Explaining Dinosaur Extinction
Dinosaurs rapidly became extinct about 65 million years ago as part of a mass extinction known as the K–T event, becau it is associated with a geological signature known as the K–T boundary, usually a thin band of dimentation found in various parts of the world (K is the traditional abbreviation for the Cretaceous, derived from the German name Kreidezeit). []Many explanations have been propod for why dinosaurs became extinct.[] For example, some have blamed dinosaur extinction on the development of flowering plants, which were suppodly more difficult to digest and could have caud constipation or indigestion-except that flowering plants first evolved in the Early Cretaceous, about 60 million years before the dinosaurs died out.[] In fact, veral scientists have suggested that the duckbill dinosaurs and horned dinosaurs, with their complex battery of grinding teeth, evolved to exploit this new resource of rapidly growing flowering plants.[] Others have blamed extinction on competition from the mammals, which 清空缓存allegedly ate all the dinosaur eggs-except that mammals and dinosaurs appeared at the same time in the Late Triassic, about 190 million years ago, and there is no reason to believe that mammals suddenly acquired a
taste for dinosaur eggs after 120 million years of coexistence. Some explanations (such as the one stating that dinosaurs all died of dias) fail becau there is no way to scientifically test them, and they cannot move beyond the realm of speculation and guesswork.
In paragraph 1, why does the author include a discussion of when flowering plants evolved?
∙ To help explain why some scientists believe that the development of flowering plants led to dinosaur extinction
偏头痛吃什么∙ To cast doubt on the theory that the development of flowering plants caud dinosaurs to become extinct
∙ To suggest that dinosaurs were able to survive for as long as they did becau of the availability of flowering plants
∙ To emphasize that duckbill dinosaurs and horned dinosaurs were the first dinosaurs to b
ecome extinct
The word "allegedly" in the passage is clost in meaning to反思英语
∙ inevitably
∙ gradually
∙ suppodly
∙ increasingly
According to paragraph 1, the extinction of the dinosaurs is unlikely to have been the result of competition from mammals becau
∙ mammals would not have been capable of eating dinosaur eggs 萝卜干咸菜
∙ mammals did not appear in any significant numbers until after the Late Triassic
∙ mammals and dinosaurs did not, in fact, compete for any of the same resources
∙ mammals and dinosaurs lived together for roughly 120 million years before the extinction
This focus on explaining dinosaur extinction miss an important point: the extinction at the end of the Cretaceous was a global event that killed off organisms up and down the food chain. It wiped out many kinds of plankton in the ocean and many marine organisms that lived on the plankton at the ba of the food chain. The included a variety of clams and snails, and especially the ammonites, a group of shelled squidlike creatures that dominated the Mesozoic as and had survived many previous mass extinctions. The K–T event marked the end of the marine reptiles, such as the mosasaurs and the plesiosaurs, which were the largest creatures that had ever lived in the as and which ruled the as long before whales evolved. On land, there was also a crisis among the land plants, in addition to the disappearance of dinosaurs. So any event that can explain the destruction of the ba of the food chain (plankton in the ocean, plants on land) can better explain what happened to organisms at the top of the food chain, such as the dinos
aurs. By contrast, any explanation that focus strictly on the dinosaurs completely miss the point. The Cretaceous extinctions were a global phenomenon, and dinosaurs were just a part of a bigger picture.
According to paragraph 2, what is problematic about some scientists' focus on dinosaur extinction?
∙ Dinosaurs became extinct so long ago that no theory about their disappearance can be proven scientifically.
∙ Dinosaurs were not the only organisms that went extinct at the end of the Cretaceous period.
∙ More marine organisms went extinct during the Cretaceous than did dinosaur species.
∙ It is more important to understand how plankton and other marine organisms came to thrive during the Cretaceous period.
为什么不能生育
According to paragraph 2, each of the following became extinct during the K–T event EXCEPT
∙ early species of whales
∙ 决然是什么意思marine reptiles
∙ various species of clams 学问的近义词
∙ many species of land plants
What makes the extinction of "the ammonites" especially significant?
∙ They were among the largest creatures that ever lived.
∙ They existed at the lowest level of the food chain.
∙ They had been able to survive in the Mesozoic as.
∙ They had survived many previous mass extinctions.
According to one theory, the Age of Dinosaurs ended suddenly 65 million years ago when a giant rock from space plummeted to Earth. Estimated to be ten to fifteen kilometers in diameter, this bolide (either a comet or an asteroid) was traveling at cosmic speeds of 20–70 kilometers per cond, or 45,000–156,000 miles per hour. Such a huge mass traveling at such tremendous speeds carries an enormous amount of energy. When the bolide struck, this energy was relead and generated a huge shock wave that leveled everything for thousands of kilometers around the impact and caud most of the landscape to burst into flames. The bolide struck an area of the Yucatán Peninsula of Mexico known as Chicxulub, excavating a crater 15–20 kilometers deep and at least 170 kilometers in diameter. The impact displaced huge volumes of awater, causing much flood damage in the Caribbean. Meanwhile, the bolide itlf excavated 100 cubic kilometers of rock and debris from the site, which ro to an altitude of 100 kilometers. Most of it fell back immediately, but some of it remained as dust in the atmosphere for months. This material, along with the smoke from the fires, shrouded Earth, creating a for
补充条款m of nuclear winter. According to computerized climate models, global temperatures fell to near the freezing point, photosynthesis halted, and most plants on land and in the a died. With the bottom of the food chain destroyed, dinosaurs could not survive.
