托福考试 复习
TPO 33—3 灭绝事件
原文：posion
【1】It was not until the Cambrian period, beginning about 600 million years ago, that a great proliferation of macroscopic species occurred on Earth and produced a fossil record that allows us to track the ri and fall of biodiversity. Since the Cambrian period, biodiversity has generally rin, but th
ere have been some notable exceptions. Biodiversity collapd dramatically during at least five periods becau of mass extinctions around the globe. The five major mass extinctions receive most of the attention, but they are only one end of a spectrum of extinction events. Collectively, more species went extinct during smaller events that were less dramatic but more frequent. The best known of the five major extinction events, the one that saw the demi of the dinosaurs, is the Cretaceous-Tertiary extinction.
【2】Starting about 280 million years ago, reptiles were the dominant large animals in terrestrial environments. In popular language this was the era “when dinosaurs ruled Earth,”when a wide variety of reptile species occupying many ecological niches. However, no group or species can maintain its dominance indefinitely, and when, after over 200 million years, the age of dinosaurs came to a dramatic end about 65 million years ago, mammals began to flourish, evolving from relatively few types of small terrestrial animals into the myriad of diver species, including bats and whales, that we know today. Paleontologists la bel this point in Earth’s history as the end of the Cretaceous period and the beginning of the Tertiary period, often abbreviated as the K-T boundary. This time was also marked by changes in many马卢达是什么意思
other types of organisms. Overall, about 38 percent of the families of marine animals were lost, with
percentages much higher in some groups Ammonoid mollusks went from being very diver and abundant to being extinct. An extremely abundant t of planktonic marine animals called foraminifera largely disappeared, although they rebounded later. Among plants, the K-T boundary saw a sharp but brief ri in the abundance of primitive vascular plants such as ferns, club moss, hortails, and conifers and other gymnosperms. The number of flowering plants (angiosperms) was reduced at this time, but they then began to increa dramatically.
【3】What caud the changes? For many years scientists assumed that a cooling of the climate was responsible, with dinosaurs being particularly vulnerable becau, like modern reptiles, they were ectothermic (dependent on environmental heat, or cold-blooded). It is now widely believed that at least some species of dinosaurs had a metabolic rate high enough for them to be endotherms (animals that maintain a relatively consistent body temperature by generating heat internally). Nevertheless, climatic explanations for the K-T extinction are not really challenged by the ideas that dinosaurs may have been endothermic, becau even endotherms can be affected by a significant change in the climate.
【4】Explanations for the K-T extinction were revolutionized in 1980 when a group of physical scientists led by Luis Alvarez propod that 65 million years ago Earth was stuck by a 10-kilometer-
2016年12月六级
wide meteorite traveling at 90,000 kilometers per hour. They believed that this impact generated a thick cloud of dust that enveloped Earth, shutting out much of the incoming solar radiation and reducing plant
photosynthesis to very low levels. Short-term effects might have included huge tidal waves and extensive fires. In other words, a ries of events arising from a single cataclysmic event caud the massive extinctions. Initially, the meteorite theory was bad on a single line of evidence. At locations around the globe, geologists had found an unusually high concentration of iridium in the layer of dimentary rocks that was formed about 65 million years ago. Iridium is an element that is usually uncommon near Earth’s surface, but it is abundant in some meteorites. Therefore, Alvarez and his colleagues concludedthat it was likely that the iridium in dimentary rocks deposited at the K-T boundary had originated in a giant meteorite or asteroid. Most scientist came to accept the meteorite theory after evidence came to light that a circular formation, 180 kilometers in diameter in diameter and centered on the north coast of the Yucatan Peninsula, was created by a meteorite impact about 65 million years ago.
题目：
1.The word "proliferation" in the passage (paragraph 1) is clost in meaning to
A.decline.bluecoat
C.increa.快手刷赞业务网站平台
D.migration.
syntax error2.Paragraph 1 supports which of the following statements about life on Earth before the Cambrian period?
A.Biodiversity levels were steady, as indicated by the fossil record.
拉拉是啥意思
B.Levels of biodiversity could not be tracked.
C.The most dramatic extinction episode occurred.
D.Few microscopic species existed.
3.Which of the ntences below best express the esntial information in the highlighted ntence in the passage? Incorrect choices change the meaning in important ways or leave out esntial infor
mation.
A.The dominance of dinosaurs came to an end 65 million years ago, at which time mammals began to flourish and diversify.
少儿英语歌曲mp3
B.Becau no group of species can remain dominant forever, mammals became the dominant group when dinosaurs became extinct.
C.After being the dominant group for more than 200 million years, the age of dinosaurs came to a dramatic end 65 million years ago.
D.The diver group of mammals that we know today, including bats and whales, evolved from small terrestrial forms that had been dominated by dinosaurs.
4.According to paragraph 2, why are dinosaurs popularly said to have "ruled Earth" during the Cretaceous period?
A.Dinosaurs were the only species of reptile that existed during the whole of the Cretaceous period.
B.Dinosaurs won the battle for food resources over mammals during the Cretaceous period.
日语 加油C.Dinosaurs survived extinction during the Cretaceous period, whereas many other
>make sb
