宇宙时空之旅（2014）

Cosmos: A SpaceTime Odyssey S01E11

Part 2 April 25, 2021, 12:41 p.m.

There were smaller amounts of nitrogen,
氩气水蒸气和氧气
argon, water vapor and oxygen.
几年后
A few years later,
当科学家开始分♥析♥
when scientists thought to analyze the gasses
那喀拉陨石
那喀拉陨石内部的气体
trapped inside the Nakhla meteorite,
和类似陨石的气体组成时
and other members of its class,
火星大气
他们发现了惊人的相似性
they found a striking similarity--
绝大多数陨石
the vast majority of meteorites
都是其他行星的碎片
are fragments of asteroids.
但坠落在那喀拉的陨石
But the kind that hit Nakhla, on Earth,
却只能来自一个星球
could only have come from one place...
火星
Mars.
欢迎来到火星
Welcome to Mars.
十亿多年前这里的一处火山爆发
Over a billion years ago, a volcano erupted here
熔岩冷却后形成了坚硬的岩石
and its lava cooled into solid rock.
数亿年过后
Hundreds of millions of years later,
这片区域被洪水冲刷
this area was flooded with water.
洪水过后很久
And long after that flood,
一块直布罗陀巨岩般大小的小行星
an asteroid the size of the Rock of Gibraltar
撞到了火星表面
crashed into the Martian surface,
炸出来一个巨大的火山坑
blasting out a huge crater.
很多碎片被抛回太空
Much of the debris was ejected back out into space,
围绕太阳旋转
where it orbited the Sun until
直到来自母星球火星的引力扰动
a gravitational tug from its home planet, Mars,
将其中的一块巨岩
diverted one of the boulders
偏转到能和地球碰撞的轨道
into a collision course with Earth.
它的到来令小小的那喀拉为之震惊
Its arrival shook up the little village of Nakhla.
如果把太阳系比作一个交通系统
Meteorites of the type that hit Nakhla
那撞击那喀拉的陨石就好比系统里的交通工具
are the vehicles of a natural interplanetary transit system
在各个行星之间运送岩石
that sends rocks between the planets.
这样的陨石好似一艘微生物的救生船
Such a meteorite can safely shelter microscopic cargo--
承载了生命的种子
the seeds of life--
如同一艘行星际方舟
an interplanetary ark.
许多岩石是多孔的带有很多藏身之所
Most rocks are porous, full of tiny nooks and crannies,
让生命有搭便车的机会
where life can stow away.
我们知道一些细菌可以在
We know that some microbes can survive
恶劣的宇宙环境下存活
the hostile environment of space.
以这些细菌为例
Take these guys, for instance.
它们在国际空间站的外表面
These microbes spent a year and a half
生活了一年半之久
riding on the outside of the International Space Station,
暴露在宇宙的极端温度真空
exposed to the extreme temperatures, vacuum,
以及太空辐射之中
and radiation of space.
当它们被带回地球时
And some of them were still alive and kicking
其中一些依旧生命力旺盛
when they were brought back to Earth.
更令人惊讶的是这些细菌
Even more astonishing are these creatures,
竟然在八百万年死寂般的沉睡后苏醒
awakened from a deathlike sleep of eight million years.
它们在南极大♥陆♥冰封了数百万年
They were frozen in the Antarctic ice millions of years
那时我们人类还不存在
before our species even existed.
而它们却仍然活着
And they're still alive.
如果生命可以抵御宇宙的严酷
If life can withstand the hardships of space
忍♥耐数百万年
and endure for millennia,
那它一定可以搭乘天然的星际旅行系统
then it could ride the natural interplanetary transit system
在各个行星间穿梭
from world to world.
可以大胆猜测我们的微生物祖先
It's a good bet that our microbial ancestors
在宇宙中漂流了很久
spent some time in space.
为什么这么说呢
Why do we think so?
地球的年龄是四十五亿年
The Earth is four-and-a-half- billion-years old.
在它的前半生里
For the first half of its lifetime,
巨大的小行星每隔几百万年
large asteroids were bombarding the planet
就要光临一次
every few million years.
最为强烈的几次撞击将海洋汽化
The most violent impacts vaporized the oceans
甚至融化了地表的岩石
and even melted the surface rock.
每次这样的撞击
Each such collision
都会让地球上的细菌
would have completely sterilized the planet
灭绝几千年
for thousands of years.
但我们通过分♥析♥化石得知
But we know from fossils in the rocks
在地球的形成期内
that bacteria were evolving on Earth
细菌也在进行着进化
during this formative period.
那它们是如何在这样的条件下得以存活呢
So how could life have survived such a lethal series of blows?
只要当体积较大的小行星撞击地球时
Whenever one of those big asteroids hit the Earth,
爆♥炸♥都会形成一个陨石坑
the explosion would blast out a crater,
同时将数百万块碎片发射回宇宙
launching millions of boulders into space.
许多碎片的内部都携带了细菌
Many of those rocks carried living bacteria inside.
其中的一些在宇宙中存活下来
Some of the bugs would have survived in space,
留在地球上的细菌因高温灭绝
while all those left behind on Earth would have been fried.
每次撞击后的数百年
A few thousand years after each impact,
地球将逐渐冷却
the Earth would have cooled down enough
直到足以将水蒸气凝结成海洋
for water to condense into oceans.
整个地球将重新可供居住
The planet would again be habitable.
同时那些被发射到宇宙中的碎片
Meanwhile, most of the rocks launched into space
将围绕太阳旋转
would have been orbiting the Sun.
其中一些将重新和地球相遇
Some of them would encounter the Earth again,
穿过大气成为陨石
reenter the atmosphere as meteorites,
把珍贵的细菌带回地球
and deliver their precious cargo of life
再次生根发芽
to re-seed the planet...
好比诺亚方舟
like Noah's ark.
这将意味着生命的进化
What this means is that life doesn't have to
不必在每次灾难后推倒重来
start over again from scratch after each catastrophe.
它可以哪里跌倒哪里爬起来
It can pick up where it left off.
当太阳系还很年轻时
When the solar system was young,
金星和地球十分相似
Venus was probably more like Earth,
拥有大海甚至生命
with oceans and maybe even life.
金星地球和火星通过小行星的撞击
Venus, Earth, and Mars were all exchanging rocks
彼此交换岩石碎片
with each other, due to asteroid impacts.
地球上的生命会携带
Does life on Earth carry any traces
远古时期星际旅行时留下的痕迹吗
of interplanetary voyages made in the distant past?
为什么有些细菌可以在
Why is it that some microbes can survive
辐射强烈和真空的宇宙环境下存活
the intense radiation and vacuum of space?
地球上没有这些条件
These conditions don't naturally exist on Earth.
也许这些细菌正在告知我们
Maybe those bugs are telling us
它们的祖先在几十亿年前的宇宙中经历了
that their ancestors survived those same conditions in space,
同样的环境
a few billion years ago.
现在我们知道了细菌可以隐蔽在岩石中
So we know that microbes can stow away in rocks
在行星际旅行中存活下来
and survive the voyage from planet to planet.
那么它们在恒星之间的旅行又是怎样的呢
But what about trip from star to star--
会是一场恒星际冒险之旅么
an interstellar odyssey?
这是蒲公英
The dandelion.
大约三千万年前
Around 30 million years ago,
它进化出另外一种方式
it evolved another way to send its own message of life
在时空中传递生命的信息
through space and time.
它的每粒种子都像一个伞兵
Each seedling is a little paratrooper,
随风飘荡
floating on the wind,
踏上冒险之旅只为寻找安全的着陆地点
risking everything for a safe place to land.
上升气流可以把它们带向空中
Updrafts can carry them higher into the air.
一只蒲公英可以飞行几十
A dandelion can travel dozens,
乃至数百千米的距离
possibly hundreds of kilometers,
甚至可以飞越山脉
even crossing over mountain ranges.
进化使蒲公英变成一只精巧的飞行器
Evolution has shaped it into an exquisite flying machine.
它的种子也算是一种方舟
The seed is another kind or ark,
通过驾驭流动的空气
ensuring the survival of its species
从而来到安全的地方得以存活
by riding the currents of the atmosphere to safe harbors.
每粒种子的DNA都带着一个故事
Each seed in its DNA carries a story,
讲述了下一个蒲公英的特征和命运
the character and destiny of the next dandelion--
生命就在这样的故事中代代相传
life propagates by retelling its story.
生命能够在恒星之间的旅行中
Is it possible that life could survive the journey
幸存下来吗
from star to star?
恒星之间的距离一百万倍于
The stars are about a million times farther apart from each other
行星之间的距离
than are the planets.
宇宙如此浩瀚
Space is so vast
以至于一颗地球上抛射出去岩石