生命的奇迹（2013）

由两个氢原子和一个氧原子结合而成
two hydrogens and one oxygen atom bound together.
两个氢原子靠近一个氧原子
So two hydrogen atoms approach oxygen.
氧原子周围是由八个电子组成的电子云
Now, oxygen's got a cloud of eight electrons around it,
所以当氢原子靠近时
so when the hydrogens come in, then what happens is
氢原子的电子就被吸引过来 围绕着氧原子
the electrons get dragged over here, around the oxygen.
所以电子云的最终位置在这里
So you end up with an electron cloud around here,
而这里是孤立的带正电荷的质子
and, to some extent, pretty isolated, positively-charged protons out here.
所以这里是带正电的部分
So you get a net positive charge over here
而这里是带负电的电子云
and the electron cloud with its negative charge over here,
这就是一个极性分子
so you get what's called a polar molecule.
这就是为何你用一根带电的有机玻璃棒
And that's why, when you bring a charged Perspex rod
靠近水分子时 它们会向着玻璃棒弯曲
close to water molecules, they bend towards it.
水的极性意味着尽管水分子结构简单
Water's polar nature means that although its molecules are simple,
但它们可以形成奇妙且非常复杂的液体
together, they form a subtle, endlessly complex liquid.
并成为一种小生物的家园
A home in which one tiny creature thrives.
就是它 看
There he is. Look at that.
它 就是水黾
That...is a pond skater.
这种浮于水面的捕食者
A predator that floats on the surface of the water
可以利用水面感知猎物
and actually uses the surface of the water to sense its prey.
水黾是种凶猛的捕食者
Pond skaters are vicious predators
它们大半生都在水面度过
that live for most of their lives on the surface.
其腿部绒毛提供的大接触面♥积♥
Tiny hairs on their legs provide a large area
可以分散体重
that spreads their weight.
中足推动它们前进
Their middle legs thrust them forward.
后足控制方向
Hind legs are employed to steer.
它们非常适应这个平面世界
They're so well adapted to life in this flat world
甚至可以通过
that they even sense their sexual partners
水面微小的振动感知配偶
through tiny vibrations in the water's surface.
水黾有如此能力 是由于它对环境的适应
The reason it can do that is the result of a complex interaction
和水面物理化学特性
between adaptions in the animal itself
之间复杂相互作用的结果
and the physics and the chemistry of the surface of water.
水分子是极性分子
Water molecules are polar.
这意味着水分子可以互相结合
And that means that water molecules themselves can bond together.
当带有微弱正电荷的氢原子
So you can get a hydrogen with its slight positive charge
与其他水分子
getting close to the oxygen of another water molecule
带有微弱负电荷的氧原子靠近
with its slight negative charge
两者就会结合在一起
and bonding to it.
事实上 水分子
And you can build up quite large,
能大量地结合在一起
in fact, very large structures in liquid water.
水的独特特性
This is what gives water its unique ability
为水黾形成了一个平面栖息地
to form a surface habitat for the pond skaters.
一群群水分子聚在一起
Clumps of H2O stick together,
使水面具有张力
keeping the surface under tension.
水分子集在一处
Forming a chorus of water molecules,
靠氢键相互连结
all joined together by hydrogen bonds.
当水黾停落在水面上 它的腿部
Then a pond skater comes along and it puts its legs or its...
会接触水面并将其下压
dangly things into the water and pushes it down,
使水面弯曲
bends the surface of the water.
而水面会对抗这个弯曲
Now, the water doesn't like that
因为这会增加它的表面♥积♥
because a bend in the water is increasing its surface area.
还会增加其中的能量
It's increasing its energy.
这让水分子难以靠氢键结合在一起
It's making it harder for all the molecules to bond together
所以水往回推
with the hydrogen bonds. So they try to push back.
弯曲的水面给水黾腿部一定推力
They exert a force on the pond skater's leg
因为水分子要尽力地聚在一起
because they want to bond as much as they can.
这就是水黾能停在水面上的原因
And that's how pond skaters stay on the surface of the water.
氢键的作用
Hydrogen bonds do far more
不仅仅是给水黾提供了一个栖息地
than just give the pond skaters a place to live.
它是所有生命的根本
They're fundamental to all life.
我听说过一句话 要真正懂生物学
I've heard it said that we won't truly understand biology
就要先懂水
until we understand water.
这些是非常细小的玻璃管
These are...very thin tubes of glass.
它们的直径大约有一毫米
They're about what...a millimetre in diameter.
如果我将一支浸入水面
And if I dip one into the surface of this river...
看到水顺着管道往上爬了吗
Can you see that the water just climbs up the tube?
它对抗引力 将自己拉了上去
It pulls itself up, quite literally, against the force of gravity.
树木内部就有这些管道
Now, in trees, there are tubes
不过直径大约只有这支玻璃管的一半
which are about half the diameter of this,
约半毫米 甚至更细
perhaps about half a millimetre or even less.
它们被称为木质部
And they are called xylem.
木质部可以使水通过根系往上运送
And they allow the tree to lift water up through the root system
因为水分子能紧紧聚在一起
because the water molecules strongly attract each other
管道内侧也能吸附水分子
and are strongly attracted to the sides of the tubes.
所以当你看到参天大树 比如那一棵
So when you look at trees like that, which are very high,
你可以问自己一个问题
and you ask yourself the question,
"树木是如何将水从根部运送到顶部的"
"How do they get the water from the roots to the top of the tree?",
主要原因就是毛细作用
a big part of that is capillary action,
这要归结于水的极性特征
which is down to the polar nature of water.
水的一个重要特性
One of water's most important qualities
就是水可以溶解与携带
is its ability to dissolve and carry
生物所需的种种物质
all manner of substances around the living world.
因为水分子是非常小的极性分子
Because its molecules are very small and polar,
所以水是非常高效的溶剂
water is a tremendously effective solvent.
水分子可以挤进其他物质中
Those molecules can get in amongst other substances,
比如盐和糖 然后将它们溶解分散到
salts and sugars, for example, and disperse them, if you like,
氢键的海洋中
in that sea of hydrogen bonds.
在我们每个人体内
Within every one of us,
水在每个细胞间不断流动
water is constantly flowing around each and every cell.
血浆90%以上的成分是水
Blood plasma is over 90% water.
其中溶解了我生存所需的物质
And in it are dissolved everything I need to live -
氧 食物中的营养物质 所有东西
oxygen, the nutrients from food, everything -
通过人体内的水 送往全身各处
distributed around my body in rivers of water.
我们生活在这个美丽而不同寻常的蓝色世界
We live on a beautiful blue anomaly of a world.
地球是我们唯一已知被液态水覆盖的星球
The only planet we know with a surface drenched in liquid water.
水最初如何来到地球 这很难探寻
The story of how each drop ended up here has been hard to fathom.
主要因为年代实为久远
Largely because it happened so long ago,
没有直接的证据
there's very little direct evidence.
但是回到尤卡坦半岛丛林
But back in the Yucatan jungle,
我们仍可以找到水来源的线索
clues to how it turned up can still be found.
每一支生活在尤卡坦半岛的文明
Every civilisation on the Yucatan,
不管是玛雅人还是现今的墨西哥人
be it the modern Mexicans or the Mayans,
都得从深井 也就是溶井里获取水源
had to get their water from those deep wells, the cenotes.
我这儿有张完全等比例的地图
And I've got a map, a completely unbiased map
上边标注有较大的天然井的位置
of the larger cenotes here,
我将它覆盖在尤卡坦半岛的地图上
which I'm going to overlay on the Yucatan.
快看 它们呈正圆弧状
Look at that. They lie in a perfect arc,
围绕着一座特别的村落
centred around a very particular village,
就在这里 名字叫做希克苏鲁伯
which is...there, and it's called Chicxulub.
根据地质学家研究 只有极少数自然事件
Now, to a geologist, there are very few natural events
才能形成这种正圆弧形的构造
that can create a structure, such a perfect arc as that.
所有的证据指向一种解释
All the evidence points to just one explanation.
你所看到的是
You're looking at what's left
一枚巨大的小行星撞击地球的杰作
of a gigantic asteroid strike.
在6500万年前 它对地球的撞击
One that wiped out three-quarters of all plant and animal species
使地球上四分之三的动植物灭绝
when it hit the earth 65 million years ago.
也许你认为来自的太空碰撞只发生在过去
You may think that impacts from space are a thing of the past.
只发生在恐龙生活的年代
A thing that only happened to the dinosaurs,
这并不准确
but that's not true either.
每年有55000吨♥石块撞击地球
About 55 million kilograms of rock hits the earth every year.
其中含有大约2%的水
And around 2% of that is water.
这暗示地球上至少有部分水来自太空
This hints that at least some of earth's water arrived from space.
2010年末 哈雷二号♥彗星的照片
Late in 2010, these glimpses of comet Hartley 2
传回了地球
arrived back on earth.
这些照片由美国宇航局的
They were sent by
"深度撞击"彗星探测器发回
NASA's deep-impact probe.
彗星尘和冰晶从它表面飘进太空
From its surface, dust and ice spray into space.
通过对这些水的分♥析♥
Analysis of this water
发现其中的同位素组成
found it had a very similar mixture of isotopes
与地球海水的十分相似
to the water in our own oceans.
这是第一个确凿证据
This was the first firm evidence