extinction (optical mineralogy) · Extinction event · Extraterrestrial life · Meteorite · Physics · Range (aeronautics) · Volcano · Astro and Planetary Science · Ecology · Geochemistry and Elemental Analysis · Geology · Geomagnetism and Paleomagnetism Studies · Paleontology

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