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Extraterrestrial cause for the Cretaceous-Tertiary extinction.

Title	Extraterrestrial cause for the Cretaceous-Tertiary extinction.
Authors	L W Alvarez, W Alvarez, F Asaro, H V Michel
Magazine	Science (New York, N.Y.)
Date	06/06/1980
DOI	10.1126/science.208.4448.1095
Introduction	Platinum group metals exhibit lower concentrations in the Earth's crust compared to their cosmic abundance. Elevated levels of these elements in deep-sea sediments can therefore signal the arrival of extraterrestrial matter. Analysis of deep-sea limestones from Italy, Denmark, and New Zealand reveals significant iridium enhancements—approximately 30, 160, and 20 times above baseline, respectively—coinciding precisely with the Cretaceous-Tertiary extinctions 65 million years ago. Evidence supports an extraterrestrial origin for this iridium, though it is not attributed to a proximate supernova. A theory correlates these extinctions with the iridium anomalies. The collision of a substantial Earth-crossing asteroid would propel roughly 60 times its mass as fragmented rock into the atmosphere. A portion of this atmospheric dust would persist in the stratosphere for several years, dispersing globally. The ensuing global dimming would inhibit photosynthesis, and the predicted biological repercussions align with the extinctions documented in the paleontological record. A key aspect of this theory has been confirmed: the boundary clay's chemical makeup, believed to derive from stratospheric dust, differs notably from the clay within the Cretaceous and Tertiary limestones, which themselves share similar chemical properties. Independent assessments estimate the asteroid's diameter to be approximately 10 ± 4 kilometres.
Quote	L W Alvarez, W Alvarez and F Asaro et al. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science (New York, N.Y.). 1980. Vol. 208(4448). DOI: 10.1126/science.208.4448.1095
Element	Iridium (Ir) , Platinum (Pt)
Materials	Chemical Compounds
Industry	Research & Laboratory , Space

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