This impact relead an enormous amount of energy, excavating a crater about twice as large as the lunar crater Tycho. The explosion lifted about 100 trillion tons of dust into the atmosphere. Such a quantity of material would have blocked the sunlight completely from reaching the surface, plunging Earth into a period of cold and darkness that lasted at least veral months. The explosion is also calculated to have produced vast quantities of nitric acid (硝酸) and melted rock that sprayed out over much of Earth, starting widespread fires that must have consumed most terrestrial forests and grassland. Presumably, tho environmental disasters could have been responsible for the mass extinction, including the death of the dinosaurs.
小学6年级数学辅导>艾薇儿结婚背景音乐trevalSeveral other mass extinctions in the geological record have been tentatively identified with large impacts, but none is so dramatic as the Cretaceous event. But even without such specific documentation, it is clear that impacts of this size do occur and that their results can be catastrophic. What is a catastrophe for one group of living things, however, may create opportunities for another group. Following each mass extinction, there is a sudden evolutionary burst as new species develop to fill the ecological niches opened by the event.
Impacts by meteorites reprent one way that could cau global catastrophes and riously influence the evolution of life all over the planet. According to some estimates, the majority of all extinctions of species may be due to such impacts. Such a perspective fundamentally changes our view of biological evolution. The standard criterion for the survival of a species is its success in competing with other species and adapting to slowly changing environments. Yet an equally important criterion is the ability of a species to survive random global ecological catastrophes due to impacts. 给某人打电话的英文
5. In paragraph 2, why does the author include the information that dinosaurs had flourished for tens of millions of years and then suddenly disappeared?
A. To support the claim that the mass extinction at the end of the Cretaceous is the best-documented of the dozen or so mass extinctions in the geological record.
B. To explain why as many as half of the species on Earth at the time are believed to have become extinct at the end of the Cretaceous.
C. To explain why paleontologists have always been intrigued by the mass extinction at the end of the Cretaceous]
D. To provide evidence that an impact can be large enough to disturb the environment of the entire planet and cau an ecological disaster.
6. According to paragraph 3, how did scientists determine that a large meteorite had impacted Earth?
championshipsA. They discovered a large crater in the Yucat region of Mexico.
感叹句句型B. They found a unique layer of diment worldwide.
usuC. They were alerted by archaeologists who had been excavating in the Yucat region.
dmvD. They located a meteorite with a mass of over a trillion tons.
7. According to paragraph 4, all of the following statements are true of the impact at the end of the Cretaceous period EXCEPT:
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