tpo1听力文本

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ers 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. UraniumLead 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 larva 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 pare 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 the 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, UraniumLead 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 UraniumLead Dating, we’ve been able to determine that one of our major assumptions about the Grand Canyon was wrong. Like I said before, UraniumLead 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 UraniumLead Dating is going to bee an increasingly popular dating method. There are a few pretty exciting possibilities for UraniumLead Dating. Here is one that es to mind. You know the theory that earth’s continents were once joined together and only split apart relatively recently? Well, with UraniumLead 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 pla’s geology. Section 2 Conversation Narrator Listen to part of a conversation between a student and his professor. Professor Hi Mathew, I’m glad you can e in today. You’ve been observing Mr. Grable’s thirdgrade class for your approaches to education paper, right? Student Hmmm, yes. I go over the Johnson Elementary School, you know, to watch Mr. Grable teach the children in class. It’s been amazing, I mean, I’m just learning so much from just watching him. I’m so glad the classroom observations are a requirement for the education program. I mean it’s like the best thing ever to prepare you to be a good teacher. Professor Well, I’m glad to see you feel that way, Mathew. You know, that’s the goal. So, I’ve been reading over your observation notes and I’m quite interested in what’s going on, in particular what’s the astronomy unit he’s been teaching. Student The astronomy unit? Professor It seems that Mr. Grable has mastered the interdisciplinary approach to teaching — the way we’ve been talking about in class. Student Oh! OK, yeah, so like when he was teaching them astronomy, he didn39。 t just teach them the names of the plas, he used it as a way to teach mythology. Professor Really! So, how did he do that? Student Well, some of the students could already name the plas, but they didn’t know that the names had any meaning — the stories behind them. Professor So, he… Student He introduced Greek and Roman mythology as a way of explaining. Like, you know, how like Jupiter’s the biggest pla, right, and how Jupiter was the name of the king of the gods in Roman mythology, right? So since Jupiter, the pla, is the largest pla in our solar system, it’s like the king of the plas, like Jupiter was the king of all the gods. Professor Oh, Mathew, that’s a great example. Student Yeah! And each student chose a pla and then did research on it to write a report and make a p。