宇宙时空之旅（2014）

Cosmos: A SpaceTime Odyssey S01E07

Part 2 April 25, 2021, 12:40 p.m.

Fragments of the iron asteroid that made this crater
被完整地保留了下来
have survived intact.
如果我们知道那个铁块是什么时候形成的
If we just knew how long ago that iron was forged,
我们就可以知道太阳系的年龄
we'd know the age of the Solar System.
以及地球的年龄
Including the Earth.
可是我们怎么才能知道呢
But how could we know that?
选择一块岩石
Pick a rock.
任何一块岩石
Any rock.
这个怎么样
How about that one?
这块石头中有些原子有放射性
Some atoms in this rock could be radioactive,
也就是说这些原子会自发分解
which means they spontaneously disintegrate
变成其他元素
and become other elements.
一个铀原子先变成一个钍原子
A uranium atom first becomes a thorium atom.
一般来说至少需要几十亿年
On average, it takes a few billion years.
钍元素更不稳定
The thorium is much more unstable.
不到一个月它就会变成镤元素
In less than a month it turns into protactinium.
一分钟以后镤又变成了其他元素
A minute later, protactinium becomes something else.
原子经历十几次原子核变化
The atom undergoes ten more nuclear transmutations...
直到到达衰变链的最后一站
Until it reaches the last stop on the decay chain:
形成稳定的铅原子
A stable atom of lead.
铅原子会一直稳定地
And lead it will remain...
保持下去
For eternity.
20世纪人们几十年来付出了巨大的努力
In the 20th century there was a huge effort, lasting decades,
想要测量出每一种放射性元素变成另一种元素
to measure the time it takes for each radioactive element
究竟要多长时间
to transmute into another element.
物理学家发现每一种不稳定元素的原子
Physicists discovered that the atoms of each unstable element
都在以固定的速率衰变
decay at a constant rate.
原子核好像一处避难所
The nucleus of an atom is a kind of sanctuary,
环境的冲击和变化完全不能影响到它
immune to the shocks and upheavals of its environment.
用铁锤敲击
Hit it with a hammer.
放进油里煮沸
Boil it in oil.
使其汽化
Vaporize it.
原子钟依旧滴答作响
The nuclear clock goes on ticking,
严格执行着时间标准
keeping an absolute standard of time
丝毫不受太阳和其他恒星的影响
that does not look to the Sun and the stars.
除了铀原子还有什么更好的方案
What better way to find the true age of the Earth
测量地球的年龄吗
than with the uranium atom?
要是能搞清楚岩石中有多少铀原子
If you knew what fraction of the uranium in a rock
会衰变成铅原子
had turned into lead,
铀铅
你就可以计算出从岩石形成起
you could calculate how much time had passed
经过了多长时间
since the rock was formed.
可还有一个问题
But there's a problem.
地球最初形成的岩石
The rocks in the Earth that were present when it was formed
已经不存在了
are no more.
它们都经过了压碎融化再造的过程
They've all been crushed, melted, remade.
有一种方法可以测量出
There is a way to calculate the amount of lead
最初的铅含量
that was present from the beginning.
那就是来自太空的礼物
It's a gift from the heavens:
陨石
Meteorites.
撞击出陨石坑的陨石
This one... A fragment of the one
它的碎片就很理想
that made this giant crater... Was ideal.
这块陨石中的铅含量
The amount of lead deep inside this meteorite
与地球最初形成时的铅含量相同
is exactly the same as when Earth formed.
知道铀衰变的固定速率
Since you know the constant rate of uranium decay,
就能知道这块陨石的年龄
that should give you the age of the meteorite,
也就知道了地球的年龄
which was made at the same time as the Earth.
你需要做的
All you had to do was measure
就是测量出这块陨石内的铅含量
the amount of lead in meteorites.
很简单不是吗
Easy, right?
芝加哥大学一位名叫
A scientist named Harrison Brown,
哈里森·布朗的科学家
at the University of Chicago,
在1947年最先发现了这一点
first understood this in 1947.
他选中了一个年轻的研究生
He chose a young graduate student,
克莱尔·帕特森完成这项工作
Clair Patterson, to do the work.
帕特森当时并不知道这项工作
Patterson couldn't possibly know how this assignment
会改变他的一生
would alter the course of his life...
以及我们所有人
And ours.
这个看似纯粹的科学研究
What seemed like pure scientific research
得出的结果远超我们的想象
turned out to be so much more.
克莱尔·帕特森爱荷华州邮递员的儿子
Clair Patterson, son of a letter carrier from Iowa,
天生桀骜不驯在学校的成绩也不理想
was rebellious by nature and not very good in school.
但他是一位天生的科学家
But he was a natural born scientist.
一位名叫哈里森·布朗的地质学家
A geologist named Harrison Brown
给帕特森布置了一个看似简单的
gave Patterson what seemed like a straightforward
科学工作
scientific assignment.
首先帕特
First off, Pat...
我可以叫你帕特吗
You mind if I call you Pat?
我知道你不是地质学家
Now, I know you're no geologist...
也许你分辨不出花岗岩和长石
probably couldn't tell granite from feldspar...
可是我听说你对质谱仪很有研究帕特
but I hear you really know your way around a mass spectrometer, Pat.
很好你结婚了吗帕特
Good. You married, Pat?
是的劳里她也是一名化学家
Yeah, Laurie. Yeah, she-she's a chemist, too.
曼哈顿计划第二次世界大战期间美国陆军自1942年起开♥发♥核武器计划
我们一起在橡树岭参加
Uh, we worked on the Manhattan Project together,
曼哈顿计划
at Oak Ridge.
很好首先你要知道
Good. Okay, well, first thing you need to know:
这些小的晶体叫做锆石
There are these tiny crystals called zircons.
像针头一样小密度极高坚硬无比
Real small, size of a pinhead, tight as a drum and tough.
没有什么能穿过它
Nothing gets in or out of 'em.
我是说即使过了几十亿年
And I'm talking for billions of years.
我们之所以能知道这些颗粒的真实年龄
We know how old these grains are because we've already
正是因为我们测定了这些岩石的年龄
dated the rocks they came from.
每一块小小的锆石里只含有几百万分之一的铀
Each little zircon has only a few parts per million of uranium inside,
这些铀逐渐衰变成
and that uranium is decaying
含量更少的铅
to even tinier amounts of lead.
现在你已经知道如何测量铅含量
Now, you figure out how to measure that lead,
你以后会研究出如何测量陨石中的铅含量
and you'll know how to do it for a meteorite.
对吗帕特
You think you can do that, Pat?
是的为什么不能呢
Yeah. Yeah, I... I don't see why not.
很好因为你一旦成功了你就会成为
Good, because when you do, you'll be the first man
第一个揭开地球年龄之谜的人
to know the age of the Earth.
你会一举成名的
And you'll be famous.
你也知道
And you see,
这并不难
It'll be easy.
对你来说易如反掌
Duck soup.
锆石晶体
就在帕特森测量锆石颗粒中
While Patterson tried to measure
含有的微量铅元素的同时
the trace amounts of lead in the zircon grains,
另一名研究生乔治·蒂尔顿
another grad student, George Tilton,
测量出了同一颗粒中的铀含量
was measuring the amount of uranium in the same grains.
帕特森只需要
All Patterson had to do
用同样的精度测出铅含量就可以了
was measure the amount of lead with equal accuracy.
给你了帕特
She's all yours, Pat.
六次测量得出了相同的结论
Measured it six times. Same result:
百万分之三点二
3.2 parts per million.
干得漂亮乔治谢谢
Yeah, nice going, George, thanks.
蒂尔顿的实验得出了相同的结果
Tilton's results were always the same.
可帕特森对于同样颗粒铅含量的测量
But Patterson's results on the lead content of the same grains
结果却千差万别
were wildly inconsistent.
这讲不通
This made no sense.
难道是因为实验室
Could the lab have been contaminated
被之前进行过的铅实验污染了吗
by previous experiments with lead?
也许实验环境中自身含有
Maybe it was the naturally high amounts
极高的铅含量影响了他的实验结果
of lead in the environment that were messing up his results.
帕特森用尽了一切方法
Patterson did everything he could
除去实验室中的铅
to cleanse the lab of any lead.
几个月后
可最后测出的铅含量还是高出了100倍
There was still 100 times too much lead.
他已经耗费了两年多的时间
He had been at it for more than two years.
什么易如反掌全是骗人的鬼话
Duck soup, my ass.
超级净化
闲人免进
帕特森意识到他应该先把容器煮沸