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旁白：请听一段关于地质学的讲座。

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

教授：现在在美国西部某些地方发现了一些有趣的洞穴，尤其是在国家公园一带。

Professor: Now, there're some pretty interesting caves in parts of the western United States, um, specially in National Parks.

有一个地方发现了超过100个洞穴，其中一个的规模为世界最大。

There's one park that has over a hundred caves including some of the largest ones in the world.

这些洞穴中，比较有趣的一个名叫拉曲吉亚洞穴。

One of the more interesting ones is called Lechuguilla Cave.

拉曲吉亚在近几十年被发掘过几次。

Lechuguilla's been explored a lot in recent decades.

我觉得它是一处让人激动的遗址。

你们的书中只是大概提了一下。

It was mentioned only briefly in your books.

有人记得书里是怎么描述它的吗？艾伦？

So can anyone remember what it said? Ellen?

女学生：书里说它是美国最深的石灰岩洞穴？

Female Student: It's the deepest limestone cave in the US?

教授：正确。不过它的深度、长度不仅是我国第一，而且更是世界第一。

Professor: That's right. It's one of the longest and deepest limestone caves not just in the country but in the world.

女学生：嗯，它是由于硫酸的腐蚀而形成的，对吗？

Female student: Well, it was formed because of sulfuric acid, right?

教授：是那样的。对，事情是，当地下深处有油类囤积和细菌微生物时，就会有腐蚀。

Professor: That's it, yeah, what happens is you have deep underground oil deposits and there are bacteria.

Here, let me draw a diagram. (Surface, Rock, Rock and water, Oil and bacteria)

地下石灰岩的一部分被地下水淹没。我们假设这些波浪线代表了岩石的裂缝。

Part of the limestone rock layers permeated by water from below. Those curly lines are supposed to be cracks in the rock.

石油出现的位置，在地下水位线和岩石之下。

细菌靠分解石油维持生命，在这个过程中，就会有硫化氢释放出来。

Bacteria feed on this oil and release hydrogen sulfide gas.

硫化氢上升，与地下水中溶解的氧气混合，渗入石灰岩的缝隙中。

This gas is hydrogen sulfide, rises up and mixes with oxygen in the underground water that sits in the cracks and fissures in the limestone.

并且当硫化氢与水中的氧气反应时，会产生硫酸，对吧？

And when hydrogen sulfide reacts with the oxygen in the water, the result of that is sulfuric acid. OK?

硫酸对石灰岩的腐蚀性是极强的。所以这个裂缝就会越来越大，逐渐地就会有一条通道沿着岩石的断裂层形成。这个过程全部是发生在地下。

Sulfuric acid eats away at limestone very aggressively, so you get bigger cracks and then passageways being formed along the openings in the rock, and it's all underground.

男学生：这样的话，地下水……难道它是不流动的，对吗？它是静止的？

Male student: So that water, it's not flowing, right? It's still?

教授：是的，所以世界上有两种类型的石灰岩洞穴。

Professor: Yes, so there's two kinds of limestone caves.

百分之九十的洞穴的表面都有水，比如小溪，瀑布等各种沿着岩石缝隙流动的水流。

In about 90 percent of them, you have water from the surface, streams, waterfall, or whatever, moving water that flows through cracks found in limestone.

腐蚀岩石，形成通道的因素就在于这些水流自身。

It's the moving water itself that wears away at the rock and makes passageways.

而且，这些地表水流中，存在弱酸，比如碳酸，而不是硫酸。这种酸也能腐蚀岩层。

Also, in surface water there's a weak acid, carbonic acid, not sulfuric acid but carbonic acid that helps dissolve the rock.

依靠这种弱酸的帮助和水流的冲击力，大部分石灰岩洞穴形成了。

With a little help from this carbonic acid, moving water forms most the world's limestone caves.

几年前我做这项研究时，我探访了其中几个比较典型的洞穴；它们都很潮湿，你们也知道这是因为水流的缘故。

When I was researching this for a study a few years ago, I visited a couple of these typical limestone caves, and they were all very wet, you know, from streams and rivers.

总之，这些水流凿穿了岩石，造成了这些洞穴及其内部结构。

This flowing water carved out the caves and the structures inside them.

男学生：不过这些洞穴中不包括拉曲吉亚？

教授：拉曲吉亚干燥得像块硬骨头！

嗯，这个比喻有些夸张了。不过，我们可以很稳妥地说，是硫酸而非水流使得拉曲吉亚等洞穴成形。

Well, that might be a bit of an exaggeration, but, it's safe to say that it's sulfuric acid and not moving water that formed Lechuguilla cave and those few other ones like it.

实际上，没有证据表明水流曾在拉曲吉亚附近进出过。

In fact, there's no evidence that flowing water has ever gone in or out of the cave.

所以，拉曲吉亚洞穴就像一座迷宫，里面到处都是通道。

So, it's like a maze, you have passageways all around.

There are wide passages, narrow ones, at all different depths, like underground tunnels in the limestone.

并且，由于它是在地下形成的而不是由地表水流形成，某些通道完全没有与地面接通。

And since they were created underground, and not from flowing surface water, not all these passageways have an opening to the outside world.

并且……嗯，有证据表明水流与拉曲吉亚没有丝毫关系。

And, and there's other evidence that flowing water wasn't involved in Lechuguilla.

我们讲过，硫酸可以溶解石灰岩，是吧？

We've said that sulfuric acid dissolves limestone, right?

硫酸还有什么别的功能呢？保罗？

男学生：嗯，它会遗留下一些残渣，并且……

Male student: Uh, it leaves a  chemical residue, um...

女学生：这些残渣就是石膏，对吗？

教授：正确，你们会在拉曲吉亚洞穴中发现许多沉积下来的石膏。

Professor: Yeah. You'll find lots of gypsum deposited at Lechuguilla.

同时，我们知道，石膏是可以溶解在水中的。所以如果拉曲吉亚附近有水流存在的话，它就会使石膏溶解。

And as we know, gypsum is soluble in water, so if there were flowing water in the cave, it would dissolve the gypsum.

这就是为什么我们会得出拉曲吉亚是为数不多的、并非因水流形成的洞穴之一。

This is part of what led us to the realization that Lechuguilla is in that small group of waterless caves.

现在拉曲吉亚洞穴的形成已经停滞了。

And Lechuguilla's pretty much dormant now.

它现在已经不再有进一步变化了。

不过，也有其他与之相似的洞穴依旧进行着这个过程，比如，在墨西哥就有一个。

But, there's other ones like it, for example, in Mexico, that are forming.

当研究人员探索这些洞穴时，他们看到、闻到硫酸，和像……的气体，

And when cave researchers go to explore them, they see and smell the sulfuric acid and gases at work.

嗯……，想想臭鸡蛋的味道吧！

Phew, now, something else, think of rotten eggs.

而且，不仅是只有这种味道，研究员还得带上专门的面具，使自己和这种气体隔绝开。保罗，你有问题吗？

And it's not just the smell. Explorers even need to wear special masks to protect themselves from gases in these caves. OK, um, Paul?

男学生：嗯，这些洞穴里面是什么样子的？

Male student: Yeah, how about what these caves look like on the inside?

教授：嗯，里面形成的物质……里面的确有些东西。

Professor: Well, the formations are really something.

不过这些物质各式各样好像世界其它地方都没有。

Um, there are such varieties there, like, nothing anywhere else in the world.

有些看上去很像精心设计的装饰物，其中相当一部分都是由石膏构成的，高度达到了20英尺。

Some of them are elaborate looking like decorations, and a lot of them are made of gypsum and could be up to twenty feet long.

The professor mentions parts of the process involved in the formation of Lechugilla Cave. Indicate which of the statements below describe part of the process.

According to the professor, what substance found in surface water is important for the formation of typical limstone caves?

What does the presence of gypsum in Lechuguilla Cave indicate?

What can be inferred from be fact that Lechuguilla Cave is no longer forming?

What does the professor mean when he says this:

Narrator: 
Listen to a part of lecture in a geology class. 
Professor: 
Now there are some pretty interesting caves in parts of the western United States, especially in national parks. There is one part that has over a hundred caves, including some of the largest ones in the world. One of the more interesting ones is called Lechuguilla Cave. Lechuguilla has been explored a lot in recent decades. It’s a pretty exciting place I think. It was mentioned only briefly in your books. So can anyone remember what it said? Ellen? 
Male Student: 
It’s the deepest limestone cave in the U.S.? 
Professor: 
That’s right. It’s one of the longest and deepest limestone caves not just in the country but in the world. Now, what else? 
Male Student: 
Well, it was formed because of sulfuric acid, right? 
Professor: 
That’s it. Yeah, what happens is you have deep underground oil deposits and there are bacteria. Here let me draw a diagram. Part of the limestone rock layer is permeated by water from below. Those curly lines are supposed to be cracks in the rock. Below the water table and rock is oil. Bacteria feed on this oil and release hydrogen sulfide gas. This gas is hydrogen sulfide, rises up and mixes with oxygen in the underground water that sits in the cracks and fissures in the limestone. And when hydrogen sulfide reacts with the oxygen in the water, the result of that is sulfuric acid, Ok? Sulfuric acid eats away at limestone very aggressively. So you get bigger cracks and then passageways being formed along the openings in the rock and it’s all underground. Ah yes, Paul? 
Male Student: 
So that water... It’s not flowing, right? It’s still? 
Professor: 
Yes, so there’s two kinds of limestone caves. In about 90 percent of them, you have water from the surface, streams, waterfall or whatever - moving water that flows through cracks found in the limestone. It’s the moving water itself that wears away at the rock and makes passageways. 
Also, in surface water, there is a weak acid, carbonic acid, not sulfuric acid, but carbonic acid that helps dissolve the rock. With a little help from this carbonic acid, moving water forms most of the world’s limestone caves. When I was researching this for a study a few years ago, I visited a couple of these typical limestone caves, and they were all very wet, you know, from streams and rivers. This flowing water carved out the caves and the structures inside them. 
Male Student: 
But not Lechuguilla? 
Professor: 
Dry as a bone. Well, that might be a bit of an exaggeration. But it’s safe to say that it’s sulfuric acid and not moving water that formed Lechuguilla cave and those few other ones like it. In fact, there is no evidence that flowing water has even gone in or out of the cave. So, it’s like a maze. You have passageways all around. There are wide passages, narrow ones at all different depths, like underground tunnels in the limestone. And, since they were created underground and not from flowing surface water, not all these passageways have an opening to the outside world. And.. .and there is other evidence that flowing water wasn’t involved in Lechuguilla. We’ve said that sulfuric acid dissolves limestone, right, and forms the passageways? What else does sulfuric acid do? Paul? 
Male Student: 
Ah, leaves a chemical residue ... um... 
FeMale Student: 
Gypsum, right? 
Professor: 
Yep, you’ll find lots of gypsum deposited at Lechuguilla. And, as we know, gypsum is soluble in water. So if there were flowing water in the cave, it would dissolve the gypsum. This is part of what led us to the realization that Lechuguilla is in that small group of waterless caves. And Lechuguilla is pretty much dormant now. It’s not really forming any more. But, there is other ones like it, for example, in Mexico, that are forming. And when cave researchers go to explore them, they see and smell, the sulfuric acid and gases of...er...phew...now, something else, think of rotten eggs. And, it’s not just the smell. Explorers even need to wear special masks to protect themselves from the gases in these caves. OK? Paul. 
Male Student: 
Yeah, how about what these caves look like on the inside? 
Professor: 
Well, the formations.. .there is really something. There’s such variety there, like nothing anywhere else in the world, some of them are elaborate looking, like decorations. And a lot of them are made of gypsum and could be up to 20 feet long. It’s pretty impressive. 
Professor: 
Yes, so there are two kinds of limestone caves. In about 90 percent of them, you have water from the surface, streams, waterfall or whatever - moving water that flows through cracks found in the limestone. It’s the moving water itself that wears away at the rock and makes passageways. 
Also, in surface water, there is a weak acid, carbonic acid, not sulfuric acid, but carbonic acid that helps dissolve the rock. With a little help from this carbonic acid, moving water forms most of the world’s limestone caves. When I was researching this for a study a few years ago, I visited a couple of these typical limestone caves, and they were all very wet, you know, from streams and rivers. This flowing water carved out the caves and the structures inside them. 
Professor: 
Dry as a bone. Well, that might be a bit of an exaggeration. But it’s safe to say that it’s sulfuric acid and not moving water that formed Lechuguilla cave and those few other ones like it. In fact, there is no evidence that flowing water has even gone in or out of the cave. So, it’s like a maze. You have passageways all around. There are wide passages, narrow ones at all different depths, like underground tunnels in the limestone. And, since they were created underground and not from flowing surface water, not all these passageways have an opening to the outside world. And.. .and there is other evidence that flowing water wasn’t involved in Lechuguilla. We’ve said that sulfuric acid dissolves limestone, right, and forms the passageways? What else does sulfuric acid do? Paul? 
Male Student: 
Ah, leaves a chemical residue ... um... 
FeMale Student: 
Gypsum, right? 
Professor: 
Yep, you’ll find lots of gypsum deposited at Lechuguilla. And, as we know, gypsum is soluble in water. So if there were flowing water in the cave, it would dissolve the gypsum. This is part of what led us to the realization that Lechuguilla is in that small group of waterless caves. And Lechuguilla is pretty much dormant now. It’s not really forming any more. But, there is other ones like it, for example, in Mexico, that are forming. And when cave researchers go to explore them, they see and smell, the sulfuric acid and gases of...er...phew...now, something else, think of rotten eggs. And, it’s not just the smell. Explorers even need to wear special masks to protect themselves from the gases in these caves. OK? Paul. 
Professor: 
Yep, you’ll find lots of gypsum deposited at Lechuguilla. And, as we know, gypsum is soluble in water. So if there were flowing water in the cave, it would dissolve the gypsum. This is part of what led us to the realization that Lechuguilla is in that small group of waterless caves. And Lechuguilla is pretty much dormant now. It’s not really forming any more. But, there is other ones like it, for example, in Mexico, that are forming. And when cave researchers go to explore them, they see and smell, the sulfuric acid and gases of...er...phew...now, something else, think of rotten eggs. And, it’s not just the smell. Explorers even need to wear special masks to protect themselves from the gases in these caves. OK? Paul. 
Professor: 
Dry as a bone. Well, that might be a bit of an exaggeration. But it’s safe to say that it’s sulfuric acid and not moving water that formed Lechuguilla cave and those few other ones like it. In fact, there is no evidence that flowing water has even gone in or out of the cave. So, it’s like a maze. You have passageways all around. There are wide passages, narrow ones at all different depths, like underground tunnels in the limestone. And, since they were created underground and not from flowing surface water, not all these passageways have an opening to the outside world. And.. .and there is other evidence that flowing water wasn’t involved in Lechuguilla. We’ve said that sulfuric acid dissolves limestone, right, and forms the passageways? What else does sulfuric acid do?