Uranium-Lead Dating托福听力原文翻译及问题答案

Uranium-Lead Dating托福听力原文翻译及问题答案,关于这个问题中国教育在线外语平台小编就简单为大家说一下。

一、Uranium-Lead Dating托福听力原文：

Narrator:Listen to part of a lecture in a geology class.

MALE PROFESSOR:OK,let's get started.Great—today I want to talk about a way in which we are able to determine how old a piece of land or some other geologic feature is.Dating techniques.I'm gonna talk about a particular dating technique.Why?Good dating is key to good analysis.In other words,if you want to know how a land formation was formed,the first thing you probably want to know is how old it is.It's fundamental.

Uh,take the Grand Canyon for instance.Now,we geologists thought we had a pretty good idea of how the Grand Canyon in the southwestern United States was formed.We knew that it was formed from sandstone that solidified somewhere between 150 and 300 million years ago.Before it solidified,it was just regular sand—essentially,it was part of a vast desert.

And,uh,until just recently most of us thought the sand had come from an ancient mountain range fairly close by that flattened out over time.That's been the conventional wisdom among geologists for quite some time.But now we've learned something different and quite surprising using a technique called uranium-lead dating.

I should say that uranium-lead dating has been around for quite a while,but there have been some recent refinements—I'll get into this in a minute.Anyway,uranium-lead dating has produced some surprises.Two geologists discovered that about half of the sand from the Grand Canyon was actually once part of the Appalachian Mountains.That's really eye-opening news,since the Appalachian Mountain range is,of course,thousands of kilometers to the east of the Grand Canyon.Sounds pretty unbelievable,right?

Of course,the obvious question is,how did that sand end up so far west?The theory is that huge rivers and wind carried the sand west,where it mixed in with the sand that was already there.Well,this was a pretty revolutionary finding,uh,and it was basically because of uranium-lead dating.Why? 

Well,as everyone in this class should know,we usually look at the grain type within sandstone,meaning the actual particles in the sandstone,to determine where it came from.You can do other things,too,like look at the wind or water that brought the grains to their location and figure out which way it was flowing.But that's only useful up to a point,and that's not what these two geologists did.

Uranium-lead dating allowed them to go about it in an entirely different way.What they did was they looked at the grains of zircon in the sandstone.Zircon is a material that contains radioactive uranium,which makes it very useful for dating purposes.

Uh,zircon starts off as molten magma,the hot lava from volcanoes.This magma then crystallizes.And when zircon crystallizes,the uranium inside it begins to change into lead.So,if you measure the amount of lead in a zircon grain,you can figure out when the grain was formed.After that,you can determine the age of zircon from different mountain ranges.

Once you do that,you can compare the age of the zircon in the sandstone in your sample to the age of the zircon in the mountains.If the age of the zircon matches the age of one of your mountain ranges,then it means the sandstone actually used to be part of that particular mountain range.Is everybody with me on that?Good.So in this case,uranium-lead dating was used to establish that half of the sandstone in the samples was formed at the same time the granite in the Appalachian Mountains was formed.

So,because of this—this new way of doing uranium-lead dating,we've been able to determine that one of our major assumptions about the Grand Canyon was wrong.Like I said before,uranium-lead dating has been with us for a while,but,uh,until recently,in order to do it,you really had to study many individual grains,and it took a long time before you got results.It just wasn't very efficient and it wasn't very accurate.

But technical advances have cut down on the number of grains you have to study,so you get your results faster.So I'll predict that,uh,uranium-lead dating is going to become an increasingly popular dating method.There are a few pretty exciting possibilities for uranium-lead dating.

Here's one that comes to mind.You know,the theory that Earth's continents were once joined together and only split apart relatively recently?Well,with uranium-lead dating,we could prove that more conclusively.If they show evidence of once having been joined,that could really tell us a lot about the early history of the planet's geology.

二、Uranium-Lead Dating托福听力中文翻译：

旁白：听地质学课上的部分讲座。

男教授：好的，我们开始吧。很好，今天我想谈谈一种我们能够确定一块土地或其他地质特征的年代的方法。约会技巧。我要谈谈一种特殊的约会技巧。为什么？良好的约会是良好分析的关键。换言之，如果你想知道一块土地是如何形成的，你可能首先想知道它的年代。这是最基本的。

呃，以大峡谷为例。现在，我们地质学家认为我们对美国西南部的大峡谷是如何形成的有了很好的了解。我们知道它是由1.5亿到3亿年前某处固化的砂岩形成的。在它凝固之前，它基本上只是普通的沙子，它是一片广袤沙漠的一部分。

而且，直到最近，我们大多数人还认为这些沙子来自一座古老的山脉，离那座山脉很近，随着时间的推移，山脉逐渐变平。这一直是地质学家的传统智慧。但现在我们通过一种名为铀铅测年的技术，学到了一些不同的、非常令人惊讶的东西。

我应该说铀铅测年已经存在了很长一段时间，但最近有一些改进，我马上就要开始讨论。无论如何，铀铅测年法产生了一些令人惊讶的结果。两位地质学家发现，大峡谷中大约一半的沙子实际上曾经是阿巴拉契亚山脉的一部分。这真是一个令人大开眼界的消息，因为阿巴拉契亚山脉当然在大峡谷以东数千公里处。听起来很不可思议，对吧？

当然，一个明显的问题是，这些沙子怎么会流到这么远的西部？该理论认为，巨大的河流和风将沙粒带到了西部，在那里沙粒与已经存在的沙粒混合在一起。这是一个革命性的发现，基本上是因为铀铅测年。为什么?

这门课上的每个人都应该知道，我们通常会观察砂岩中的颗粒类型，也就是砂岩中的实际颗粒，以确定其来源。你也可以做其他事情，比如看看把谷物带到它们所在位置的风或水，找出它们的流向。但这只在一定程度上有用，这两位地质学家并没有这样做。

铀铅测年使他们能够以完全不同的方式进行。他们所做的是观察砂岩中的锆石颗粒。锆石是一种含有放射性铀的材料，这使得它在测年方面非常有用。

锆石开始时是熔融的岩浆，是来自火山的热熔岩。然后岩浆结晶。当锆石结晶时，里面的铀开始变成铅。所以，如果你测量锆石颗粒中铅的含量，你就能知道颗粒是什么时候形成的。之后，你可以确定不同山脉锆石的年龄。

一旦你这样做了，你就可以比较你样本中砂岩中锆石的年龄和山脉中锆石的年龄。如果锆石的年龄与你的一座山脉的年龄相匹配，那么这意味着砂岩实际上曾经是那座特定山脉的一部分。大家都同意我的看法吗？好的因此，在这种情况下，铀铅测年被用来确定样品中一半的砂岩是在阿巴拉契亚山脉花岗岩形成的同时形成的。

因此，由于这种新的铀铅测年方法，我们能够确定我们对大峡谷的一个主要假设是错误的。正如我之前所说，铀铅测年已经存在了一段时间，但是，直到最近，为了做到这一点，你真的需要研究许多单个的颗粒，而且需要很长时间才能得到结果。只是效率不高，也不太准确。

但是技术进步减少了你必须研究的谷物数量，所以你可以更快地得到结果。所以我预测，铀铅定年将成为一种越来越流行的定年方法。铀铅测年有一些非常令人兴奋的可能性。

我想到了一个。你知道，地球各大洲曾经连接在一起，只是最近才分开的理论吗？嗯，用铀铅测年法，我们可以更确切地证明这一点。如果他们有证据表明曾经有人加入，那真的可以告诉我们很多关于这颗行星早期地质的历史。

三、Uranium-Lead Dating托福听力问题：

Q1:1.What does the professor mainly discuss?

A.The differences in age among American mountain ranges

B.The importance of a technique used for dating geological materials

C.The recent discovery of an ancient canyon

D.A comparison of various minerals used for dating

Q2:2.Before the use of uranium-lead analysis,where did most geologists think the Grand Canyon sandstone came from?

A.An ancient lake located in the American Southwest

B.A desert that once connected two continents

C.Sands carried by a river from the Appalachian Mountains

D.A nearby mountain range that had flattened out over time

Q3:3.In the talk,the professor describes the sequence of uranium-lead dating.Summarize the sequence by putting the events in the correct order.

A.Zircon in the sandstone is matched to the zircon in a particular mountain range

B.The amount of lead in sandstone zircon is measured.

C.The age of zircon in a sandstone sample is determined.

Q4:4.According to the professor,what change has caused uranium-lead dating to gain popularity recently?

A.It can be performed outside a laboratory.

B.It can now be done more efficiently.

C.It no longer involves radioactive elements.

D.It can be used in fields other than geology.

Q5:5.Why does the professor talk about the breaking apart of Earth's continents?

A.To give another example of how uranium-lead dating might be useful

B.To explain how the Grand Canyon was formed

C.To demonstrate how difficult uranium-lead dating is

D.To disprove a theory about the age of Earth's first mountain ranges

Q6:6.What does the professor imply when he says this:

A.The class is easier than other geology classes

B.The class has already studied the information he is discussing

C.Some students should take a course in geological dating techniques

D.He will discuss the topic later in the class

四、Uranium-Lead Dating托福听力答案：

A1:正确答案：B

A2:正确答案：D

A3:正确答案：BCA

A4:正确答案：B

A5:正确答案：A

A6:正确答案：B

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