The shape and location of the crater indicate further causes of devastation in addition to the dust cloud. The asteroid landed right on the coast and would have caused gigantic , for which evidence has been found all around the coast of the Caribbean and eastern United States—marine sand in locations which were then inland, and vegetation debris and terrestrial rocks in marine sediments dated to the time of the impact. The asteroid landed in a bed of (calcium sulphate), which would have produced a vast sulphur dioxide . This would have further reduced the sunlight reaching the Earth's surface and then precipitated as acid rain, killing vegetation, plankton and organisms which build shells from calcium carbonate ( and ). The crater's shape suggests that the asteroid landed at an angle of 20° to 30° from horizontal and traveling north-west. This would have directed most of the blast and solid debris into the central part of what is now the United States. Most paleontologists now agree that an asteroid did hit the Earth about 65 Ma, but there is an ongoing dispute whether the impact was the sole cause of the extinctions.
Recognition of mass extinctions, linked stratigraphically withunusual geologic activity and geochemical features, has resulted in two competinghypotheses to explain mass extinctions. The impact hypothesis states that the earth hascollided with one or more asteroids, each collision raising a dust cloud which inducedsuch environmental changes that an abrupt global mass extinction occurred. The volcanichypothesis states that the mass extinctions have been caused by episodes of flood basaltvolcanism, producing global environmental changes. Under these conditions mass extinctionswould have occurred over longer periods of time, although still relatively abrupt on ageological timescale. A strong debate among advocates of the opposing viewpoints hasensued, with neither side able to convincingly disprove the other hypothesis. This is aninteresting example of scientific debate which helps to demonstrate the nature ofscientific inquiry. The focus on catastrophic activity may be useful in developing modelsof the worldwide flood described in the scriptures.
Clear evidence exists that sea levels fell in the final stage of the Cretaceous by more than at any other time in the era. In some rock layers from various parts of the world, the later ones are terrestrial; earlier ones represent shorelines and the earliest represent seabeds. These layers do not show the tilting and distortion associated with ; therefore, the likeliest explanation is a , that is, a buildout of sediment, but not necessarily a drop in sea level. No direct evidence exists for the cause of the regression, but the explanation which is currently accepted as the most likely is that the became less active and therefore sank under their own weight as sediment from uplifted orogenic belts filled in structural basins.
A very large structure in the sea floor off the west coast of India has recently been interpreted as a crater by some researchers. The potential , 450–600 km (280–370 mi) in diameter, would substantially exceed Chicxulub in size and has also been dated at about 65 mya, an age consistent with the K–T boundary. An impact at this site could have been the triggering event for the nearby Deccan Traps. However, this feature has not yet been accepted by the geologic community as an impact crater and may just be a sinkhole depression caused by salt withdrawal.
Several other craters also appear to have been formed about the time of the K–T boundary. This suggests the possibility of near simultaneous multiple impacts, perhaps from a fragmented asteroidal object, similar to the cometary impact with . Among these are the , a 24 km (15 mi) diameter impact crater in and the , a 20 km (12 mi) diameter impact crater in the Any other craters that might have formed in the would have been obscured by tectonic events like the relentless northward drift of Africa and India.
The discussion of mass extinctions and their possible causes shouldbe of great interest to creationists. Investigations of the nature of species changesthrough the stratigraphic column could lead to better understanding of the causes ofstratigraphic sorting of fossils. The stepwise character of extinctions might be theresult of different source areas and differential sorting by the waters of the flood. Oneobservation that may be useful is that marine fossils trend from predominantly sessiletypes in Paleozoic sediments to more mobile types in Mesozoic sediments (Erwin 1989).Other ideas to investigate include stratigraphic trends in paleobiogeographicrelationships, lithologies, and paleocurrents.
Discussions of the possible effects of volcanism and meteoric impactsare also of interest to creationists. Large volcanic flows (Rampino and Stothers 1988) andnumerous craters apparently caused by extraterrestrial impacts (Napier and Clube 1979,Grieve 1990) are found within the layers of the stratigraphic column, indicating theiroccurrence during the accumulation of the sediments. The occurrence of all or most ofthese events within the relatively short period of the biblical flood implies acatastrophe of unprecedented magnitude. Despite this, few creationists have seriouslystudied the possibility of events as catastrophic as those currently being discussed inthe evolutionary community. The possibility that a large extraterrestrial impact was animportant energy source for the break-up of the earth's crust and release of the"fountains of the deep" that occurred during the flood should be considered.
The present discussion should not be interpreted as demonstrating thevalidity of the biblical flood story. However, although geologists generally take greatcare to emphasize that they do not accept the story of the biblical flood, the currentdiscussion of the geological and paleontological evidence seem to enhance therespectability of such a worldwide catastrophe. More importantly, the on-going debateprovides new data and new ideas that creationists may be able to utilize in developing abetter understanding of processes that may have occurred during the flood.
Global may have resulted as incendiary fragments from the blast fell back to Earth. Analyses of in ancient suggest that the content of the atmosphere was very high (30–35%) during the late Cretaceous. This high O2 level would have supported intense combustion. The level of atmospheric O2 plummeted in the early Tertiary Period. If widespread fires occurred, they would have increased the CO2 content of the atmosphere and caused a temporary once the dust cloud settled, and this would have exterminated the most vulnerable survivors of the "long winter".
The obvious consequence of an impact would be a dust cloud which would block and inhibit photosynthesis for a few years. This would account for the extinction of and and of dependent on them (including as well as ). However, small creatures whose food chains were based on might have still had a reasonable chance of survival. It is estimated that were injected into the , leading to a 10–20% reduction in sunlight reaching the Earth's surface. It would have taken at least ten years for those aerosols to dissipate.
The impact may also have produced , depending on what type of rock the asteroid struck. However, recent research suggests this effect was relatively minor. would have limited the changes, and the survival of animals vulnerable to effects (such as ) indicates that this was not a major contributor to extinction. Impact theories can only explain very rapid extinctions, since the dust clouds and possible sulphuric aerosols would wash out of the atmosphere in a fairly short time—possibly under ten years.
Smit, J., Montanari, A., Swinburne, N. H. M., Alvarez, W., Hildebrand,A., Margolis, S. V., Claeys, P., Lowrie, W. and Asaro, F., 1992. Tektitebearing deep-water clastic unit at the Cretaceous-Tertiary boundary in northeasternMexico. Geology, 20: 99-103.
Subsequent research, however, identified the buried under on the coast of , as the impact crater which matched the Alvarez hypothesis dating. Identified in 1990 based on the work of Glen Penfield done in 1978, this crater is oval, with an average diameter of about 180 kilometres (110 mi), about the size calculated by the Alvarez team.
Benton, M. J. and Little, C. T. S., 1994. Impact in the Caribbean anddeath of the dinosaurs, in Geology Today. Nov-Dec 1994. p. 222-227.