首页
登录
职称英语
(1)Disaster struck 250 million years ago, when the worst devastation in the
(1)Disaster struck 250 million years ago, when the worst devastation in the
游客
2023-11-25
22
管理
问题
(1)Disaster struck 250 million years ago, when the worst devastation in the earth’s history occurred. Called the end-Permian mass extinction, it marks a fundamental change in the development of life.
(2)The history of life on the earth is replete with catastrophes of varying magnitudes. The one that has captured the most attention is the extinction of the dinosaurs and other organisms 65 million years ago—between the Cretaceous and Tertiary periods—which claimed up to half of all species. As severe as that devastation was, it pales in comparison to the greatest disaster of them all: the mass extinction some 250 million years ago, at the end of the Permian period. Affectionately called "the mother of mass extinctions" among paleontologists(with apologies to Saddam Hussein), it yielded a death toll that is truly staggering. About 90 percent of all species in the oceans disappeared during the last several million years of the Permian. On land, more than two thirds of reptile and amphibian families vanished. Insects, too, did not escape the carnage: 30 percent of insect orders ceased to exist, marking the only mass extinction insects have ever undergone.
(3)But from catastrophes, opportunities arise. For several hundred million years before the end-Permian event, the shallow seas had been dominated by life-forms that were primarily immobile. Most marine animals lay on the seafloor or were attached to it by stalks, filtering the water for food or waiting for prey. In the aftermath of the extinction, many once minor groups—active, predatory relatives of modern-day fish, squids, snails and crabs—were able to expand. Some completely new lineages appeared. This ecological reorganization was so dramatic that it forms a fundamental boundary in the history of life. Not only does it demarcate the Permian and Triassic periods, it also establishes the close of the Paleozoic era and the start of the Mesozoic era. The modern tidal pool reflects what lived and what died 250 million years ago.
(4)Over the past few years, exciting new insights into the causes and consequences of the end-Permian mass extinction have poured in from virtually every branch of the earth sciences. Some of these findings include detailed studies of rapid changes in ocean chemistry, more thorough documentation of extinction patterns and new analyses showing that large volcanic eruptions occurred at the Permo-Triassic boundary.
(5)How much do mass extinctions contribute to the evolution of a group, as compared with long-term adaptive trends? For example, sea urchins are ubiquitous in modern oceans but were relatively uncommon during the Permian. Only a single genus, Miocidaris, is known for certain to have survived the extinction. Did Miocidaris survive by pure chance, or was it better adapted? Would sea urchins today look any different had it not been for the end-Permian extinction?
(6)To resolve such questions, we need to learn more about the causes of the catastrophe and how those species that survived differed from those that disappeared. The key sources for this information are rock layers and fossils. Unfortunately, samples from the late Permian and early Triassic are notoriously difficult to come by. The fossil record across the boundary is plagued by poor preservation, a lack of rock to sample and other problems, including access. An extensive drop in sea level during the late Permian limited the number of marine rocks deposited on land, and many areas where the best rocks were preserved(most notably, in southern China)have been relatively hard for some geologists to reach.
(7)As such, it has proved difficult to ascertain just how quickly life was snuffed out or if the deaths were subject to any regional variations. Some creatures, especially those sensitive to changes in the environment, died off rapidly, as shown by Erik Flugel and his colleagues at the University of Erlangen, who arrived at this conclusion after examining reefs in southern China and Greece. Other evidence indicates more gradual loss of life.
(8)Intensive studies of newly found and critical boundary layers in Italy, Austria and southern China have helped our understanding. They indicate that the duration of the extinction is shorter than previously thought, implying that abruptly calamitous environmental conditions must have set in. [br] We can infer from the passage that_____.
选项
A、there is a general agreement over the causes of the end-Permian mass extinction
B、marine animals would have disappeared but for the end-Permian mass extinction
C、the insects can adapt themselves to the changeable environment in the history
D、the end-Permian mass extinction must have prevented the spread of the species
答案
A
解析
此题是道推论题。文章最后一段告诉我们新的关键证据得到了深入细致的研究,从而有助于我们对大灭绝原因的理解。选项A正是在此基础上作出的正确推断:对于二叠纪末大灭绝的原因已有总的一致意见。
转载请注明原文地址:https://tihaiku.com/zcyy/3218604.html
相关试题推荐
[originaltext]W:Twomillionhighschoolseniorsaregearingupthisfalltoap
[originaltext]W:Twomillionhighschoolseniorsaregearingupthisfalltoap
About25millionautoaccidentsoccurintheUnitedStateseachyear.Appro
About25millionautoaccidentsoccurintheUnitedStateseachyear.Appro
About25millionautoaccidentsoccurintheUnitedStateseachyear.Appro
About25millionautoaccidentsoccurintheUnitedStateseachyear.Appro
About25millionautoaccidentsoccurintheUnitedStateseachyear.Appro
It’stheholidayseasonandthatmeanskidsbythemillionsareaskingSant
It’stheholidayseasonandthatmeanskidsbythemillionsareaskingSant
It’stheholidayseasonandthatmeanskidsbythemillionsareaskingSant
随机试题
Theestrangedfriendsattempted(i)______buttheirdeep-seated(ii)______madeth
YouprobablythinkofHyundaiasthemakerofworld-class,highquality,aff
下列关于供水设施的维护管理规定,()对柴油机消防水泵的启动电池的电量进行检
以下哪些与阿片受体模型相符A.一个适合芳环的平坦区 B.有一个阳离子部位与药物
2012年,浙江省民办非企业单位的数量比2003年增加了:() A.588
振兴村2019年集体资产经营与财务收支业务如下: (1)1月,该村通过清产
物业服务采用包干制收费形式的,在市场不规范时,个别物业服务企业可能通过()来保证
在一定时间、空间和一定的条件下,运输消费者愿意购买且能够购买的运输服务的数量,称
(2018年真题)在采用借贷记账法进行时,资产类账户的记录规则是()。A.借方
机械使用过程的危险有害因素分为机械性有害因素和非机械性有害因素,下列选项中全部属
最新回复
(
0
)