了解宇宙是如何运行的（2010）

How the Universe Works S05E07

Part 4 April 18, 2021, 7:47 p.m.

39亿年前
3.9 billion years ago,
火星几乎倾斜了80度
Mars is tilting by as much as 80 degrees.
冬季气温降到华氏零下125度以下（零下87摄氏度）
Winter temperatures drop below minus 125 degrees fahrenheit.
随着极地冰盖迅速向赤道扩散
As the polar ice sheet spreads quickly toward the equator,
液态水和任何潜在的火星生命
liquid water is frozen solid,
都冻结成了固态
along with any potential martians.
驱动生命生化反应的水
The water that drives the biochemistry of life
会在微小细菌体内冻结
freezes inside the tiny bacteria.
冰晶的形成并刺穿火星生命的细胞壁
Ice crystals form and puncture the martian's cell walls
直到最终死亡
until eventually, they die.
每12万年，火星的倾斜度就会发生变化
Every 120,000 years the tilt of Mars changes,
因为星球的混乱摆动，使得火星生命
as again and again the planet's chaotic wobble
一次又一次地从深冻中抛进又抛出
flips the martians in and out of the deep freeze.
火星上的任何第二代生命……
Any second generation of life on Mars...
最终只剩一片狼藉
Is left in tatters.
与此同时，在地球上，我们的远古祖先却过得很轻松
Meanwhile, on earth, our ancient ancestors have it easy.
地球的摆动和季节保持相对稳定
The earth's wobble, and its seasons, stay relatively stable,
这都要归功于我们的秘密武器……
and it's all thanks to our secret weapon ...
我们的超大月亮
our oversized moon.
地球和月球的相互作用
The interaction of our planet and the moon
意味着我们的旋转轴非常非常稳定
means that the axis of our rotation is very, very stable.
季节变化一年又一年，一个世纪又一个世纪
The seasons return year after year, century after century,
几十亿年都是如此
for billions of years.
月球巨大的质量
Our moon's enormous mass
对地球产生了巨大的引力
exerts a huge gravitational pull on the earth,
稳定了地球的摆动
stabilizing the wobble of our planet
并控制了我们的气候
and keeping our climate in check.
如果没有月球
Without the moon, the early earth
早期的地球会像火星一样剧烈地摆动
would have wobbled just as wildly as Mars,
我们的祖先也会面临和早期火星生命一样的
and our ancestors could have faced the same icy fate
冰冻命运
as the early martians.
火星没有大卫星
Mars doesn't have a big moon,
只有两个很小很小的卫星
it has two, little, tiny moons
对它的影响很小
that don't really affect it much.
所以如果说火星的第一次生命
So if the martians were killed
是被巨大的撞击杀死的
the first time by a giant impact,
那么它的第二次很可能是
they may have been killed a second time
被火星本身杀死的，因为火星本身很不稳定
by Mars itself not being stable and flipping over
导致星球翻转了过来并出现了灾难性的超级冬天和超级夏天
and having catastrophic super winters and super summers,
基本上就是超级灾难性的气候变化
basically, mega catastrophic climate change.
在火星上，生命的前景
On Mars, the outlook for life
似乎很暗淡
seems bleak.
但将火星生命推向灭绝边缘的
But the brutal conditions that drive martian life
严酷环境也可能促使它们适应
to the edge of extinction may also have pushed it
并进化
to adapt and evolve.
我们之所以知道这一点，是因为在地球上
We know this because on earth organisms known as extremophiles
被称为极端微生物的有机体已经进化到可以生活在
have evolved to live in the most severe of circumstances,
最恶劣的环境中，从沸腾的、热液喷口……
from boiling, hydro-thermal vents...
到冰川的深冻，都有生命的痕迹
To the deep freeze of glacial ice.
当环境变得艰难时，生命似乎也变得更顽强
When the going gets tough, life seems to get tougher.
也许火星的超级冬天
Maybe the martian super winters
孕育出了第三代生命……
gave rise to a third generation of life ...
一支超级强悍的虫子大军是有可能
a super tough army of bugs able to survive
在最恶劣的气候变化中生存下来的
the harshest of climate swings.
我们在地球上看到的是
What we see on earth is that life evolves
生命进化到占据它所处的任何生态位
to occupy whatever niche it lives in,
然而这种进化需要时间
and that evolution takes time.
所以随着环境的改变，生命也随之改变
So as the environment changes, life changes with it.
如果有突然的变化
If there are sudden changes,
那么生命形式无法应对它，大多数都会死亡
then life forms can't cope with it and many die away.
而那些活下来的，就会继续演化
Those that survive, they continue on.
38亿年前
3.8 billion years ago
第三代生命可能已经在火星表面
a third generation of life could have thrived
繁衍生息
on the surface of Mars.
它们是由少数几种火星生命
Evolved from a handful of its predecessors
进化而来，熬过了火星上的超级冬天
to make it through Mars' super winters,
这是迄今为止火星上最艰难的生命
it's the toughest martian life yet.
但是，随着超级冬天的结束
But, as the super winters end,
火星生命面临的挑战将变得更加糟糕
the challenges for life on Mars are set to get worse.
另一个灭绝级别的事件即将发生
Another extinction-level event is on the way.
火星的大气层正在被一个分子一个分子地撕裂
Mars' atmosphere is being ripped away molecule by molecule.
“这一拳”是否就是
Could this be the killer punch
彻底消灭火星生命的那致命一击呢？
that wipes out the martians for good?
想象一下
Imagine Mars
38亿年前的火星
3.8 billion years ago.
这是一个温暖潮湿的世界
It's a warm, wet world,
超级顽强的细菌在蓬勃发展
and super tough bacterial life is thriving.
但这些火星生命并不是火星上的第一批居民
But these martians are not the planet's first inhabitants.
第一代火星命在巨大的
The first generation of martian is vaporized
北极撞击事件中蒸发了
by the huge borealis impact.
也许生命已经从头开始
Perhaps life starts over from scratch,
但经历了一系列极端的气候变化
but endures a series of extreme climate swings.
只有最坚强的火星生命才能熬过去
Only the toughest martians make it through.
但另一场灾难即将来临
But another disaster is about to strike,
这场灾难将考验最强壮的火星生命
and this catastrophe will test even the strongest martians.
他们即将失去生命中最基本的组成部分…
They're about to lose the most basic ingredient of life ...
液态水
liquid water.
你必须意识到在行星表面
You really have to appreciate how difficult it is
有液态水是多么的困难
to have liquid water on the surface of a planet.
我们知道，当周围有液态水时
We know that life works so well
生命就会运行得很好
when there's liquid water around.
但如果要保持液态水
But you need just the right balance
就需要气压和温度的平衡
of air pressure and temperature.
如果没有了
Without air pressure
大气的压力
weighing down on it,
那么无论温度如何，液态水都会
liquid water will evaporate from the surface of a planet,
从行星表面蒸发
whatever the temperature.
这种气压是由于
That air pressure is generated
大气的存在而产生的
by the presence of an atmosphere.
在很多方面
In a lot of ways that atmosphere
大气就像一个盖子
serves as a kind of a lid
阻止水进入太空
stopping down the water from escaping into space.
这种大气压非常重要
It's very important to have that atmosphere.
37亿年前
3.7 billion years ago,
地球上的生命享受着温暖的海洋和厚重的大气层
life on earth enjoys warm oceans and a thick atmosphere.
但在火星上，第三次灭绝级别的事件
But on Mars, a third extinction-level event
正蓄势以待
is gaining momentum.
大气层正在慢慢被剥离
The atmosphere is slowly being stripped away,
火星上的海洋开始蒸发
and Mars' great oceans are starting to evaporate.
这两个行星上的生命
The fate of life on both planets
现在他们的命运都取决于星球磁芯的强度
now rests on the strength of their magnetic cores.
事实证明，地球上大气层的存在
It turns out that the existence
可能依赖于地球的磁场
of an atmosphere on earth may rely on the magnetic field,
因为我们磁场的作用
because what our magnetic field does
就是保护我们免受一种风的冲击
is it protects us from the onslaught of this wind,
一种来自于太阳的
of subatomic particles
持续吹出的亚原子粒子流
that the sun is blowing out all the time.
我们把它称之为太阳风
We call this the solar wind.
如果我们没有这样一个磁场
And if we didn't have a magnetic field
捕捉这些粒子并使其轻微偏转
to basically catch and deflect those particles gently,
那么它们就会直接撞击地球大气层
they would directly slam into the earth's atmosphere.
如果你把磁场看作
If you think of the magnetic field
抵御太阳风的风衣
as a windbreaker from the solar winds,
一旦我们失去了这种保护
once we lose that protection,
地球就会变得非常脆弱
that planet becomes very vulnerable.
地球的地核
The earth's magnetic core
在34.5亿年的时间里一直保持强壮
has stayed strong for 3.45 billion years
超级热的铁水像熔岩灯一样
as super hot molten iron churns over and over
在地球内部不断翻腾
within the planet like a lava lamp.
翻腾的铁产生了电
Churning iron creates electricity,