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
What is the main purpose of the lecture? According to the professor, what is the chemical index of alteration used for?
What is the main purpose of the lecture? According to the professor, what is the chemical index of alteration used for?
admin
2022-07-28
20
问题
What is the main purpose of the lecture?
According to the professor, what is the chemical index of alteration used for?
Listen to part of a lecture in a geology class.
Professor:
So continuing with ice ages, we’ve looked at the Pleistocene Ice age up through the so-called Little Ice age in Europe, but today I’d like to talk about a controversial hypothesis that Earth went through tremendous ice ages before all these others between approximately 600 and 700 million years ago during a geologic period that’s known as the Cryogenian.
Cryo is from the Greek and means cold. The name comes from the glacial deposits going back to this period. They’re found all around the world, which indicates that glaciers spread across all the continents at that time even near the equator.
And this is the premise of a hypothesis commonly called Snowball Earth. The name pretty much described the condition, that it is just proposed existed with not only the continents, but also the oceans entirely covered with thick sheets of ice.
But how could the Snowball Earth climate have come about? In the other ice ages, we’ve looked at, up to 30% of the Earth’s surface was covered in ice. But here we’re talking way more than that.
Okay. This gives us a chance for review. When radiation from the sun reaches our planet, some of it is absorbed and some of it reflected back into space, right? And different surfaces on Earth reflect solar radiation differently. They don’t have the same surface albedo. Surface albedo is a measure that tells us how much solar radiation gets reflected back into space. Ocean water, for example, tends to absorb radiation. Its surface albedo is low. So that has a warming effect on the planet. But ice and snow reflect a lot of solar radiation. They have a higher albedo. It’s like how wearing white clothing can help you stay cooler in a hot day than wearing black clothing. Similarly, ice and snow, as well as being very cold themselves, have an additional cooling effect because they keep solar radiation from being absorbed.
Now once this process of reflection and cooling gets started, it can end up being self-perpetuating. The cooling increases the ice cover, which increases the surface albedo, so the climate gets even colder, causing more ice to form and so on. This is called the ice albedo feedback. Normally the process is kept in check by the ocean’s absorption of solar radiation, but according to the Snowball Earth hypothesis, the feedback loop didn’t stop. And so ice and snow were covering more and more land, cooling Earth’s surface more and more quickly, and got to the point where even the oceans were covered in ice.
Now for the thought of Earth as a giant snowball, I have to admit it has some dramatic appeal. And a number of geologists have come on board with it in fact, because there’s certainly evidence of extreme glaciation during the Cryogenian period. For example, in Oman, now Oman’s in the Middle East, right? So a hot climate today. Well, sedimentary rocks there provide clear evidence of glaciers in the Cryogenian period. But a new research study looked at the sedimentary rocks more closely. The technique they used, it’s useful to know this, because we will come across it again. What they look at is a measure called a chemical index of alteration. The chemical index of alteration is a gauge of chemical weathering of rock, which means the chemical changes that occurred in rock due to environmental conditions. A high rate of chemical weathering indicates a warm and humid environment. Well, a low rate of chemical weathering is consistent with cool and dry conditions. So in this rock in Oman, the chemical index of alteration suggests that the climate during the Cryogenian wasn’t consistent. There’s definitely evidence of periods with low rates of chemical weathering and therefore with cold conditions. But these alternate with intervals of high chemical weathering, which represent times of warmer weather, which means that there were periods when that deep-freeze broke. But how? If the Earth was completely frozen for a long period of time, I doubt warmer periods could have happened. The incoming solar radiation would have been reflected back, right? So the warmer periods indicate that at least some portions of the ocean weren’t frozen over.
选项
A、To describe changes in the chemical composition of the atmosphere
B、To measure the degree of chemical weathering of rocks
C、To find out how oceans affect global temperatures
D、To trace the movement of rock over time
答案
B
解析
题目询问化学蚀变指数的作用。教授说,化学蚀变指数是衡量岩石化学风化程度的指标。对应B项“衡量岩石的化学风化程度”。教授在讲座中明确提到了化学蚀变指数的作用,可排除A项“描述大气中化学成分的变化”、C项“查明海洋如何影响全球温度”和D项“追踪岩石随时间的变动”。
转载请注明原文地址:https://kaotiyun.com/show/MKfO777K
0
托福(TOEFL)
相关试题推荐
Completethenotesbelow.WriteONEWORDAND/ORANUMBERforeachanswer.SouthCityCyclingClubExampleNameofclubsecretary
Completethenotesbelow.WriteNOMORETHANTHREEWORDSAND/ORANUMBERforeachanswer.ExampleClearPointTelephoneCompany
ChooseTHREEletters,A-F.WhichTHREEthingsarethestudentsrequiredtosubmittotheirprofessor?AawrittensummaryBnote
Labelthemapbelow.WritethecorrectletterA-H,nexttoQuestions11-15.bikehire
Choosethecorrectletter,A,BorC.Thestudentbelievesthathighways
Choosethecorrectletter,A,BorC.Theprofessorsaysthatsuperhighways
Completethenotesbelow.WriteNOMORETHANTHREEWORDSAND/ORANUMBERforeachanswer.ExampleAnswerPurposeplacinga
Labelthemapbelow.WritethecorrectletterA-I,nexttoQuestions11-15.A______takesyoudowntotheharbourandaviewof
Labelthemapbelow.WritethecorrectletterA-I,nexttoQuestions11-15.A______standsinthe,centreofthepark.
StrategiesforeffectiveuseoflecturesDosome【L25】________【L26】________andsitwhereyoucanseeandheareasily.Be【L27】___
随机试题
经络气血逆乱,“厥气上逆”发为“霍乱”的是
牙拔除时不宜使用旋转力的牙为
局麻药的作用机制为
贾某受某电影制片厂之邀将自己的一部小说改编成电影文学剧本。改编完成后,导演陈某又请贾某为其主题歌谱曲,2005年9月,电影拍完后未获审查通过,此时贾某已出国无法联系。无奈,电影制片厂只好先后请王某、张某修改原剧本,其中张某仅在王某修改稿基础上略做了改动,但
下列各项中,属于单位内部会计控制制度的方法有()。
某企业以8%的年利率借得100000元,投资于某个寿命为5年的项目上,为使该项目有利可图,每年至少应收回的现金数额为()元。
产业政策的主要内容不包括()。
下面程序执行后,屏幕上显示的应是______。publicclassTestl0{publicstaticvoidmain(String[]args){
若窗体Frml中有一个命令按钮Cmdl,则窗体和命令按钮的Click事件过程名分别为()。
It’sonlyanarguablyverywillfulmisinterpretationoftheancientMayancalendartoconcludetheworldendson21December201
最新回复
(
0
)