托福TPO01精听讲义 | 讲座2:Uranium-Lead Dating

Part I

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 going to talk about a particular dating technique. Why? Good dating is a 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. Um… Take the Grand Canyon for instance.

1. date|deɪt|

verb. to show or find out when (something) was made or produced 确定...的年代

E.g.:Scientists use various techniques to date fossils.

        科学家们用各种技术去鉴定化石的年代。

2. fundamental|ˌfʌndəˈmentl|

adj. serious and very important; affecting the most central and important parts of sth十分重大的；根本的

E.g.:A fundamental change in the organization of health services was required.

公共医疗在组织上需要有一个根本性的变革。

Part II

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 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 will get into this in a minute. Anyway, Uranium-Lead Dating has produced some surprises.

直到最近，我们大多数人还认为这些沙子来自一个距离相当近的古老山脉，随着时间的推移，山脉变得平坦。

1.solidify|səˈlɪdɪfaɪ|

verb. to become solid; to make sth solid （使）凝固，变硬，变得结实

E.g.:The mixture will solidify into toffee.

这种混合物凝固后就成了太妃糖。

2. conventional wisdom

the view or belief that most people hold大多数人的看法；普遍信念

E.g.:Conventional wisdom has it that riots only ever happen in cities.

人们普遍认为，只有城市里才发生暴乱。

3. around|əˈraʊnd|

adv.present in a place; available 出现；现有；可用

E.g.:Digital television has been around for some time now.数字电视已经面市一段时间了。

4. refinement|rɪˈfaɪnmənt|

noun.a small change to sth that improves it（精细的）改进，改善

E.g.:This particular model has a further refinement.

这一款式又有了进一步的改进。

Part III

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. Um… 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.

此理论是巨大的河流和风将沙子带到西边，与那里已经存在的沙子混在一起。

好吧，本班的每个人都应该知道，我们通常会查看砂岩中的颗粒类型，即砂岩中的实际颗粒，以确定它的来源。

1. revolutionary |ˌrevəˈlu:ʃənəri|

adj. involving a great or complete change 彻底变革的；巨变的

E.g.:His playing as a trumpet player was quite revolutionary.

他的小号演奏独创一格。

2. up to a point

to some extent; to some degree but not completely在某种程度上

E.g.:Competition is good but only up to a certain point.

竞争是好的，但只在某种程度上。

Part IV

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. 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 the 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.

如果该锆石的年龄与你的一个山脉的年龄相匹配，那么这就意味着该砂岩实际上曾经是此山脉的一部分。大家都能跟上我讲的吗？

1. go about

to continue to do sth; to keep busy with sth 继续做某事；忙于某事

E.g.:Despite the threat of war, people went about their business as usual.

虽然战争在即，人们照常忙着自己的事。

2. start off

to begin by doing or being sth首先进行；一开始是

E.g.:The leaves start off green but turn red later.

树叶起先是绿色，到后来会变红。

3. crystallize|ˈkrɪstəlaɪz|

verb. (technical 术语) to form or make sth form into crystals（使）形成晶体，结晶

E.g.:The salt crystallizes as the water evaporates.

盐在水分蒸发时结晶。

Part V

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, um…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 Uranium-Lead Dating is going to become an increasingly popular dating method. There are a few pretty exciting possibilities for Uranium-Lead Dating. Here is 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.

因此，在这种情况下，使用铀铅测年法确定样品中一半的砂岩是在阿巴拉契亚山脉的花岗岩形成的同时而形成的。

1. individual|ˌɪndɪˈvɪdʒuəl|

adj. considered separately rather than as part of a group 单独的；个别的

E.g.:The minister refused to comment on individual cases.

那位部长拒绝对具体个案发表评论。

2. advance |ədˈvɑ:ns|

noun. progress or a development in a particular activity or area of understanding进步；进展

E.g.:We live in an age of rapid technological advance.

我们生活在技术迅猛发展的时代。

3. conclusive|kənˈkluːsɪv|

adj. proving sth, and allowing no doubt or confusion结论性的；不容置疑的；确凿的

E.g.:Research on the matter is far from conclusive.

对这一问题的研究还远远没有定论。