Listen to part of lecture in the Geology Class. (地质学）

OK, let's get started. Great! Today I want to talk about a way and in which we are able to determine how old a piece of land or some other geologic featuresfeature is - dating technics techniques. I'm going to talk about a particular dating technic 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 foundmental fundamental.

eh... um... take the Grand kenian Canyon for instance. Now, we geologists thought we had a pretty good idea of how the grandkenian Grand Canyon in the south-west southwestern united-states was formed. We knew that it was formed from sandstone that salisfy solidified somewhere between 150 and 300 million years ago. Before it salisfy solidified, they were it was just regular sand, the centurely Essentially, it was part of a vast desert.

And until just recently, most of us stalk thought the sand could had come from an ancient moutain range ralely farely close by at that flat flattened out overtime. That's been the conventional with the wisdom mount among geologists for quite some time. But now we've learned something different and quite surprising using a technic technique called youraininlate Uranium-Lead Dating.

I should say that youraininginlate dating Uranium-Lead Dating has been around for quite a while. But there have been some recent refilements refinements. I'll get it in into this in a minute. Anyway, youraininginlate Uranium-Lead Dating has produced some surprises. Two geogists geologists discovered that about half of the sand from the goundkanian Grand Canyon was actually one's part of the aberlegen mountian Appalachian Mountains. That's really eye opening news, since the aplengen Appalachian moutain ranges is, of course, thousands of kilometres kilometers to the east to of the grand kanian Grand Canyon. Sounds pretty unbelievable right?

Of course, the obvious question is, how did that sand end up so far west? The serie theory is that huge rivers and wind carry carried the sand west, where mixing it mixed with the sand that was already there. Well, this was a pretty revolutionary finding. eh.. um...And it was basically because of euraningemlatedating Uranium-Lead Dating. Why?

Well, is as everyone in this class should know, we usually look at the grand grain type within sandstorm sandstone, meaning the actual particles in the sandstorm 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 were what these two geoligists did. 

Yourainingemlatedating Uranium-Lead Dating allow them to go about it in an entirely different way. What they did was, they looked at the grains of observe corn Zircon in the sandstorm sandstone. Thecorn Zircon is a material that contains radio activity radioactive of raining Uranium, which makes it very useful for dating purposes. eh...

Thecorn Zircon starts off as motan megma molten magma, the hot lava from vocanoes. These megma magma burn crystalysis then crystallizes. And when thecorn Zircon crystalises crystallizes, the urinian Uranium inside begins to change into led Lead. So if you measure the amount of led in the cercorn gran Lead in the zircon grain, you can figure out when the gran grain was formed. After that, you can determine the age of cercorn Zircon from different mountain ranges.

Once you do that, you can compare the age of cercorn the Zircon in the sandstorm sandstone in your sample to the age of cercorn the Zircon in the mountains. If the age of cercorn the Zircon matches the age of one of your mountain ranges, that 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, yourainingemlateddating Uranium-Lead Dating was used to establish that half of the sandstone in the sample was formed at the same time that ground  the granite evlengenmoutain in the Appalachian Mountains was formed.

So because of this, these new way of doing euranianemlatedating Uranium-Lead Dating, we've been able to determine that one of the our major sumptions assumptions about the grand canean,  Grand Canyon was wrong. Like I said before, ??? Uranium-Lead Dating has been with us for a while.

But eh... um.... until recently, in order to do it, you really have to study million many individual grans grains. And it took a long time before you got results. It just wasn't very efficient. And it wasn't very agurate accurate.

But techinical advenserses has technical advances have cut down on the number grans grains you have to study, so you get the result your results faster. So operadect, um.... you rainingemlatedating I'll predict that Uranium-Lead Dating is going to become an increasingly popular dating method. There are a few pretty exiting exciting possibilities for you rainingemlatedating Uranium-Lead Dating. 

Here's the is one that comes to mind. You know, the serie theory that earth's contenents continents for one's join once joined together and only splitpart split apart relatively recently. Well, with ??dating  Uranium-Lead Dating we can could prove that more conclusively. If they show evidence of one's once having being been joined, that could really tell us a lot about the early history of the planet's geology.

What does the professor mainly discuss?
The difference in age among American mountain ranges.
√The importance of a technique used for dating geological materials.
The recent discovery of an ancient canyon.
A comparison of various minerals used for dating.

Before the use of uranium-lead analysis, where did most geologists think the Grand Canyon sandstone came from?
An ancient lake located in the American Southwest.
A desert that once connected two continents.
Sands carried by a river from the Appalachian Mountains.
√A nearby mountain range that had flattened out over time. 
（这一题很难做对，因为不一定听得出来，from an ancient mountain range fairly close by that flattened out over time.）
（我是听出来了，也不知道flattened out over time什么意思）（所以不可能选对）

拖选题，我还是第一次见到。

拿到山的zircon;

测不同zircon对应的样本；

拿山的zircon跟样本比对。

（这一题，直接pass）（你如果是第一次做的话，几乎没有做对的可能性，除非你对这个主题非常熟悉）

According to the professor, what change has caused uranium-lead dating to gain popularity recently?
lt can be performed outside a laboratory.
√lt can now be done more efficiently.
lt no longer involves radioactive elements.
lt can be used in fields other than geology.

Why does the professor talk about the breaking apart of Earth's continents?
√To give another example of how uranium-lead dating might be useful.
To explain how the Grand Canyon was formed.
To demonstrate how difficult uranium-lead dating is.
To disprove a theory about the age of Earth's first mountain ranges.

Listen again to part of the conversation/lecture. then answer the question.

What does the professor imply when he says this:

The class is easier than other geology classes.
√The class has already studied the information he is discussing.
Some students should take a course in geological dating techniques.
He will discuss the topic later in the class.