The K-T boundary marks the end of the age of dinosaurs, and the beginning of the age of mammals.
KT界限层标志着恐龙时代的终点和哺乳动物时代的开端。
But does the K-T boundary really signify the absolute end of all dinosaurs?
不过KT界限层真的标志着所有恐龙的彻底消亡吗？
Many experts believe that dinosaurs, are still among us.
很多专家认为恐龙仍生活在我们之中。
At 65 and a half million years ago, the age of dinosaurs came to an end.
在六千五百万年前，恐龙的纪元走向终结。

After that point, mammals were the dominant land living creature.
在那以后，哺乳动物是陆地上的统治性生物。
However, it's important to remember that although the age of dinosaurs came to an end, the dinosaurs themselves did not.
但是，不要忘了，尽管恐龙的时代走到了终点，恐龙本身并没有。
Well, it turns out that one branch of that group survived, and that's the great group of birds.
其实它们中的一个分支得以幸存，那就是如今繁多的鸟类。
Birds themselves are the descendants of creatures very closely related to things like Deinonychus and Utahraptor, and so birds are, by definition, part of the dinosaur group.
鸟类的祖先与恐爪龙和犹他盗龙这类恐龙亲缘关系很近，所以从定义来说鸟类是恐龙族群的一部分。
So the dinosaur survived, but I have to say, all the really cool ones died out.
所以恐龙得以幸存，不过我得承认，真正有意思的都死光了。
This extinction event was not only distinctive for its speed, but the force of this blast is almost unimaginable.
这次灭绝事件不仅因为其发生速度而独特，而其摧毁力也几乎令人无法想象。
There are numerous kinds of extinction events.
历史上有过很多种灭绝事件。
Some can be local, where only a few plants and animal species are affected.
有些是本地的，只影响几种植物和动物种类。
Some can be regional, where quite a few species get it.
有些是区域性的，涉及的物种数量就比较多。
And then there are those events that are so enormous, they make modern Hollywood effects look like an Ed Wood movie effect.
还有那些极大的事件，它们使得现代好莱坞特效看起来像是艾德·伍德（1994年的电影）电影效果。
Scientists were initially at a loss to explain how this could have happened.
科学家们开始时无法解释这是如何发生的。
One theory pointed to global warming.
一种理论指向全球变暖。
Climate change had probably been a major factor in the first dinosaur extinction, so it seemed a likely candidate in the second one.
在第一次恐龙灭绝事件中气候变化可能是主要原因，所以它似乎是第二次的嫌疑对象。
The fact that the blast impacted on land and sea creatures alike, seemed to support this theory.
这次灾难对陆地生物和海洋生物的影响相似，这似乎支持这种理论。
Extinction is actually worldwide, it's not just a terrestrial phenomena, it doesn't occur just on land.
这次灭绝是全球性的，这不是陆地事件，它不仅发生在陆地上。
In fact most of the really spectacular extinctions have been based in the oceans.
其实很多非常惊人的物种灭绝都发生在海里。
So we have whole groups of animals which are simply not around today.
所以我们有很多类动物今天都无法见到了。
And extinction in the marine realm is really for the same reasons it occurs on land.
在海洋王国的灭绝其实和陆地上发生的原因一样。
In 1980, an unusually discovery would finally lift the veil of mystery.
在1980年，一个不寻常的发现最终揭开了谜团的面纱。
What Dr. Louis Alvarez, and his son, Dr. Walter Alvarez, uncovered set off a firestorm.
路易斯·阿尔弗雷兹博士和他儿子沃尔特·阿尔弗雷兹博士的发现，掀起了风暴。
In 1980, when Louis and Walter Alvarez were looking at the sedimentation rates, they weren't really interested so much in the extinction of dinosaurs,
在1980年路易斯和沃尔特·阿尔弗雷兹当时在研究沉积速度，他们对恐龙灭绝并没多大兴趣，
they were looking at, measuring the rate of sedimentation of deep ocean sediments.
他们关注的是，对深海沉积物沉积速率的测量。
One particular little layer though, however, showed a whopping increase in the concentration of the metal Iridium.
但其中有一小层却表现出金属铱的高度富集。
And they calculated if you were to spread the amount of Iridium in this layer that adds up to a total amount of material about equivalent to a ten-kilometer diameter asteroid.
他们计算过，要是把这一层里的铱的数量分散开来，那其材料总量就相当于一颗直径10千米的小行星。
A 10-kilometer asteroid, that's 6 miles wide - the size of Mount Everest.
直径10千米的小行星，那就是六英里宽，大小如同埃佛勒斯峰。
The reason why an asteroid was looked at as the cause of the Iridium spike at the K-T boundary, is because asteroids have an enormous amount of Iridium in them.
一颗小行星被看做是引起KT界限层铱猛增的原因，是因为小行星中有相当多的铱。
The earth has Iridium in it, but because it is a heavy metal, most of it settles towards the center of the planet.
地球也有铱，但因为它是重金属，多数都沉降到行星的中心。
But this thick layer of Iridium that separates the Cretaceous and Tertiary periods clearly was an anomaly and it had been deposited over a very short time.
但这个隔开了白垩纪和第三纪的厚铱层显然是个异常事物，而且它在很多的时间内便沉积下来。
But something else supported the asteroid theory.
还有其它证据支持小行星理论。
Along with the high levels of Iridium, they found something even more fascinating - shocked-quartz.
除了高度富集的铱以外，他们还发现了更为奇妙的东西——冲击石英
Shocked-quarts is a form of quartz that has a very different structure.
冲击石英是石英的一种形式，有很不一样的结构。
Under incredible pressure, the crystals within the quarts are deformed and actually fractured.
在极高压下，石英的内部结晶变现破裂。
Well, under magnification, you can see these deformations.
经过放大后就能看到这种变形。
There was only one other place where scientists had seen shocked-quartz - at the site of a nuclear bomb test that was conducted at the Alamogordon test range in New Mexico in 1945.
科学家们此前只在另外一处地方见过这种冲击石英 ，在一个核弹测试点，该核弹测试在1945年新墨西哥州的阿拉莫戈多试验场进行。
Shocked-quartz was first identified at the site of an underground nuclear bomb test.
冲击石英首次被确定是在一个地下核弹试验场。
It's that kind of force that causes this particular quartz to form,
正是那种巨大的力量导致了这种特殊石英的形成，
so finding shocked-quartz mixed within the high levels of Iridium was pretty darn clear evidence that something massive had hit the earth.
所以找到冲击石英加上高度富集的铱，就是相当确凿的证据，说明曾经有巨大物体撞击地球。