An impact drove the dinosaurs extinct; or was it volcanoes?
Impact didn't lead to mass extinction 65 million years ago, geologists find
INTRODUCTION The K-T Extinction occurred 65 million years ago.
After Africa began colliding with Asia, about 18 mya Asian animals quickly invaded and dominated Africa. The two primary exceptions were , both of which prospered at home in Africa and in Eurasia. Proboscideans did even better; they did not only become prominent in Eurasia, but they also migrated to North America by 16.5 mya. , as soon as they could, and quickly succeeded in all South American biomes, from rainforest to grasslands to mountains. They beat apes to the Western Hemisphere by 16.5 million years. Elephants have and . Their huge size and prehensile trunks, as well as their ability to eat a wide variety of vegetation, let proboscideans flourish everywhere that they possibly could. They even as a force. Until humans arrived, proboscideans were the most intelligent, adaptable, and successful land mammals ever and arguably outperformed the dinosaurs. But after nearly 20 million years of global success, they nearly all went extinct soon after encountering behaviorally modern humans. They went extinct in the Western Hemisphere, and there has long been controversy among scientists whether humans caused it, although the debate is fading as evidence of human agency becomes clearer.
For example, even in the 1980s a new book on dinosaur extinctions suggested that they spent too much time in the sun, got cataracts, and because they couldn't see very well, fell over cliffs to their doom.
We know for sure most dinosaurs died out around 65 million years ago.
The thing is the atmosphere isvery thin in that region, and so, the asteroid would have been much more likely to penetrate without breaking up than theone 65 million years ago.
When one electron shell is filled, electrons begin to fill shells farther from the nucleus. For the simplest atoms it works that way, but for larger atoms, particularly those of metallic elements, electrons fill shells in more complex fashion and electrons begin to fill subshells not necessarily in the shell closest to the nucleus. When an electron is unpaired or in an unfilled shell, it can be a electron, which can form bonds with other atoms. In most circumstances, only unpaired electrons form bonds with other atoms. Electron bonds between atoms provide the basis for chemistry and life on Earth.
Evolution: Extinction: What Killed the Dinosaurs? - PBS
Compared to the recovery from the mass extinctions that ended the , , and periods, the recovery from the end-Cretaceous extinction was relatively swift. The seafloor ecosystem was fully reestablished within two million years. But the story on land was spectacularly different. By the Paleocene’s end, ten million years after the end-Cretaceous event, all mammalian orders had appeared in what I will call the “Mammalian Explosion.” While the fossil record for Paleocene mammals is relatively thin, the Mammalian Explosion is one of the most spectacular evolutionary radiations on record. Because of its younger age, the Cenozoic Era’s is generally more complete than those of previous eras.
So far in this essay, mammals have received scant attention, but the mammals’ development before the Cenozoic is important for understanding their rise to dominance. The , called , first , about 260 mya, and they had key mammalian characteristics. Their jaws and teeth were markedly different from those of other reptiles; their teeth were specialized for more thorough chewing, which extracts more energy from food, and that was likely a key aspect of success more than 100 million years later. Cynodonts also developed a secondary palate so that they could chew and breathe at the same time, which was more energy efficient. Cynodonts eventually ceased the reptilian practice of continually growing and shedding teeth, and their specialized and precisely fitted teeth rarely changed. Mammals replace their teeth a . Along with tooth changes, jawbones changed roles. Fewer and stronger bones anchored the jaw, which allowed for stronger jaw musculature and led to the mammalian (clench your teeth and you can feel your masseter muscle). Bones previously anchoring the jaw were no longer needed and . The jaw’s rearrangement led to the most auspicious proto-mammalian development: . Mammals had relatively large brains from the very beginning and it was probably initially . Mammals are the only animals with a , which eventually led to human intelligence. As dinosaurian dominance drove mammals to the margins, where they lived underground and emerged to feed at night, mammals needed improved senses to survive, and auditory and olfactory senses heightened, as did the mammalian sense of touch. Increased processing of stimuli required a larger brain, and . In humans, only livers use more energy than brains. Cynodonts also had , which suggest that they were warm-blooded. Soon after the Permian extinction, a cynodont appeared that may have ; it was another respiratory innovation that served it well in those low-oxygen times, functioning like pump gills in aquatic environments.
Dinosaur-killing asteroid impact may have cooled …
Meteorites, Impacts, & Mass Extinction - Tulane …
Sediments show that the Chicxulub meteorite predates a mass extinction 65 million years ago.
Meteorites, Impacts, and Mass Extinction
McKay Planetarium in Melbourne, Australia discusses the impact theory for the extinction of the dinosaurs.
Cause of dinosaur extinction; ..
They suggest all extinction is caused by environmental stresses, such as the impact that killed the dinosaurs.
Dinosaur Extinctions: No Asteroid or Comet Impact Here
The impact theory or the possibility that an asteroid or cometdestroyed over half of the species on earth has been a stronglysupported theory of why the dinosaurs became extinct. The impact of theasteroid or comet caused a chain of events beginning with the flyingobject becoming intensely hot and heading towards earth . This asteroid is believed to impact the ocean "ejecting massive amounts of dust and water into the atmosphere" . Everything within the radius of 500 kilometers would have been instantly destroyed .Many of the groups of organisms that were hit hardest by the K/T extinction lived in the ocean .Manyenormous tidal waves would be started causing even more damage as wellas start a chain reaction of earthquakes and volcanic activity .Thedust particles will envelop the earth covering the earth into totaldarkness making vegetation to dematerialize away, leave little food forthe animals, and create a cold environment .Temperatures may have fluctuated below freezing point to high temperatures and photosynthesis may have ceased .Atthe same time large fires would have been started by the intense shockwave later creating global fires that would release large amounts ofcarbon dioxide increasing temperatures and cause chemical reactionsforming acid rain .Theimpact may also have released sulfur dioxide, which may help createdacid rain with a low pH causing an environment where some organism maynot have been able to survive .Evidence of acid rain was found in a number of rock samples (1).
Dinosaur Extinctions: No Asteroid or Comet ..
One of the greatest discoveries that show great support for the impact theory is a crater called the Chicxulub,, ,.Alan Hildebrand found a ring structure 180 kilometers in diameter inthe Yucatan Peninsula. The Chicxulub is also believed to be 65 millionyears old. Alan Hildebrand wrote further explaining that the K/Tboundary had two layers .Theupper layer, the Fireball layer, was about 3mm thick and represented1500 cubic kilometers of debris deposited globally with not variationin thickness. The Lower layer, the ejecta layer, was about 2mm thick .The Fireball layer contains certain traces of elements in approximately the same proportion as some meteorites .Furthermore,Tektites and micro tektites, black glassy objects produced at the timeof the impact, have been found in the ejecta layer of the K-T boundary .
An illustration of dinosaurs fleeing a meteorite impact
The volcanic theory is somewhat similar to the impact theory and isalso heavily supported by a number of scientists. As mentioned beforethe K/T boundary was discovered to have high contents of iridium. Thebasaltic lava eruptions of the Deccan Traps of western India wasmentioned as a possible source of the iridium found in the K/T boundary"iridium spike" ."It has been proposed that the out gassing, combined with possibleexplosive episodes, could have been sufficient of itself to have causedthe same kind of a "Nuclear Winter" scenario as proposed for the giantmeteor impact" . Other areas in the Pacific Basin show a fairly high level of volcanic eruptions .This theory would further explain the possibility of how some organismssurvived and the irregular distribution of iridium peaks in some areas.
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