生命的奇迹（2013）

证明彗星上的冰晶
that icy comets must have contributed
参与了地球海洋的形成
to the formation of our world's oceans.
刚形成的地球如同熔岩地狱
Earth began life as a molten hell.
它内部的热量蒸发了所有水分
Its internal heat drove off any trace of moisture.
但是不久之后 地球逐步冷却
But soon, the planet cooled
开始有云形成
and the first clouds grew.
然后 42亿年前
Then, 4.2 billion years ago,
一场似乎在太阳系所有行星上
a deluge, the like of which the solar system
都前所未有的暴雨倾盆而降
had never seen before or since, rained down.
再次感谢这些氢键
And again, thanks to those hydrogen bonds,
使水的沸点足够高
water's boiling point is high enough
让水一直存在于地表
to have allowed it to remain on the surface of the earth
直至今日
to the present day.
所以从很久很久以前
So from quite early in its history,
我们的地球家园就拥有了
our home has been able to hang on
这个至关重要的要素
to this most vital of ingredients.
不过要追寻另一要素的起源的话
But to trace the origin of the next ingredients,
你需要放眼地球之外
you have to look beyond our planet
来到离我们最近的恒星
To our nearest star.
和它发射的光线
And the rays of light it sends our way.
这是从洛斯莫奇斯开往奇瓦瓦州的火车
This is the train from Los Mochis to Chihuahua,
不知道为什么要在早上6点发车
which inexplicably leaves at 6:00am in the morning.
我所在这个地区在科特斯海海边
Um...the local name for this area in all the guidebooks
它在所有旅游指南上
is the Land of Turtles.
有个美丽浪漫的本地名字
Beautifully romantic name for this place
叫做海龟之地
on the Sea of Cortez.
但是我们刚刚发现
But actually we just found out
这个地方很有可能曾被叫做
that it's probably more likely to have been called
菠菜之地
the Land of Spinach-type Vegetables.
我们从菠菜之地来到"吉娃娃之地"
So we're going from the Land of Spinach-type Vegetables to Chihuahua,
奇瓦瓦州
which is the Land of Very Small Dogs.
这是世界上最棒的火车旅行之一
One of the great railway journeys of the world.
几乎所有生命都要依靠
Almost all life depends on the energy
太阳辐射的能量
that the sun sends our way.
但太阳并不是位仁慈的伙伴
But the sun is a far-from-benevolent companion
因为太阳辐射既养育了我们 同时也非常危险
because its radiant rain can be as dangerous as it is nourishing.
现在海拔大概与海平面持平
We're still round about sea level now
太阳刚刚出现在天边
and the sun is quite low in the sky.
现在七点左右 它很快就会升起来
It's about 7:00am, so it's not been up long.
我要用这个数字紫外线辐射计
And I'm going to measure the amount of UV radiation
测量一下每平方厘米
falling on every square centimetre with this,
受到多少的紫外线辐射
a digital, ultraviolet radiometer.
此时它显示 照到我身上的辐射
At the moment, it says there's about 22 microwatts
大约是22微瓦每平方厘米
per square centimetre falling on my skin.
而随着海拔上升
But as we climb in altitude,
紫外线需要穿越的大气层
then that UVB light is going to have to travel through
会越来越薄
less and less of the atmosphere,
被大气吸收的紫外线也越来越少
so less of it is going to be absorbed.
毫无疑问的是 当火车越行越远
And sure enough, as the miles pass by
进入内陆的群山深处
and we head into the mountainous interior,
辐射计的数值也开始变大
the meter readings start to go up.
现在大约是上午10点
Now it's about 10:00am,
太阳处于天空中较高的位置
so the sun's significantly higher in the sky.
火车也行驶到一定的海拔高度
The train's also climbed quite a bit in altitude.
此刻
Now...
紫外线辐射约为250微瓦每平方厘米
We're getting nearly 250 microwatts per square centimetre.
大约是之前测到的10倍以上
So that's about a factor of ten higher.
这是由于
And that's just because
从大气层顶到地面 紫外线需要穿过的大气
the UVB has had significantly less atmosphere to travel through,
变得越来越稀薄
from the top of the earth's atmosphere down to me.
这种辐射量在几分钟内晒伤裸♥露♥的皮肤
That's more than enough to burn unprotected skin
是绰绰有余了
in just a few minutes.
因为阳光里包含了太多
And that's because what arrived from the sun
我们看不见的物质
is far more than just the stuff we can see.
在光谱中 比可见光能量更高的辐射
Beyond the visible, the higher energy part of the spectrum,
有紫外线 特别是短波紫外线
there's ultraviolet light, particularly UVB,
能够穿透
which does get through
地球大气层 来到地表
the earth's atmosphere and gets to the surface.
短波紫外线可以惠及生命
Now, UVB can be beneficial to life.
比如人体利用它生成维他命D
We use it to produce vitamin D, for example.
但由于它具有较高能量
But because it's higher energy,
它也可能造成极大的危害
it can also be extremely damaging.
它可能破坏DNA
It can damage DNA,
它可能把皮肤晒得黝黑 以致晒伤
it can burn our skin as well as give us a suntan,
最终还可能引发皮肤癌
and, of course, ultimately, it can give us skin cancer.
既然地球上现存的生命
If ultraviolet light is a problem
都不能忽视紫外线带来的问题
for life on earth to deal with today,
物理学家便对生物学家
then the physicists might raise
提出了一个有趣的问题
an interesting problem for the biologists.
因为普遍观点认为 在35亿年前
Because we know that 3.5 billion years ago,
生命刚刚起源的时候
when life on earth began,
在可见光波段 那时太阳的亮度
although the sun was much dimmer
虽远不如现在
in the visible part of the spectrum,
但阳光中的紫外线却非常强
it was significantly brighter in the ultraviolet.
年轻的太阳就像一个矛盾体
The young sun seems like a paradox.
看起来不如现在明亮
It was fainter to the eye,
其亮度约是现在太阳的70%
perhaps 30% less bright than the sun we enjoy today,
但致命的紫外辐射却十分强烈
yet rich in deadly ultraviolet.
太阳的内核比现在旋转得快得多
Inside, the core was spinning much faster,
这使得电磁感应
which created more electromagnetic heating
更有效地加热了太阳表面
of the plasma on its surface.
等离子体又释放出更多能量
And this plasma emitted more energy,
不是频率较低的可见光
not in the lower visible frequencies,
而是高频的辐射
but in the higher frequencies.
比如X射线
Like X-rays...
以及紫外线
and ultraviolet.
似乎生命才刚刚在地球上安家的时候
It seems as if just as life was getting settled on its wet home,
年轻而昏暗的太阳 使其很难在地表存活
the faint young sun was making it tough to survive near the surface.
这里是墨西哥铜峡谷的顶点
This is the top of Copper Canyon,
也是火车之旅的终点
so the summit of the railway journey.
它高约2200米 也就是大约
It's about 2,200 metres, which is about...
在7000至8000英尺之间
what, somewhere between 7,000 and 8,000 feet.
现在测量一下紫外线辐射量
So I'll take a UV reading of the sun.
数值显示在260左右
It's actually reading about 260 now.
想想我们中午在海平面时测得的数值
Now, if you remember, at midday, down at sea level,
那时也显示在260左右
we were getting readings around 260.
虽然太阳的位置已经下降
So although the sun has dropped in the sky,
阳光以及紫外线需要穿过的大气层厚度增加
so the sunlight and the UV are coming through much more atmosphere,
但同时大气也变稀薄了
that's been compensated for by the thinness of the air up here.
因此这里的紫外线辐射量应该大于
I'm getting more UV now than I would have been
此刻我们能在海平面测到的辐射量
at the same time of day at sea level.
虽然我们不敢肯定
It's hard to be sure,
但我们认为早期生命所接受的辐射水平
but we think that it's these kinds of radiation levels
大概就在这样一个范围
that early life had to deal with.
因为那时太阳产生的紫外线辐射
Because back then, the sun's ultraviolet output
远高于现在的水平
was significantly stronger.
因此我们可以说
So I think it is fair to say
紫外线辐射可能对地球早期生命的发展
that that could have posed a significant threat
产生过很大的威胁
to the development of early life on earth.
如今 地球上的生命繁衍昌盛
Today, life has painted the surface of our home
并将世界装点得五彩斑斓
in all the colours of the rainbow.
不仅有红黄蓝绿
From greens to blues, reds to yellows,
还有橙色与紫色
oranges and violets.
而所有生命的色彩都源于
And the origin of all life's hues can be traced back
其与光线的相互作用
to the way it interacts with sunlight.
作为一名粒子物理学家 我考虑问题时
I'm a particle physicist, so I'm allowed to think of everything
都会着眼于粒子的相互作用
in terms of the interactions of particles.
我会将太阳光线想象成
So I would picture the light from the sun
一场粒子雨
as being really a rain of particles.
准确说是光子雨 各种能量等级的光子
Photons, they're called, particles of light of different energies,