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
Rubidium, potassium and carbon are three common elements used to date the history of Earth. The rates of radioactive decay of th
Rubidium, potassium and carbon are three common elements used to date the history of Earth. The rates of radioactive decay of th
admin
2015-04-24
71
问题
Rubidium, potassium and carbon are three common elements used to date the history of Earth. The rates of radioactive decay of these elements are absolutely regular when averaged out over a period of time; nothing is known to change them. To be useful as clocks, the elements have to be fairly common in natural minerals, unstable but decay slowly over millions of years to form recognizable "daughter" products which are preserved minerals.
For example, an atom of radioactive rubidium decays to form an atom of strontium(another element)by converting a neutron in its nucleus to a proton and releasing an electron, generating energy in the process. The radiogenic daughter products of the decay — in this case strontium atoms — diffuse away and are lost above a very high temperature. So by measuring the exact proportions of rubidium and strontium atoms that are present in a mineral, researchers can work out how long it has been since the mineral cooled below that critical "blocking" temperature. The main problems with this dating method are the difficulty in finding minerals containing rubidium, the accuracy with which the proportions of rubidium and strontium are measured, and the fact that the method gives only the date when the mineral last cooled below the blocking temperature. Because the blocking temperature is very high, the method is used, mainly for recrystallized(igneous or metamorphic)rocks, not for sediments — rubidium-bearing minerals in sediments simply record the age of cooling of the rocks which were eroded to form the sediments, not the age of deposition of the sediments themselves.
Potassium decays to form(a gas)which is sometimes lost from its host mineral by escaping through pores. Although potassium-argon dating is therefore rather unreliable, it can sometimes be useful in dating, sedimentary rocks because potassium is common in some minerals which form in sediments at low temperatures. Assuming no argon has escaped, the potassium-argon date records the age of the sediments themselves.
Carbon dating is mainly used in archaeology. Most carbon atoms(carbon-12)are stable and do not change over time. However,
cosmic
radiation bombarding the upper atmospheres constantly interacting with nitrogen in the atmosphere to create an unstable form of carbon, carbon-14.
The underlined word "cosmic" in the last paragraph is closest in meaning to______.
选项
A、radioactive
B、organic
C、terrestrial
D、universal
答案
D
解析
语义题。根据题干信息定位到原文尾段尾句。cosmic意为“宇宙的”。选项中,radioactive“放射性的,有辐射功能的”;organic“器官的,有机的,有组织的”;terrestrial“陆地”。universal“普遍的;通用的;宇宙的”。故答案为D。
转载请注明原文地址:https://kaotiyun.com/show/vgLO777K
0
考博英语
相关试题推荐
Thereisanewtypeofsmalladvertisementbecomingincreasinglycommoninnewspaperclassifiedcolumns.Itissometimesplaced
Theriseof"temp"workhasfurthermagnifiedthedecreasingrightsandalienationoftheworker.ItiscommoncorporatePractic
Theriseof"temp"workhasfurthermagnifiedthedecreasingrightsandalienationoftheworker.ItiscommoncorporatePractic
Researchiscommonlydividedinto"applied"and"pure".Thisclassificationisarbitraryandloose,butwhatisusuallymeantis
Researchiscommonlydividedinto"applied"and"pure".Thisclassificationisarbitraryandloose,butwhatisusuallymeantis
GeniusThegreatestresultsinlifeareattainedbysimplemeans,andtheexerciseofordinaryqualities.Thecommonlifeof
GeniusThegreatestresultsinlifeareattainedbysimplemeans,andtheexerciseofordinaryqualities.Thecommonlifeof
TheAmericaneconomy,whetheringovernmentorprivateindustry,hasfoundretirementaconvenientpracticeformanagingthelab
Theageatwhichyoungchildrenbegintomakemoraldiscriminationsaboutharmfulactionscommittedagainstthemselvesorothers
随机试题
生产强度指的是某一台设备单位特征几何量的()。
毛泽东比较全面总结农业合作化运动基本经验的报告是()
流行病学研究设计关注的一个中心问题是_______。
下述工作中,属于施工过程质量控制的是()
在下列指标中,属于杜邦分析体系起点的指标是()。
挂一个漂亮的鸟笼在房间里最显眼的地方,过不了几天,主人一定会做出下面两个选择之一:把鸟笼扔掉,或者买一只鸟回来放在鸟笼里。这就是鸟笼逻辑。这对于我们的启示是()。
下列名词与内容对应不一政的是:
2005年4月24日~27日,十届全国人大常委会第十五次会议在北京举行,审议通过的草案有
设A为二阶矩阵,α1,α2为线性无关的二维列向量,Aα1=0,Aα2=2α1+α2,则A的非零特征值为______。
Completetheformbelow.WriteNOMORETHANTHREEWORDSAND/ORANUMBERforeachanswer.Reportonabandoned
最新回复
(
0
)