Cretaceous-Tertiary impact

Pope K. O., Baines K. H., Ocampo A. C., and Ivanov B. A. (1997) Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact. J. Geophys. Res. 102, 21645-21664. 

The historical background is presented for the asteroid-impact theory that is based on the iridium anomaly found in rocks frm the Cretaceous-Tertiary boundary. Recent measurements of Ir, Pt, and Au abundances from such rocks in Denmark have shown that the element abundance ratios are different from mantle-derived sources and agree with values for chondritic meteorites within one standard deviation of the measurement errors (7-10%). Rare-earth patterns for these rocks are... 

There have been a number of suggestions in the past that an extraterrestrial object impacting on the. earth caused or could cause massive extinctions of life. E. J. Opik [11], for example, discussed the lethal effects which could be caused by the heat generated from such objects striking the earth, and H. C. Urey [12] stated specifically that a comet was probably the cause of the Cretaceous-Tertiary extinctions. There have also been science fiction stories and a movie relating to the effects. The events likely to occur if the sunlight were temporarily "turned off" have also been discussed [13]. Our deduction in contrast to the others is based on physical science data (the iridium anomaly) and is the only explanation we found which explained the Ir anomaloy could cause the massive extinction of life and was likely to occur in a period of 100 million years. 

Ganapathy, R., A Major Meteorite Impact on the Earth 65 Million Years Ago, Evidence from the Cretaceous-Tertiary Boundary Clay, Science 209, 921-923 (1980). 

Fullerenes are rather easily oxidized, which explains the fact that, despite their commonplace occurrence in soots, they had escaped detection for so long. Fullerenes have now been found in Precambrian carbonaceous rocks from Karelia, Russia in breccias associated with the 1.85-billion-year-old Sudbury impact structure in Canada and in a sooty layer (believed to be due to fires from the asteroid impact that is thought to have killed off the dinosaurs) marking the Cretaceous-Tertiary boundary in New Zealand.8... 

In recent years. Znller and associates University of Maryland) have studied six active volcanoes iAugustine, Mount St. Helens. El Chiehdn. Arcnal. Poas. and Colima) and have found no evidence of lr enrichment. The new Kilauea evidence of volcanic action as an Ir source tends to conflict with that of other researchers who have generally attributed the Ir anomaly to an extraterrestrial source, such as resulting from a cataclysmic meteorite or asteroid impact, notably in connection with (he Cretaceous-Tertiary [K i t boundary layer. 

Like iridium, arsenic is enriched in Cretaceous-Tertiary boundary shales from New Zealand (Brooks et al., 1984 Strong et al., 1987). The iridium is believed to have originated from an asteroid impact that caused the massive extinction at the end of the Cretaceous period about 65 million years ago. In contrast, most of the arsenic in the boundary shales probably had a terrestrial origin (Strong et al., 1987). The extinction of marine organisms, especially plankton, from the impact may have been responsible for increased anoxic conditions in the oceans, which led to the precipitation of arsenic in the marine deposits (Brooks et al., 1984), 541. 

Prinn R. and Fegley B. (1987) Bolide impacts, acid rain, and biospheric traumas at the Cretaceous-Tertiary boundary. Earth Planet. Sci. Lett. 83, 1-15. 

There are characteristic chemical properties of cosmic dust that have been involved in the study of sediment accumulation rates. The platinum group elements, such as iridium and osmium, offer good examples. Attempts to use iridium in this way have had the important result of indicating a giant meteorite impact at the Cretaceous-Tertiary boundary (Alvarez et ai, 1980) but it has not been proven important in determining chronometry. 

O Keefe J. D. and Ahrens T. J. (1989) Impact production of CO2 by the Cretaceous/Tertiary extinction bolide and the resultant heating of the Earth. Nature 338, 247-249. 

Pope K. O. (2002) Impact dust not the cause of the Cretaceous-Tertiary mass extinction. Geology 30, 99-102. 

The last globally catastrophic collision between Earth and an asteroid probably took place 65 million years ago at the end of the Cretaceous period. It now seems reasonably likely that the extinction of many species, including the great dinosaur extinction which occurred at the Cretaceous-Tertiary boundary, was caused by the impact of an asteroid approximately 6.2 mi (10 km) in diameter. The submerged remnants of the giant impact crater produced in this terminal Cretaceous collision were recently discovered on the coast of the Yucatan peninsula in Mexico. The crater, Chixulub (pronounced CHIKS-a-lub), is approximately 112 mi (180 km) in diameter and has long been buried under coastal sediments. 

H. Sigurdsson, S. D Hondt, and S. Carey, The impact of the Cretaceous/Tertiary bolide on evaporite terrane and generation of major sulphuric acid aerosol. Earth Planet. Sci. Lett 109, pp. 543-559 (1992). 

K.O. Pope, K.H. Baines, A.C. Ocampo, and B.A. Ivanov, hnpact winter and the Cretaceous/Tertiary extinctions results of a Chiexulub asteroid impact model. 

P.H. Schultz and S. D Hondt, Cretaceous-Tertiary (Chicxulub) impact angle and its consequences. Geology 24, pp. 963-967 (1996). 

Kundig W, Bonunel H, Constabaris G, Lindquist RH (1966) Some properties of supported small a-Fc203 particles determined with the Mossbauer effect. Phys Rev 142 327-333 Kyte FT (1998) A meteorite from the Cretaceous/Tertiary boundary. Nature 396 237-239 Kyte FT, Bohor BF (1995) Nickel-rich magnesiowiistite in Cretaceous/Tertiaiy boundary spherales crystallized from ultramafic, refractory sihcate liquids. Geochim Cosmochem Acta 59 4967-4974 Kyte FT, Bostwick JA (1995) Magnesiofenite spinel in Cretaceous/Tertiary boundary sediments of the Pacific basin Renmants of hot, early ejecta from the Chicxulub impact Earth Planet Sci Lett 132 113-127... 

Stishovite is a dense, meiastable polymorph of SiO with a C.N. = 6 for silicon. It forms at pressures above 8.5 GPa. In the meteoritic impact vs. vulcanism controversy over the nonconformity at the Cretaceous-Tertiary boundary ( What killed the dinosaurs ), the presence of stishovite at the K/T boundary has been used as an argument in favor of meteoritic impact rather than volcanic activity (See McHone, J. F. Nieman. R. A. Lewis. C. F. Yates, A. M. Science 1989. 243, 1182-1184). Discuss the possible changes involved in the quartz-to-stishoviic-" phase transitions in terms of heat and pressure, and how they relate to meteorites vs. volcanoes. (Sec also Sigurdsson, H. D Hondt. S. Arthur. M. A. Bralower, T. J. Zachos. J. C. van Fossen. M. Channcll, J. E. T. Nature, 1991. 349, 482-487.)... 

Perhaps the best known of the mass extinctions is that associated with the demise of the dinosaurs at the Cretaceous—Tertiary boundary, which has been attributed to a meteorite impact (Alvarez et al. 1980 Kruge et al. 1994 Skelton et al. 2003), although natural climate change may also have been a factor. Planktonic organisms (particularly foraminiferans, calcareous phytoplankton and radiolarians) were also severely affected. On land, trees seem to have been devastated, with the recovery period marked by the proliferation of ferns. The pollen record is dominated by fern spores, and hence known as the fern spike, which is observed... 

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