Biology
Scientific paper
Oct 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990sciam.263...78a&link_type=abstract
Scientific American (ISSN 0036-8733), vol. 263, Oct. 1990, p. 78-84.
Biology
10
Asteroids, Comets, Cretaceous-Tertiary Boundary, Meteorite Collisions, Paleobiology, Hypervelocity Impact, Iridium, Planetary Craters, Spherules
Scientific paper
Evidence suggesting that an asteroid or comet caused the Cretaceous extinction is presented. Study of the Cretaceous-Tertiary (KT) boundary reveals that extinction occurred at a relatively abrupt rate and that the presence of anomalous levels of iridium and of impact-generated (shocked) quartz crystals during this time period suggest a large impact. Basaltic spherules have also been found embedded in clays at the KT boundary at several locations and it is postulated that these spherules originated as molten droplets of ocean subfloor that were deposited globally by the KT impact. It is postulated that the impact of a 10 km asteroid travelling at 10 km per second would have dispersed shocked and molten materials around the globe by causing an explosion so powerful that the fireball would have sent entrained ejecta into orbit, eventually depositing them around the world. It is noted, however, that evidence of the 150-km crater that the impact of a 10 km object would have made has yet to be found.
Alvarez Walter
Asaro Frank
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