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
(1) As objects go, Earth is getting on in years. But it is definitely not ancient by cosmic standards. The very oldest native pl
(1) As objects go, Earth is getting on in years. But it is definitely not ancient by cosmic standards. The very oldest native pl
admin
2022-10-30
65
问题
(1) As objects go, Earth is getting on in years. But it is definitely not ancient by cosmic standards. The very oldest native planetary material we can examine are tiny zircon crystals that formed here about 4.4 billion years ago. But the universe has been around for approximately 13. 8 billion years, and has been building stars and forging heavy elements since it was some 200 million years old.
(2) That means that element-rich matter has been polluting interstellar space for a long, long while. Some of that matter, especially from older stars and supernova, has condensed and frozen into microscopic grains of silicate (硅酸盐) and carbon compounds. Eventually those Stardust grains might find themselves pulled into the gravity-well of new-forming stars, and planets. But the vigor and turmoil of star and planet formation can erase the evidence of the age of those building blocks.
(3) Some of the most ancient crumbs of building material we can study are those inside certain kinds of meteorites that still conveniently fall to Earth. Stardust swept up as the solar system combined.
(4) Now a study by Heck et al. , reported in the Proceedings of the National Academy of Sciences in the U.S. , seems to have located interstellar grains that are as old as 7. 5 billion years. Pre-dating our entire solar system by some 3 billion years.
(5) The investigation took material from the famous Murchison meteorite that fell and scattered across parts of Australia (including the town of Murchison) in 1969. This meteorite is a carbonaceous chondrite (碳质球粒陨石), a supremely "primitive" object, rich in carbon compounds. It represents material that attached together 4.5 billion years ago out of interstellar stuff—never being processed inside pro to-planetary interiors.
(6) By crushing a sample and dissolving it in acid, the researchers were able to isolate so-called pre-solar or interstellar grains—hardy little crumbs, barely several micrometers across.
(7) But how do you estimate their ages? It turns out that the universe provides, in a manner, a clock. Cosmic rays are constantly zipping through space, and when these energetic particles (like protons and alpha-particles) collide with the atomic nuclei in a grain the nuclear damage leaves an isotopic (同位素的) signature. The longer the grain has been floating around, the more of those nuclear changes accumulate.
(8) With a lot of additional detective work to account for different initial compositions from different stellar sources of elements, and all the potential traumas of heating and bashing around that the grains might have endured, it’s possible to use the cosmic ray signature to come up with an estimate of how long the grains were hanging around in interstellar space.
(9) In this case, using the accumulation of Neon-21 in particular, most of the grains in Murchison seem to be less than a few hundred million years old (commensurate with the amount of time they were originally adrift before getting stuck in the Murchison body). But at least 8% are astonishingly old, reaching back to approximately 7. 5 billion years, some two billion years older than any previous samples.
(10) The range of grain ages is also consistent with the idea that some 7.5 billion years ago there was a lot more star formation going on, not just in the Milky Way but across the universe.
(11) It’s a remarkable result, and one that demonstrates that sometimes the secrets of the cosmos can literally fall in our backyard. (本文选自 Scientific American)
Which of the following statements is TRUE about the study conducted by Heck et al. ?
选项
A、The age of the solar system has increased by 4.5 billion years.
B、The study wasn’t released in the academic journal.
C、They based their study on the material from a famous meteorite.
D、The sample they used was directly put and dissolved in acid.
答案
C
解析
细节题。第四至七段介绍了海克等人的研究。由第五段第一句可知,该研究从著名的默奇森陨石中获取了材料,故答案为C。由第四段最后一句可知,该研究找到了75亿年前的星际颗粒,比我们整个太阳系早30亿年,而不是45亿年,故排除 A;由第四段第一句可知,该研究发表在美国《国家科学院院刊》上,故排除B;由第六段第一句可知,研究人员先将样本敲碎,再将其溶解在酸里,并不是直接放在酸里溶解,故排除D。
转载请注明原文地址:https://kaotiyun.com/show/pVkK777K
0
专业英语四级
相关试题推荐
AllthefollowingsentencesdefinitelyindicatefuturetimeEXCEPT______
Noiseconstitutesarealandpresentdangertopeople’shealth.Dayandnight,athome,atwork,andatplay,noisecanproduce
WhichofthefollowingsentencesisINCORRECT?
Thisisalong_______—roughly20milesdownabeautifulvalleytothelittlevillagebelow.
WhichofthefollowingitalicizedphrasesisINCORRECT?
Whichofthefollowingprepositionalphrasesisusedasattributive?
WhatCausesJetLagandHowtoAvoidIt1.Facts■alongflightaffects【T1】________【T1】_________■thenatur
WhatCausesJetLagandHowtoAvoidIt1.Facts■alongflightaffects【T1】________【T1】_________■thenatur
Beingcolour-blind,Sallycan’tmakea_____betweenredandgreen.
A.famousB.conductedC.rejectD.influentialE.unrealisticF.developG.fail
随机试题
易患亚急性感染性心内膜炎的高危病变是
女性,45岁,偶然发现左乳房肿块,直径约2cm,质较硬、无压痛,与皮肤有少许粘连。左侧腋下可扪及1cm大小肿大的淋巴结。该病人的术后护理措施中不正确的是
设随机变量X的概率密度为则P(0≤X≤3)=()。
铸造作业过程中存在诸多的不安全因素,因此应从工艺、建筑、除尘等方面采取安全技术措施,工艺安全技术措施包括工艺布置、工艺设备、工艺方法、工艺操作。下列安全技术措施中,属于工艺方法的是()。
[背景资料]某高土石坝坝体施工项目,业主与施工总承包单位签订了施工总承包合同,并委托了工程监理单位实施监理。施工总承包完成桩基工程后,将深基坑支护工程的设计委托给了专业设计单位,并自行决定将基坑的支护和土方开挖工程分包给了一家专业分包单位施工。专业设计单
位于北京市的某生产企业,2014年企业会计核算的利润总额为200万元,其中销售收入是9282万元。经聘请的税务师审核,发现有关涉税问题如下:(1)企业拥有房产原值1000万元,其中1月1日将临街原值100万元的房屋出租两年,取得月租金是6万元,3
在诸多行政职能中,处在核心的地位和起主导作用的职能是行政决策。()
说中国是新殖民主义的人,总爱拿中、非之间的资源合作做文章,这是别有用心的______,完全没有道理。填入横线部分最恰当的一项是()。
在一次聚会上,10个吃了水果色拉的人中,有5个很快出现了明显的不适。吃剩的水果色拉立刻被送去检验。检验的结果不能肯定其中存在超标的有害细菌。因此,食用水果色拉不是造成食用者不适的原因。如果上述检验结果是可信的,那么以下哪项对上述论证的评价最为恰当?
数据库设计中,用E-R图来描述信息结构但不涉及信息在计算机中的表示,它属于数据库设计的()。
最新回复
(
0
)