Physics
Scientific paper
Jun 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986sci...232.1225k&link_type=abstract
Science (ISSN 0036-8075), vol. 232, June 1986, p. 1225-1229.
Physics
95
Core Sampling, Extraterrestrial Matter, Geochemistry, Iridium, Comets, Neutron Activation Analysis, Ocean Bottom
Scientific paper
Iridium measured in 149 samples of a continuous 9-meter section of Pacific abyssal clay covering the time span 33 to 67 million years ago shows a well-defined peak only at the Cretaceous/Tertiary boundary. In the rest of the section iridium ranges from a minimum concentration near 0.35 nanograms per gram in the Paleocene to a maximum near 1.7 in the Eocene. Correction for terrestrial iridium leads to an extraterrestrical flux of 9±3 nanograms of iridium per square centimeter per million years, and an estimated annual global influx of 78 billion grams of chondritic matter, consistent with recent estimates of the influx of dust, meteorites, and crater-producing bodies with masses ranging from 10-13 to 1018grams. Periodic comet showers should increase the cometary iridium flux by a factor of 200 to 600 on a time scale of 1 to 3 million years; the predicted iridium maxima (more than 30 times background) are not present in the intervals associated with the Cretaceous/Tertiary boundary or the tektite-producing late Eocene events.
Kyte Frank T.
Wasson John T.
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