考满分 toefl

1 .<-NARRATOR:->Listen to part of a lecture in an Earth science class.

旁白：请听一段地球科学课的讲座的节选。

1 .<-MALE PROFESSOR:->Let's review something from last week.

教授：我们先复习一下上周讲过的东西。

2 .We talked about an event that happened 65 million years ago... Anyone?

我们讲到了6500万年前发生的一个事件...有人记得吗？

1 .<-FEMALE STUDENT:->An asteroid hit Earth; um, well, we think an asteroid hit Earth... near the Yucatan peninsula in Mexico, and that wiped out all the dinosaurs.

学生：小行星撞击了地球。嗯……我们认为是有一个小行星撞击了地球，在墨西哥的尤卡坦半岛（Yucatan Peninsula）附近，这个事情使得恐龙灭绝了。

1 .<-MALE PROFESSOR:->Right, uh, I wouldn't say that we've got 100 percent proof, but there's very strong evidence that this is why that mass extinction occurred.

教授：对的。我不能说我们能百分百确定，但是的确有强有力的证据证明这就是大灭绝发生的原因。

2 .OK, but did you know there was an earlier extinction- far greater than the one that killed off the dinosaurs?

好的。但是你们知道吗，在恐龙灭绝的那场大灭绝之前，还有一场更大的灭绝。

3 .It was what we call the Permian extinction.

它被我们称为二叠纪大灭绝。

1 .Now, way back about 290 million years ago-at the beginning of the Permian period, there was just one big continent, a supercontinent.

现在，追溯到29000万年前，在二叠纪的开端，当时只有一个大洲，一个超级大洲。

2 .And as the climate warmed up, plant and animal species began to diversify profusely.

然后随着气候变暖，动植物开始变得多样化。

3 .So life during the Permian period was abundant and diverse.

所以二叠纪的物种是数量丰富且种类繁多的。

1 .But about 250 million years ago, the Permian period ended with a rapid mass extinction.

但是在25000万年前，一场迅速的物种大灭绝终结了二叠纪

2 .Something happened that wiped out 75 percent of the land animals and over 95 percent of ocean life.

某些事情一次性使得75%的陆地动物和95%的海洋生物灭绝。

1 .So what was it?

所以这到底是什么事情呢？

2 .What could have caused this?

什么导致了这场灭绝呢？

3 .Well, with all the evidence that it was an asteroid that led to the dinosaur extinction, we began asking ourselves: Is it possible that another asteroid... much earlier... caused the Permian extinction?

所有的证据显示，小行星撞击地球导致了恐龙的灭绝。我们就开始问自己了：可不可能是更早时候也有一颗小行星撞击了地球，导致了二叠纪的灭绝？

4 .And so researchers have been looking for an impact crater.

研究者们就开始寻找陨石坑。

1 .<-FEMALE STUDENT:->I thought the Permian extinction was caused by a decline in seawater oxygen levels.

学生：我以为二叠纪大灭绝是由海水氧气含量降低导致的。

2 .Isn't that what's in the textbook?

这不是课本上写的吗？

1 .<-MALE PROFESSOR:->But don't forget, the textbook makes it very clear-that's only a theory.

教授：但是别忘了，课本上也写了这仅仅是个理论。

1 .<-MALE STUDENT:->And it mentions something about volcanic eruptions, too.

学生：课本上也提到了一些关于火山爆发的事情。

1 .<-MALE PROFESSOR:->It does. But now, this new theory has led to a search for evidence of an asteroid impact.

教授：是的，但是现在的新理论导致了一场寻找陨石坑证据的活动。

2 .And one place of interest is a region called Wilkes Land in eastern Antarctica.

有趣的是，一个南极洲东边叫做威尔克斯区(Wilkes Land)的地方。

1 .A few years ago, a researcher reported a strange anomaly beneath the ice in Wilkes Land- evidence of what may be a mascon.

几年前，一个研究者报告说威尔克斯区(Wilkes Land)下面的冰层有异常情况，可能是一个质量密集现象。

2 .That's just short for "mass concentration."

这是质量浓度的简写。

1 .When an asteroid hits Earth, when it slams into Earth's crust, we think that causes molten rock from deep below the surface to rise up into the impact area- sort of like if you bump your head, you get a big lump under the skin... fluid makes the area swell.

当小行星撞击地球时，它撞入地球的外壳，我们认为它会导致地球内部的熔化的岩石上升冲入陨石坑,就像是你撞了头，你的皮肤下面就会出现肿块，液体使得那块地方水肿了。

2 .Anyway, the material flowing up from below the crust is more dense than the crust itself.

不管怎样，从地球内部流上来的液体比地壳本身密度更高。

3 .So that's how we get a mascon- a spot in the crust with newer crust material that's more dense than the material all around it.

我们这样就得到了一个陨石坑，它就是一个地壳上的地点，比周围的物质更新，密度更高。

1 .There are lots of mascons on the Moon too, where a mascon's density causes a small increase in the local gravity that can be measured and mapped by orbiting spacecraft.

月球上也有很多的陨石坑,这些陨石坑导致其周围地区的引力变大，进而可以通过沿轨道运行的航天器来测量和定位。

2 .And where do these mascons tend to be found?

那么哪里可以找到这些陨石坑呢？

3 .In the centers of impact craters on the Moon's surface.

可以在月球表面的陨石坑中心找到它们。

1 .But back to Wilkes Land...

让我们回到威尔克斯区(Wilkes Land)。

2 .We're not certain that the mascon there... what might be a mascon... was actually caused by the impact of an asteroid, but there does seem to be evidence: researchers noticed a gravity anomaly similar to those on the Moon.

我们并不确定有陨石坑……不确定什么可能是一个陨石坑……不确定这个坑确实是因为小行星撞击形成的，但是我们的确有一些证据,研究者们注意到了类似于月球上的重力异常现象。

3 .And the spot where the gravity readings are especially high- this is right in the middle of a 500-kilometer-wide circular ridge- what could be part of an old impact crater.

在那些重力特别大的地点……刚好在500千米的一个圆形山脊的中间，那就可能是一个老的陨石坑了。

1 .And if there was an asteroid impact there in Wilkes Land, the next question is- Did it happen 250 million years ago?

如果真的在威尔克斯区（Wilkes Land）里有个陨石坑，那么下一个问题就是：它是在25000万年以前形成的吗？

2 .Because that would put it when in geologic history?

因为这个问题会帮我们判断它所处的地质历史位置。

1 .At the end of the Permian period, right when all those animals went extinct.

在二叠纪末期？正好是在那些动物灭绝的时候。

1 .Exactly.

确实。

1 .But... can't researchers figure that out by studying the rocks there in Wilkes Land... where this impact supposedly took place?

但是研究者不能通过研究威尔克斯区（Wilkes Land)里面的岩石来确定这个时间……这个小行星撞击发生的时间？

1 .Well, to get to anything from that long ago, we'd have to drill down through about a mile... about 1.6 kilometers... of solid ice that covers the area today.

为了从那么久远以前发现一些东西，我们需要深入地下大约一英里，大致是1.6公里，冲破覆盖这片地区的坚硬冰层去探索。

2 .And that's not likely to happen.

这个是不大可能的。

1 .But speaking of rocks, I should mention that Wilkes Land is not the only place of interest here.

但是说起岩石，我必须提到，威尔克斯区(Wilkes Land)并不是唯一让研究者感兴趣的地点。

2 .There's another called the Bedout High...off the coast of Australia.

还有一个叫做Bedout High的地方，远离澳大利亚的海岸。

1 .And we have rock samples from the Bedout High- some apparently of extraterrestrial origin.

我们有那里的岩石样本,这些岩石样本里有一些来自地球外的物质。

2 .I mean, they show the effects of extreme temperatures and pressures- the level of extremes produced only by an impact.

我的意思是，它们展现出极度高温和高压的影响，这种情况只会在小行星撞击地球的时候出现。

3 .And as for their age..., well, they do, in fact, date back to about 250 million years ago!

至于它们的年龄嘛，实际上可以追溯回25000万年前。