But i don't think it killed them all..................but it killed a significant porportion, and for the next, however long....................the changes in the atmosphere.........the different eco systems........for one, all the dust, debris, all the rotting carcasses, etc.............would have alterned stuff enough, that with the changes in plant life, the # of tricerletops,,,,,,,,,,,reduced by the event itself.......the t rex has less to eat.............less t rexes after said event........less mating..........less plants for triceretops to eat......less tricereptops.............changes in the atmosphere, the continous cooling off of the earth itself from 4.6 billion years ago........one thing led to another..........and then, all were gone........

Effects of impact[edit]

Such an impact would have inhibited photosynthesis by creating a dust cloud that blocked sunlight for up to a year, and by injecting sulfuric acid aerosols into thestratosphere, which might have reduced sunlight reaching the Earth's surface by 10–20%. It has been argued that it would take at least ten years for such aerosols to dissipate, which would account for the extinction of plants and phytoplankton, and of organisms dependent on them (including predatory animals as well asherbivores). Small creatures whose food chains were based on detritus would have a reasonable chance of survival.^[80][95] The consequences of reentry of ejecta into Earth's atmosphere would include a brief (hours long) but intense pulse of infrared radiation, killing exposed organisms.^[50] Global firestorms likely resulted from the heat pulse and the fall back to Earth of incendiary fragments from the blast. Recent research indicates that the global debris layer deposited by the impact contained enough soot to suggest that the entire terrestrial biosphere had burned.^[114] The high O
2 levels during the late Cretaceous would have supported intense combustion. The level of atmospheric O
2 plummeted in the early Cenozoic era. If widespread fires occurred, they would have increased the CO
2 content of the atmosphere and caused a temporary greenhouse effect once the dust cloud settled, and this would have exterminated the most vulnerable organisms that survived the period immediately after the impact.^[115]

The impact may also have produced acid rain, depending on what type of rock the asteroid struck. However, recent research suggests this effect was relatively minor, lasting for approximately 12 years.^[95] The acidity was neutralized by the environment, and the survival of animals vulnerable to acid rain effects (such as frogs) indicate this was not a major contributor to extinction. Impact theories can only explain very rapid extinctions, since the dust clouds and possible sulfuric aerosols would wash out of the atmosphere in a fairly short time—possibly within 10 years.^[116]

The shape and location of the crater indicate further causes of devastation in addition to the dust cloud. The asteroid landed in the ocean and would have causedmegatsunamis, for which evidence has been found in several locations in the Caribbean and eastern United States—marine sand in locations that 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 gypsum (calcium sulfate), which would have produced a vast sulfur dioxide aerosol. This would have further reduced the sunlight reaching the Earth's surface and then precipitated as acid rain, killing vegetation, plankton, and organisms that build shells from calcium carbonate (coccolithophores and molluscs). In February 2008, a team of researchers used seismic images of the crater to determine that the impactor landed in deeper water than was previously assumed. They argued that this would have resulted in increased sulfate aerosols in the atmosphere, which could have made the impact deadlier by altering climate and by generating acid rain.^[117]

Most paleontologists now agree that an asteroid did hit the Earth at approximately the end of the Cretaceous, but there is an ongoing dispute whether the impact was the sole cause of the extinctions.^[36][118] There is evidence that there was an interval of about 300 ka from the impact to the mass extinction.^[119] In 1997, paleontologist Sankar Chatterjee drew attention to the proposed and much larger 600 km (370 mi) Shiva crater and the possibility of a multiple-impact scenario.

In March 2010 an international panel of scientists endorsed the asteroid hypothesis, specifically the Chicxulub impact, as being the cause of the extinction. A team of 41 scientists reviewed 20 years of scientific literature and in so doing also ruled out other theories such as massive volcanism. They had determined that a 10-to-15-kilometre (6.2 to 9.3 mi) space rock hurtled into Earth at Chicxulub on Mexico's Yucatán Peninsula. The collision would have released the same energy as 100 teratonnes of TNT (420 ZJ), over a billion times the energy of the atomic bombings of Hiroshima and Nagasaki.^[7]

Alternative hypotheses[edit]

The fact that the extinctions occur at the same time as the Chicxulub asteroid impact strongly supports the impact hypothesis of extinction. However, some scientists continue to dispute the role of the Chicxulub impact in driving the extinction, and to suggest that other events may have contributed to the end-Cretaceous mass extinction. In particular, volcanic eruptions, climate change, sea level change, and other impact events have been suggested to play a role in driving the K–Pg extinction.