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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. Journal Information Science, founded by Thomas A. Edison in 1880 and published by AAAS, today ranks as the world's largest circulation general science journal. Published 51 times a year, Science is renowned for its highly cited, peer-reviewed research papers, its special strength in life science disciplines, and its award-winning coverage of breaking science news. The online edition includes not only the full text of current issues, but also Science archives dating back to Edison's first edition in 1880. Science Careers, found in print and online, provides relevant career articles published weekly, thousands of job postings updated several times a week, and other career related services. The online Science Multimedia Center features Science Podcasts, images and slide shows, videos, seminars, and other interactive features. For more information, access www.sciencemag.org. Publisher Information AAAS, founded in 1848, has evolved into the world's largest multidisciplinary scientific society with nearly 130,000 members and subscribers. The mission, to "advance science, engineering, and innovation throughout the world for the benefit of all people," has propelled the organization to the forefront of national and international initiatives. Global efforts include programs and partnerships worldwide, from Asia to Europe to Africa, and extensive work in human rights using geospatial technology to corroborate abuses. Science and policy programs include the major annual forum on Science & Technology policy, S&T policy fellowships within the US Congress and government agencies, and the tracking of US funding for R&D research. Science education initiatives have laid the groundwork for standards-based learning and provide web-based support tools for teachers. Public engagement activities are creating an open dialogue with scientists on societal issues such as global climate change. AAAS also acts as an umbrella organization for a federation of more than 270 affiliated scientific groups. An extended series of websites includes comprehensive career development resources. For more information, access www.aaas.org. Recommended textbook solutions Environmental Science for AP2nd EditionAndrew Friedland, Rick Relyea 965 solutions Applications and Investigations In Earth Science9th EditionDennis G. Tasa, Edward J. Tarbuck, Frederick K. Lutgens 1,295 solutions
Investigating Oceanography3rd EditionKeith A. Sverdrup, Raphael Kudela 547 solutions Environmental Science for AP3rd EditionAndrew Friedland, Rick Relyea 957 solutions What was the critical piece of evidence that supported the hypothesis that an asteroid?To test the hypothesis that an asteroid impact caused the K-T mass extinction, key evidence included impact ejecta, tsunami debris, and careful gravitational field measurements.
What was the critical piece of evidence that supported the hypothesis that an asteroid struck Earth 65 million years ago?What was the critical piece of evidence that supported the hypothesis that an asteroid struck Earth about 65 million years ago? The Chicxulub crater in Mexico.
Which piece of evidence definitely showed that an asteroid had struck Earth?Which piece of evidence definitely showed that an asteroid had struck Earth? Explain your answer. The crater at Chicxulub was the smoking gun. Finding a crater that matched the age and size of the asteroid provided direct evidence for the impact.
Which field of study contributed to the research that led to the impact hypothesis?Answer and Explanation: The fields of study that contributed to the research that led to the impact hypothesis are as follows: Biology.
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Which piece of evidence (a-g) lead scientists to dismiss the supernova hypothesis
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