Dinosaurs were a very successful and diverse group, dominating the terrestrial environments of the earth for million years. The apparently sudden mass extinction of dinosaurs marks the boundary between the Cretaceous and Tertiary periods. The theories that explain their extinction at the end of the Cretaceous period are the asteroid, the volcanoes, and the major climatic changes. The most popular "disaster theory" for the extinction of the dinosaurs is that the Earth was hit by an asteroid or a comet 65 million years ago.
Timeline of Cretaceous-Paleogene extinction event research Ina team of researchers led by Nobel prize-winning physicist Luis Alvarezhis son, geologist Walter Alvarezand chemists Frank Asaro and Helen Vaughn Michel discovered that sedimentary layers found all over the world at the Cretaceous—Paleogene boundary K—Pg boundary, formerly called Cretaceous—Tertiary or K—T boundary contain a concentration of iridium hundreds of times greater than normal.
The Alvarez team suggested that an asteroid struck the earth at the time of the Cretaceous—Paleogene boundary. Kelly ] and Frank Dachille analyzed global geological evidence suggesting that one or more giant asteroids impacted the Earth, causing an angular shift in its axis, global floods, fire, atmospheric occlusion, and the extinction of the dinosaurs.
Chromium isotopic anomalies found in Cretaceous—Paleogene boundary sediments are similar to that of an asteroid or a comet composed of carbonaceous chondrites. Shocked quartz granules, glass spherules and tektitesindicative of an impact event, are common in the Cretaceous—Paleogene boundary, especially in deposits from around the Caribbean.
All of these constituents are embedded in a layer of clay, which the Alvarez team interpreted as the debris spread all over the world by the impact. Badlands near DrumhellerAlberta where erosion has exposed the K—Pg boundary.
Using estimates of the total amount of iridium in the K—Pg layer, and assuming that the asteroid contained the normal percentage of iridium found in chondritesthe Alvarez team went on to calculate the size of the asteroid. Paul Renne of the Berkeley Geochronology Center has reported that the date of the asteroid event is 66, years ago, plus or minus 11, years, based on the radioactive decay of argon.
He further posits that the mass extinction of dinosaurs occurred within 33, years of this date.
This would account for the extinction of plants and phytoplankton and of all organisms dependent on them including predatory animals as well as herbivores. But small creatures whose food chains were based on detritus would have a reasonable chance of survival.
It would have taken at least ten years for those aerosols to dissipate. This high O2 level would have supported intense combustion. The level of atmospheric O2 plummeted in the early Paleogene Period. The impact may also have produced acid raindepending on what type of rock the asteroid struck.
However, recent research suggests this effect was relatively minor. Chemical buffers would have limited the changes, and the survival of animals vulnerable to acid rain effects such as frogs indicate this was not a major contributor to extinction. Although further studies of the K—Pg layer consistently show the excess of iridium, the idea that the dinosaurs were exterminated by an asteroid remained a matter of controversy among geologists and paleontologists for more than a decade.
Officer and Gerta Keller have been critical of the theory.
Officer and Jake Page describe in their The Great Dinosaur Extinction Controversy  how A dust cloud from an asteroid impact could not have existed because many marine plants that require uninterrupted sunlight were unaffected The iridium deposits appear to be the work of volcanoes The extinctions occurred gradually, not instantaneously "Even if a meteoric impact occurred at K-T time, it simply could not explain the extinction record.
August Main articles: Chicxulub crater and Cretaceous—Paleogene extinction event Ina scientific drilling project drilled deep into the peak ring of the Chicxulub impact craterto obtain rock core samples from the impact itself.
The discoveries were widely seen as confirming current theories related to both the crater impact, and its effects.
They confirmed that the rock comprising the peak ring had been subjected to immense pressures and forces and had been melted by immense heat and shocked by immense pressure from its usual state into its present form in just minutes; the fact that the peak ring was made of granite was also significant, since granite is not a rock found in sea-floor deposits, it originates much deeper in the earth and had been ejected to the surface by the immense pressures of impact; that gypsuma sulfate -containing rock that is usually present in the shallow seabed of the region, had been almost entirely removed and must therefore have been almost entirely vaporized and entered the atmosphere, and that the event was immediately followed by a huge megatsunami a massive movement of sea waters sufficient to lay down the largest known layer of sand separated by grain size directly above the peak ring.
These strongly support the hypothesis that the impactor was large enough to create a mile peak ring, to melt, shock and eject basement granite from the midcrust deep within the earth, to create colossal water movements, and to eject an immense quantity of vaporized rock and sulfates into the atmosphere, where they would have persisted for a long time.
This global dispersal of dust and sulfates would have led to a sudden and catastrophic effect on the climate worldwide, large temperature drops, and devastated the food chain. Archived from the original on Many of the imaginative theories for the extinction of the dinosaurs will also be presented.
Within the uniformitarian paradigm, the meteorite impact theory, once considered ‘outrageous’, now is the dominant theory.
Asteroid Theory It was stipulated that a monolithic asteroid struck Earth that forced the similar of dinosaurs to extinction.
The theory was that the dust from the hit infuses in the upper ambiance which in return has caused planetary darkness. The Alvarez hypothesis posits that the mass extinction of the dinosaurs and many other living things during the Cretaceous–Paleogene extinction event was caused by the impact of a large Charles B.
Officer and Gerta Keller have been critical of the theory. Officer and Jake Page describe in their The Great Dinosaur Extinction Controversy. These apparently died out suddenly and simultaneously, and their extinction accords best with the asteroid theory.
The fossil evidence of land dwellers, however, suggests a gradual rather than a sudden decline in dinosaurian diversity (and possibly abundance). She views that the asteroid impact happened too early to cause the die-off and sees the findings in India as strength in the case that a volcanic eruption was the extinction event.
The great impact happened 66,, years ago -- within 30, years of the dinosaurs' extinction. When you're talking about things that happened tens of millions of years ago, that's pretty good.