行星（2019）

of standing water on Mars around 4 billion years ago,
当时的大气压力与地球目前情况相当
and the atmospheric pressure was at least that of Earth today,
甚至更高
perhaps even higher.
气温约为25摄氏度 在那个时候我也许完全可以
Temperatures were around 25 degrees, so I could have sat on Mars
坐到火星上 可能需要戴个呼吸面罩
all those years ago, admittedly with a mask to breathe,
因为那里的氧气很稀薄 但我可以坐在那里
because there was very little oxygen, but I could have sat there
欣赏到这样的风景
and looked out over a view like that.
所以我们不必只去想象火星曾经的样子
So, you don't have to imagine what Mars was like in the past.
我们可以真切地体验到
You can experience it.
就像现在这样
It was pretty much like this.
但在后来的10亿年间
But, within a billion years,
火星上的湖泊和海洋全部消失了
all Mars' lakes and seas had disappeared.
太阳系中 只剩下唯一一颗蓝色的星球
In our solar system, only one blue planet survives...
那就是火星的姐妹行星 地球
..Mars' sister, Earth.
地球表面的70%被海洋覆盖
70% of our planet's surface is covered by ocean.
成百万的物种在海洋中繁衍生息
Under the waves, a million species thrive.
在陆地上 雨水维系着地球微妙的生态系统
While on land, the rains support Earth's delicate ecosystems...
为大量的生命提供家园和庇护
..providing a home for an abundance of life.
但它并非一直如此
But it hasn't always been this way.
地球 40亿年前
早期的地球与我们今天所知的地球不同
The early Earth was unrecognisable from the planet we know today.
早期地球大气中的二氧化碳浓度很高
Its atmosphere thick with carbon dioxide.
地球上的海水呈酸性
And its oceans acidic.
40亿年前 地球曾是一个有毒的混乱世界
Four billions years ago, Earth was a troubled, toxic world...
而当时的火星正在蓬勃发展
..while Mars was flourishing.
但两颗行星都将被太空的
But both planets were about to be engulfed
一场大灾难吞没
by a cataclysm from space.
为了了解当时的情形
To understand what happened,
我们必须将眼光投向地球以外的地方
we have to look beyond our own world.
仅观察地球表面 是无法去解读
You can't read the deep history of the Earth by looking
其久远历史的 因为地球的地质活动频繁
at its surface because our planet is a geologically active world.
由于火山活动 风化作用和海洋的作用
The surface is constantly being reshaped by volcanic activity,
地球表面不断地发生变化 但我们有一位同伴
weathering, and the actions of the oceans, but we have a companion,
那就是月球 数十亿年来 月球一直不活跃
the moon, which has been inactive for many billions of years,
因此太阳系在这个区域发生的一切
and so the history of events that happened in this region
都被记录在了月球的表面
of the solar system is written all over its surface.
遍布陨石坑是月球表面最显著的特点
The most distinctive feature of the moon's surface
月球表面记录下了所有来自太空的撞击
are its craters - it is literally covered in a record of impacts
我们可以据此分♥析♥月球不同部分的
from space, and that allows us to estimate the relative ages
相对年代
of different parts of the moon.
很简单
Quite simply, if there are more craters,
陨石坑更多的区域一定更古老
then that piece of the moon must be older.
这说明它被撞击的次数更多
There's been more time for the impacts to build up.
但除了判断相对年代 我们还可以做得更多
But we can do better than just measure the relative ages
因为我们还有岩石 阿波罗号♥宇航员
because we have rocks, the moon rocks brought back
带回来的月球岩石
by the Apollo astronauts.
我们可以分♥析♥岩石内部放射性元素的衰变速度
We can estimate the ages of rocks very precisely by looking
非常准确地判断岩石的年龄
at the rates of decay of radioactive elements inside them.
它们就像小小的秒表 从岩石形成的那一刻
They're like little stopwatches that start ticking the moment
开始滴答作响 这些都是太空撞击带来的
the rocks are formed, in this case by the impacts from space.
因此我们可以将某个月球区域的
So, the moon rocks allow us to tie the number of craters
陨石坑数量
in a particular region of the moon
和岩石的绝对年龄联♥系♥起来分♥析♥
to an absolute age measured by the rocks.
这不仅能帮助我们确定月球表面受到撞击的时间
And this doesn't just allow us to date impacts on the lunar surface.
毛德陨石坑
哈德利陨石坑
我们还能通过陨石坑
It means that craters can be used
分♥析♥太阳系的演化历史
to read the histories of worlds across the solar system.
涅库姆陨石坑
也包括火星的历史
Including Mars.
当我们将所有数据集中在一起 我们有了惊人的发现
When we gathered all the data, we discovered something surprising.
约38亿到39亿年前 陨石坑形成的速度
There was a peak in the crater formation rate, about 3.8
达到峰值
to 3.9 billion years ago,
这表明整个太阳系内在这个时期出现了剧烈的天体撞击
which signified a period of intense violence in the solar system,
这被称为晚期重大撞击事件
and that is called the Late Heavy Bombardment.
火星 39亿年前
无数小行星冲进火星的大气层燃烧解体
Countless asteroids fragmented in Mars' atmosphere,
给整个火星带来了一场浩劫
raining havoc across the planet.
据估计 在火星表面
It's estimated that 53 tonnes of rock
每平方米有53吨♥岩石落下
fell on every square metre of Mars.
超过三分之一的火星表面伤痕累累
Over a third of the planet's surface was obliterated...
火星被推到了死亡的边缘
..and Mars was pushed to the brink of death.
月球表面的证据告诉我们太空曾发生
Whilst the evidence from the surface of the moon tells us
晚期重大撞击事件 但并未揭示其中的原因
that the Late Heavy Bombardment happened, it doesn't tell us why.
为此 我们需要通过计算机模型
For that, we have to resort to computer models of the evolution
来还原太阳系的演化过程 在研究中
of the solar system, and, when we do that,
我们发现根源来自海王星
they point the finger at Neptune.
人们认为海王星在向外迁移时经过了柯伊伯带
It's thought that Neptune migrated outwards into the Kuiper belt...
无数冰质岩石天体集中在这里
..a region of icy, rocky objects
运行于太阳系的边缘地区
orbiting at the edge of the solar system.
天体间由此产生的相互引力破坏了这些轨道
The resulting gravitational interactions disrupted those orbits
并将很多天体推向太阳系的内部
and sent many of the objects inwards to the inner solar system,
这很可能导致了晚期重大撞击事件的发生
and that may have been the cause of the Late Heavy Bombardment.
地球 39亿年前
地球当时也遭受了猛烈的撞击
Earth also suffered the onslaught,
在此后的数千万年里
and, for tens of millions of years,
这两颗姐妹行星的命运一直悬而未决
the fortunes of the two sister worlds hung in the balance.
但就在这种最不乐观的条件下
But, just when conditions appeared at their least promising,
地球最重要的特征出现了
Earth's most precious characteristic emerged.
生命
Life.
有充足的证据表明 约38亿年前
There is good evidence that life was present on Earth
地球就已出现生命 我认为可以排除
around 3.8 billion years ago, and discounting the - I think -
那种最小的可能性 就是生命起源于
remote possibility that life began elsewhere
太阳系的其它地方 又被陨石或彗星
in the solar system and was transported to the Earth
带到地球的说法
on meteorites or comets,
那么可以说生命一定是从地球开始的
that means that life must have begun here.
在这颗行星的某个地方产生了
So, somewhere on this planet there was a transition
由地球自身的化学变化
from geochemistry - the chemistry of Earth,
转变为了生物化学的演变
to biochemistry - the chemistry of life.
但这样的转变到底是如何产生的
And whilst the precise details of how that transition occurred
至今仍是个迷 人们认为温暖的火山池
remain a mystery, it's thought that in warm volcanic pools
或深海热泉口最适宜构成
or deep sea hydrothermal vents, conditions were right
生命的基本化学单位自发形成
for the chemical building blocks of life to form spontaneously.
这意味着 如果太阳系的其它地方
And that means that if similar conditions
也存在相似的条件
were to be found elsewhere in the solar system,
就也有可能诞生生命
it might be possible that life began there too.
阿特拉斯-5运载火箭点火升空
Ignition, and lift off of the Atlas V rocket with MRO.
火星勘测轨道飞行器
火星勘测轨道飞行器发射成功
Surveying for the deepest insights
开始深入探索火星的神秘演变
into the mysterious evolution of Mars.
2005年 美国国家航♥空♥航♥天♥局开始了
So, in 2005, NASA embarked on a mission to look
在火星寻找相同环境的任务
for those same environments on Mars.
火星 现在
10多年来 火星勘测轨道飞行器
For more than a decade, the Mars Reconnaissance Orbiter
一直在关注这颗红色星球
has been our eyes on the Red Planet...
美国国家航♥空♥航♥天♥局 火星勘测轨道飞行器
它传回的数据
..sending back more data
它传回的数据远多于其它火星任务传回的数据之和
than all the other Mars missions combined.
火星勘测轨道飞行器拍摄了6万多张图片
MRO has made more than 60,000 orbits,
覆盖了99%以上的火星表面
mapping over 99% of the planet's surface.
它的高分辨率摄像机揭示了一个前所未有的火星
Its high-resolution cameras have revealed Mars as never before,
人们发现了极地雪崩
discovering polar avalanches,
以及流动的沙丘
shifting sand dunes...
还有沙漠 甚至液态雪融水的季节性流动
..and what could be seasonal flows of sand or even liquid meltwater.
2017年 火星勘测轨道飞行器开始关注
Then, in 2017, MRO turned its gaze
红色星球最古老的特征之一
to one of the Red Planet's oldest features,
波江盆地
the Eridania Basin.
波江盆地 38亿年前
38亿年前 这个盆地还是一片汪♥洋♥
3.8 billion years ago, the basin was a vast sea...
这里的水容量
..holding ten times more water
是北美五大湖区水容量的10倍
than the Great Lakes of North America.
火星勘测轨道飞行器在这里发现了找寻已久的证据
And it was here that MRO found the evidence it was looking for.
400米厚的矿物沉积 这通常形成于
400-metre-thick deposits of minerals that, on Earth,
地球的深海热泉口
form in deep sea hydrothermal vents.
在波江盆地 火星勘测轨道飞行器发现
In the Eridania Basin, MRO revealed that conditions on Mars
火星出现过适合孕育生命的条件