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A、To prove earth’s continents were once joined together. B、To prove that the grain type within sandstone. C、To determine the act
A、To prove earth’s continents were once joined together. B、To prove that the grain type within sandstone. C、To determine the act
admin
2016-07-29
29
问题
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 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.
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 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 qui e 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. 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.
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.
22. What is the key to good analysis in geology?
23. What has been the conventional wisdom among geologists for quite some time?
24. What has produced some surprises among geologists?
25. What is one of the exciting possibilities for Uranium-Lead Dating?
选项
A、To prove earth’s continents were once joined together.
B、To prove that the grain type within sandstone.
C、To determine the actual particles in the sandstone.
D、To determine where the actual particles came from.
答案
A
解析
录音最后部分提到,铀铅测年存在一些令人兴奋的可能性。目前想到的一个可能性是铀铅测年可以更加确切地证实如下理论:地球上的所有太洲都曾结合在一起.并且最近才分裂开来。A项“可以证实大洲都曾结合在一起”为答案。B项中的“砂岩内部的颗粒类型”和C项中的“砂石中的实际颗粒”是课堂上通常研究的对象,故不选;D项“可以测量砂石中的颗粒来源”是观察砂石中实际颗粒的目的,与题目无关。
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大学英语六级
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