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
91
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.
According to the passage, scientists haven’t had any doubt about a palaeontological doctrine that
选项
A、animal bodies tend to be destroyed by different elements.
B、some corpses of animals turn into preserved rock formation.
C、minerals from underground water form organic material.
D、the remains of animals are usually covered by sediment.
答案
B
解析
细节题。由题干中的palaeontological doctrine定位至第二段第一句“Such was palaeontologicaldoctrine for decades.”由“Such was”可知,应去上文,即第一段中查找具体描述。第一段提到,动物尸体在被快速掩埋之后,经过一个缓慢的过程,矿物质从地下水里沉淀进人封闭的动物体的有机质里,最终将有机质变成化石,[B]是对这一学说具体内容的概括表述,故为答案。
转载请注明原文地址:https://kaotiyun.com/show/nfdO777K
0
专业英语八级
相关试题推荐
Manyschool-leaversinwestcountriestakeagapyear,referringtoaperiodoftimeduringwhichhighschoolgraduatestakesa
Homeschoolingistoeducatechildrenathome,typicallybyparentsorsometimesbytutors,ratherthaninotherformalsettings
WhichofthefollowingisNOTcorrectaboutRaulandhiswork?
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
ModernExaminationsIntheschoolsofancienttimes,themostimportantexaminationswerespoken.Usuallythestudentsweres
Ofallthelessonstaughtbythefinancialcrisis,themostpersonalonehasbeenthatAmericansaren’ttooslickwithmoney.We
Mostofanimalscommunicatewithoneanothertoagreaterorlesserde-(1)______gree,andthemoresocialaspecies,themore
Whetheryoukeepallthereceiptsinashoeboxoruseonlinebanking,youshouldbeclearabout
FeelslikeSpringIstopatthecornerdrugstoreforabreakfastofdoughnutsandcoffee,andthenIracetothesubwaystati
Thereare______morphemesintheword"boyish".
随机试题
以下叙述中正确的是()。
输尿管芽经反复分支,逐渐演变为()
A.甲状腺危象B.喉上神经内支损伤C.喉上神经外支损伤D.喉返神经损伤甲状腺大部切除术后说话时音调降低提示
甲厂是一国有企业,因不能清偿到期债务,被几,家债权人诉至法院,某工商银行于1997年8月23日依法向人民法院提起诉讼,要求企业偿还长期拖欠的银行贷款,至1998年4月15日审结,判决甲厂偿还贷款及相应的利息,但还没有执行。某建设银行曾向甲厂提供一笔贷款一直
[2008年,第10题]设函数f(x)在[0,+∞)上连续,且f(x)=满足,则f(x)是()。
下列关于股份支付会计处理的表述中,不正确的是()。(2010年)
新课程改革用________代替了教学大纲。
收集数据时,设计调查的问题很重要。此时,需要注意的原则不包括(8)。
A.Adviceconcerningcreditcarduseabroadhasbeenformallycompiledinanewguide.Theguidanceincludestipsonwhatfeescr
In1950,ayoungmanwouldhavefounditmucheasierthanitistodaytogetandkeepajobintheautoindustry.Andinthatye
最新回复
(
0
)