首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
It has long been recognized that the dinosaurs disappeared from the fossil record at the end of the Cretaceous period (65 millio
It has long been recognized that the dinosaurs disappeared from the fossil record at the end of the Cretaceous period (65 millio
admin
2022-07-08
38
问题
It has long been
recognized
that the dinosaurs disappeared from the fossil record at the end of the Cretaceous period (65 million years ago), and as more knowledge has been gained, we have learned that many other organisms disappeared at about the same time. The microscopic plankton (free-floating plants and animals) with calcareous shells suffered massively. The foundation of the major marine food chain that led from the minute plankton to shelled animals to large marine reptiles had collapsed.
On land it was not only the large animals that became extinct. The mammals, most of which were small, lost some 35 percent of their species worldwide. Plants were also affected. For example, in North America 79 percent did not survive, and it has been noted that the survivors were often deciduous—they could lose their leaves and shut down—while others could survive as seeds. As in the sea, it seems that on the land one key food chain collapsed: the one with leaves as its basic raw material. These leaves were the food of some of the mammals and of the herbivorous dinosaurs, which in turn were fed on by the carnivorous dinosaurs. Furthermore, it is most likely that these large dinosaurs had slow rates of reproduction, which always increases the risk of extinction. Crocodiles, tortoises, birds, and insects seem to have been little affected. The two first named are known to be able to survive for long periods without food, and both can be scavengers. Indeed, with the deaths of so many other animals and with much dead plant material, the food chain based on detritus would have been well-supplied. Many insects feed on dead material; furthermore, most have at least one resting stage in which they are very resistant to damage. In unfavorable conditions some may take a long time to develop: there is a record of a beetle larva living in dead wood for over 40 years before becoming an adult. Some birds were scavengers, but the survival of many lineages is a puzzle.
What happened in the biological story just after these extinctions? What is found in and just above the boundary layer between the deposits of the Cretaceous and those of the Tertiary termed the K/T boundary. For a very short period the dominant microorganisms in marine deposits were usually diatoms and dinoflagellates (both single-celled types of plankton). The important feature for the survival of both these groups was the ability to form protective cysts (sacs around organisms) that rested on the sea floor. Above these, in the later deposits, are the remains of other minute plankton, but the types are quite different from those of the Late Cretaceous. In terrestrial deposits a sudden and dramatic increase in fern plant spores marks the boundary in many parts of the world; ferns are early colonizers of barren landscapes. The fern spike (sudden increase), as it is termed, has been found also in some marine deposits (such was the abundance of fern spores blown around the world), and it occurs in exactly the same layer of deposit where the plankton disappear. We can conclude that the major marine and terrestrial events occurred
simultaneously
.
Many theories have been put forward for the extinction of the dinosaurs, but most of them can be
dismissed
. In 1980, Louis Alvarez and Walter Alvarez and colleagues from the University of California published their research on the amounts of various metals in the boundary between Cretaceous and Tertiary rocks (K/T boundary) in Italy, Denmark, and New Zealand. They had found, accidentally, that a rare metal, iridium, suddenly became very abundant exactly at the boundary and then slowly fell away. This phenomenon, known as the iridium spike, has now been identified in K/T boundary deposits in over a hundred other sites in the world. Iridium occurs in meteorites and volcanic material, but in the latter case it is accompanied by
elevated
levels of nickel and chromium. These other metals are not especially abundant at the K/T boundary. The Alvarezes concluded that the iridium spike was due to a large asteroid that struck Earth 65 million years ago.
According to the second paragraph, which of the following factors probably contributed to the extinction of the dinosaurs?
选项
A、The length of time it took dinosaurs to reproduce.
B、Large quantities of dead material disturbing their habitats.
C、Increased competition for food from scavengers.
D、An increase in carnivore populations.
答案
A
解析
第2段第7句提到这些大型恐龙繁殖速度很慢(had slow rates of reproduction),因而会增加灭绝的风险(increases the risk of extinction),这说明A项“恐龙繁殖所需的时间”是可能导致恐龙灭绝的一个因素,故选A项。B项、C项和D项均是利用文中个别字词拼凑而成,不符合题意。
转载请注明原文地址:https://kaotiyun.com/show/SpMO777K
本试题收录于:
CATTI二级笔译综合能力题库翻译专业资格(CATTI)分类
0
CATTI二级笔译综合能力
翻译专业资格(CATTI)
相关试题推荐
RichDiseasesinPoorCountriesNon-communicablediseasesusedtobearich-worldproblem.Atthattime,peopleinpoorcount
Whenone’sknowledgeandabilitiescannotmatchhisworkdemands,thestressmayhappen.
PatrickMarkeyfoundthatmenwhocommitsevereactsofviolenceactuallyplayviolentvideogameslessthantheaveragemale.
Spurredbyawarmingclimate,daily【C1】______hightemperaturesoccurredtwiceasoftenasrecordlowsoverthelastdecadeacros
Therewasatimewhentheconceptofcreativitywasonlyassociatedwithwriters,painters,musiciansandsimilarpeopleinarti
OneofthemostbasicmoralvaluesforAmericansis【C1】_______.Thewell-known【C2】______aboutGeorgeWashingtonandthecherryt
Onlyhotelguestshavethe______ofusingtheprivatebeach.
Comparedwiththeimmediatepracticalresponsibilityofthescientist,the(1)oftheartistmustseempuny.Thedecisionwhich
Hewasfinallyenrolledintoamemberofthecollegeafterayear’shardworking.
Theactresswasvery______attheinsultingquestionraisedbyheropponentattheconference.
随机试题
电渣焊的电极材料有什么要求?
患者,男,50岁。幼年患麻疹后反复咳嗽,迁延不愈,常咳脓痰。近半月加重,咳大量脓性臭痰,每日量约120~150ml。伴高热、气促。目前确诊本病的首选检查方法是
观察内听道及迷路时,汤氏位摄影,中心线应
背景某机场施工单位在场道土石方施工中,发生了以下情况:(1)选用了4m3的挖掘机,载重12t的自卸汽车;(2)石方爆破的承包单位用敷炮的方式处理大块;(3)在填方施工时,对填方土的含水量没有严格控制。含水量对土的压实度是否有影响?
下列变量中,属于顺序变量的是()。
在股份有限公司中,签署公司股票是()的职权。
人在发展过程中,短时记忆的广度的峰值在()。
结合实际谈谈德育过程中知、情、意、行的互动影响。
特别行政区的行政机关是()。
一项研究把一群有慢性抑郁症的人与另一群在其他方面一致、但没有抑郁症的人进行了对比,发现抑郁症群体中明显有更多的免疫系统失调。根据研究人员的说法,这些结果强有力地支持了精神状况会影响身体对传染病的抵抗能力的观点。以下哪项如果为真,向研究人员的发现解释提出了最
最新回复
(
0
)