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
When most animals die, nature likes to tidy up by making their bodies disappear. The remains get eaten by scavengers, bones are
When most animals die, nature likes to tidy up by making their bodies disappear. The remains get eaten by scavengers, bones are
admin
2015-01-09
84
问题
When most animals die, nature likes to tidy up by making their bodies disappear. The remains get eaten by scavengers, bones are scattered, tissues rot away and anything left over tends to get destroyed by the elements. Very occasionally, though, these destructive processes get disrupted. This usually happens when the corpse is quickly buried by sediment deposited by a river or blown in by the wind. Then begins a slow process in which minerals precipitate from groundwater into the encased organic material, eventually replacing it with a stony replica: a fossil.
Such was palaeontological doctrine for decades. But in recent years traces of soft tissue, such as blood vessels and bone cells, have been found in some dinosaur fossils. Now researchers have come up with an explanation for how these tissues were preserved for millions of years, which just might make it possible to extract some elements of prehistoric DNA.
That there was more in a fossil than meets the eye emerged in 2005 when Mary Schweitzer, a palaeobiologist at North Carolina State University, found something unusual after her team used acid to dissolve minerals from a fossilised piece of Tyrannosaurus rex bone. Left behind were some fibrous tissue, transparent blood vessels and cells. Many argued that this material must have come from modern bacteria and not a T. rex, since nothing organic could possibly survive the 68m years since the creature had walked the Earth.
In 2012, however, Dr. Schweitzer and her colleagues revealed the presence of proteins in a dinosaur fossil freshly dug up and carefully protected from any potential contamination. Moreover, one of the proteins the researchers identified could be found only in birds. Since dinosaurs were the ancestors of modern birds, the discovery made it hard to argue that soft-tissue material in the fossil could have come from bacterial contamination. Still, many scientists wondered how such a thing was possible.
In Proceedings of the Royal Society, Dr. Schweitzer and her colleagues collaborated with a team led by Mark Goodwin, a palaeontologist at the University of California, to seek an explanation. Organic material from dinosaur bones was studied using micro x-ray absorption spectroscopy, which allows scientists to examine the structure of matter using intense light beams. This led Dr. Goodwin to notice something remarkable: the organic material in the samples was thickly laced with iron nanoparticles. In animals, iron is most commonly found in blood and this led the researchers to wonder if the iron had come from blood cells that had once flowed through their dinosaur’s veins. Could it have played a part in the preservation of the tissues?
To test this idea, the researchers designed an experiment using freshly slaughtered ostriches which, being large and flightless birds, seemed to be a reasonable modern equivalent to dinosaurs. They extracted blood vessels from the bones of the birds and soaked them in a haemoglobin solution obtained from ruptured ostrich blood cells for 24 hours. The samples were then placed in both a saline solution and sterile distilled water. As a control, some of the blood vessels were put straight into saline solution or water without being pre-soaked in blood.
As expected, the ostrich tissues that went directly into the water and the saline solution fell apart rapidly and were entirely consumed by bacteria or heavily degraded in just three days. The same thing happened to the tissue soaked in haemoglobin and placed in water. But the treated sample in the saline solution remained intact and has stayed that way for two years now, with no signs of bacterial growth.
Dr. Schweitzer and Dr. Goodwin believe that highly reactive ions known as free radicals, which are produced by iron as it is released from the haemoglobin, interact with the organic tissue causing abnormal chemical bonds to form. These bonds effectively tie proteins in knots at the molecular level, much as the preservative formaldehyde does. This knot-tying makes the proteins unrecognizable to the sorts of bacteria that would normally consume them. This, they theorise, is how the soft tissues manage to survive for millions of years without rotting away.
The iron nanoparticles, however, may be doing more than just preserving tissues. Despite what happens in the science fiction world of "Jurassic Park", no dinosaur DNA has yet been found. The reason for this is that DNA is thought to have a half-life of 521 years, which means that, after that much time, half of the bonds between the proteins that make up DNA have broken apart; after another 521 years, another half have gone, and so on. This leaves very little behind after hundreds of thousands of years yet alone the 65m years or so that stand between humanity and dinosaurs. Even so, Dr. Schweitzer and Dr. Goodwin still wondered if the iron-based preservation process might allow DNA to bypass its typical half-life and last a lot longer.
To find that out, the team used an iron-removal compound known as pyridoxal isonicotinic hydrazide and added four different stains that react only with either DNA itself, or with proteins closely associated with it in organisms other than microbes. Remarkably, in all cases, these specific stains lit up inside the ancient cells in the tissue samples. This hints that something chemically very similar to DNA can remain in a fossil and might yet be hidden precisely where it had resided during life.
The author’s attitude toward Dr. Schweitzer and Dr. Goodwin’s speculation on the possibility of DNA preservation is
选项
A、skeptical.
B、supportive.
C、indifferent.
D、optimistic.
答案
B
解析
态度题。作者详细介绍了史怀哲博士和古德温博士的实验与发现,并在最后一段评价这项实验暗示了化石中可能存在着与DNA所含元素相近的化学物质,这说明作者对两位研究者的观点是认同与支持的,故答案为[B]。
转载请注明原文地址:https://kaotiyun.com/show/bfdO777K
0
专业英语八级
相关试题推荐
FiveCommonMistakesinConversationsandTheirSolutionsI.NotlisteningA.Problem:mostpeopledon’tlisten—waiteagerlyf
Underthe1996constitution,all11ofSouthAfrica’sofficiallanguages"mustenjoyequalityofesteemandbetreatedequitably
CharacteristicsofAmericanCultureI.PunctualityA.Goingtothetheaterbe(1)_____twentyminutesprior(1)______B.Eate
GuoXue,orthestudiesofChineseancientcivilization,includingphilosophy,history,archaeology,literature,linguistics,et
什么叫做“古典的”?“古典”一字在古代是指第一流的诗人,从字源上说是从“等级”这个词演化出来的。古人说“古典的”,等于今人说“头等的”;在近代则是指可以作为典范的作家或作品,因此古代希腊拉丁的文学被称为“古典的”。我们所说的“古典的”实际上包括“古代的”与
TheDeadSea,thelowestpointonearthandthelargest"NaturalSpa"intheworld,isalsooneoftheworld’struenaturalwond
Ineducation,Nigeriahasamothertonguepolicywhichrequiresthateverychildistaughtinamothertongueatthepreprimary【
Ineducation,Nigeriahasamothertonguepolicywhichrequiresthateverychildistaughtinamothertongueatthepreprimary【
WhichofthefollowingitemdoesNOTbelongtotheallomorphsofthemorpheme{-ed}?
长期以来,科学与艺术之间的关系一直是剃头担子一头热:科学热恋着艺术,艺术却拒科学于千里之外。许多大科学家一生钟爱艺术,且懂艺术,从中汲取养料,善养浩然之气,或得到人生最大安慰。相反,热爱自然科学并且理解工程技术的文学艺术家真可谓凤毛麟角。
随机试题
关于肾损伤患者进行非手术治疗的护理措施叙述不正确的是()。
维持子宫在正常位置,是由( )
某公司2000年6月以出让方式取得一宗位于某市某区某路×号的国有土地使用权,面积为18600m2,用途为工业,已办理土地登记手续。2004年5月,该公司拟以其所使用的国有出让土地作抵押,向某银行申请贷款。为验证该公司土地状况的真实性,降低银行贷款风险,现该
下列选项属于标准输入输出设备接口的是()。
甲公司适用所得税税率为15%,其2016年发生的交易或事项中,会计与税收处理存在差异的事项如下:①当期购入作为可供出售金融资产的股票投资,期末公允价值大于取得成本160万元;②收到与资产相关政府补助1600万元,不属于免税收入,相关资产至年末尚未开始计提折
From:ChadBecker,theDirectorofPersonnelTo:EmployeesOurfinancialadvisorshavefinallyreacheda【K4】______onaplan
新入职教师因不熟悉学校教学工作的相关规章制度,导致了较高的教学事故率。以S中学为例,尽管新入职教师占该校教师总数不足5%,但是在因教学事故给予处分的教师中,新入职教师占了25%。以下各项如果为真,除哪项外均能削弱上述结论?
某二叉树有5个度为2的结点,则该二叉树中的叶子结点数是()。
"You"inthepassagewanttogototheschool."You"willfirstmmleft,andthenmmright.
Whatpoliticianscherishmostisthebenefitsoftheirparties.Theunderlinedpartmeans________.
最新回复
(
0
)