与宇宙同龄的古老生命：英语精读讲义

Life has existed on one planet for about 4 billion years as far as we know, 短語搭配

据我们所知，生命在一颗星球上已经存在了大约40亿年，

but it might have started right after the Big Bang, 語法

但它可能在宇宙大爆炸之后就立刻开始了，

when the universe was much stranger and more fantastic than today.

那时的宇宙比今天更奇特、更不可思议。

A universe that might have allowed life to develop absolutely anywhere.

那样的宇宙或许允许生命在任何地方发展。

The cosmos might be full of the seeds of life, 習語

宇宙可能充满了生命的种子，

sleeping in a dead desert,

沉睡在死寂的沙漠中，

waiting for a few drops of rain to explosively bloom and grow.

等待着几滴雨水，便能爆炸般地绽放和生长。

Tiny and not so tiny aliens might be everywhere.

无论微小还是庞大的外星生物，可能无处不在。

In this video,

在这个视频中，

we're going to put together two highly speculative,

我们将结合两个高度推测性，

yet scientifically grounded possibilities. 短語搭配

但有科学依据的可能性。

Check out the scientific papers in our sources.

请查看我们来源中的科学论文。

To properly explain it,

为了恰当地解释它，

let's first look at the paradox of life on Earth.

让我们首先看看地球上生命的悖论。

The life paradox.

生命悖论。

For its first few hundred million years,

在它最初的数亿年里，

Earth was a magma hell,

地球是一个岩浆地狱，

constantly bombarded by asteroids.

不断遭到小行星的轰击。

But basically,

但基本上，

the second things calmed down and the first oceans formed, 語法

在一切平静下来、第一片海洋形成的那一刻，

life just appeared and zillions of microbes settled every nook and cranny they found. 習語

生命就出现了，无数的微生物占据了它们所能找到的每个角落。

This is kind of strange.

这有点奇怪。

Life on Earth seems to be almost as old as the planet itself, 語法

地球上的生命似乎几乎和这颗星球本身一样古老，

as if it was waiting around for an opportunity. 語法

就好像它一直在等待机会一样。

But life didn't only appear extremely quickly.

但生命不仅出现得极快。

In that tiny time window,

在那个极小的时间窗口内，

it also crossed a huge gap. 習語

它还跨越了一个巨大的鸿沟。

To qualify as living things, 短語搭配

要称得上是生物，

even microbes need to eat,

即使是微生物也需要进食、

poop,

排泄、

grow,

生长，

and multiply.

以及繁殖。

To do that,

要做到这些，

they need a genome,

它们需要基因组，

the biological instruction manual that sets the inner workings of an organism. 表達脈絡

也就是设定生物体内部运作机制的生物学指令手册。

How dead things with no genome became living things with genomes 語法

没有基因组的死物是如何变成有基因组的生物的，

is one of the biggest riddles of science.

这是科学界最大的谜团之一。

Simplifying a lot,

简单来说，

the problem is that to have a functioning genome,

问题在于，要想拥有一个运作正常的基因组，

you need proteins,

你需要蛋白质，

and to make those proteins,

而要制造这些蛋白质，

you need a functioning genome.

你需要一个运作正常的基因组。

Both proteins and genomes are super long molecules made of pretty complex blocks

蛋白质和基因组都是由相当复杂的模块组成的超长分子，

that are extremely difficult to assemble by chance.

纯靠偶然几乎不可能组装成功。

It's a chicken-egg paradox with several chickens and eggs. 習語

这是一个有着好几只鸡和好几个蛋的“鸡生蛋还是蛋生鸡”悖论。

Once you have a finished cell,

一旦你有了一个完整的细胞，

the whole system works efficiently.

整个系统就能高效运转。

But starting from simple dead stuff and reaching that level of sophistication by pure chance,

但是从简单的死物开始，纯粹依靠偶然达到那种复杂的程度，

should require an amazing amount of time for trial and error. 短語搭配

应该需要惊人的试错时间。

So,

那么，

how did the first living things manage to cross that gap

最早的生物是如何在短短的几亿年内，

in just a few hundred million years?

跨越那个鸿沟的呢？

Most theories about the origin of life try to explain that gap by theorizing how some primitive soup of prebiotic molecules 習語

关于生命起源的大多数理论，都试图通过推论前生源分子的原始汤，

could have efficiently produced the first self-replicating entities. 用詞

是如何高效地产生出第一个自我复制的实体，来解释这一鸿沟。

But we still don't know how exactly this would have worked.

但我们仍然不知道这一过程究竟是如何进行的。

Maybe we need to think backwards. 表達脈絡

也许我们需要逆向思考。

The clock of evolution.

进化之时钟。

Think of genomes as a book telling the history of life. 語法

把基因组看作是一本讲述生命历史的书。

As time passed and life evolved,

随着时间的推移和生命的进化，

more characters were introduced.

更多的角色被引入了进来。

Amoebae,

变形虫、

fish,

鱼类、

amphibians,

两栖动物、

dinosaurs,

恐龙，

and mammals.

以及哺乳动物。

Over billions of years,

经过了数十亿年，

the story of life got more and more complex. 語法

生命的故事变得越来越复杂。

A genome can be viewed as a long string of letters with biological instructions.

基因组可以被看作是一长串带有生物学指令的字母。

And from microbes to us today,

从微生物到今天的我们，

functional genomes seem to have been increasing in size at a fairly constant rate.

功能性基因组的大小似乎在以相当恒定的速率增加。

The functional genome of fish is more than twice that of worms. 語法

鱼类的功能性基因组是蠕虫的两倍多。

Our functional genome is about twice bigger than that of fish,

我们的功能性基因组大约是鱼类的两倍大，

and so on. 短語搭配

以此类推。

It is a bit more complicated,

实际情况要稍微复杂一点，

but for now,

但现在，

let's run with this. 習語

我们先以此为基础。

When we put all these clues together, 短語動詞

当我们把所有这些线索放在一起时，

it seems that genomes have been doubling in size on average every 350 million years or so. 短語搭配

基因组的规模似乎平均每3.5亿年左右翻一番。

As if evolution had been following an exponential inner clock.

就好像进化一直遵循着一个指数级的内在时钟。

But it gets even stranger.

但这变得更加奇怪了。

The very first microbes that emerged on Earth,

地球上出现的最早的微生物，

even if they look simple, 語法

即使它们看起来很简单，

already seem to have had pretty long and complex genomes.

似乎就已经拥有相当长且复杂的基因组了。

But how could life have achieved that level of complexity

但生命怎么可能在如此短的时间内，

in such a short time?

达到那样的复杂程度呢？

There may be an interesting way to solve this riddle.

或许有一个有趣的方法能解开这个谜题。

We just take our exponential clock and extrapolate it back in time to the simplest conceivable life form. 用詞

我们只需拿我们的指数时钟，将其向过去推算，一直推算到可以想象的最简单的生命形态。

Something equivalent to a being with a genome containing just a few letters.

相当于一个基因组里只有几个字母的生物。

But if we do that,

但如果我们这样做，

we end up 10 billion years in the past, 短語動詞

我们最终会回到100亿年前的过去，

more than twice the age of Earth,

这是地球年龄的两倍多，

which means,

这意味着，

if life actually evolved like this,

如果生命确实是这样进化的，

it didn't start here,

它就不会是在这里开始的，

but somewhere out there, 語氣意圖

而是在外面的某个地方，

in space.

在太空中。

This would explain why life started to thrive so quickly on our young planet.

这就解释了为什么生命在我们年轻的星球上如此迅速地繁衍开来。

If it was already present in space like a seed, 習語

如果它就像一颗种子一样早已存在于太空中，

it just needed water and warm temperatures

它所需要的只是水和温暖的温度，

to wake up and go on evolving. 短語動詞

就能苏醒并继续进化。

And it would also explain the high degree of sophistication

这同时也解释了地球上最早的生命形态，

of the first life forms on Earth.

为何具有高度的复杂性。

They could have been complex already because they might have been evolving for billions of years somewhere else in the universe.

它们可能已经很复杂了，因为它们可能已经在宇宙的某个角落进化了数十亿年。

But could life really be that old?

但是生命真的有那么古老吗？

Maybe,

也许，

yes.

是的。

Actually,

实际上，

life could have started shortly after the universe itself was born.

生命可能在宇宙本身诞生后不久就开始了。

A Goldilocks baby universe. 文化背景

恰到好处的婴儿期宇宙。

At its most basic level, 表達脈絡

在最基本的层面上，

life needs two things:

生命需要两样东西：

the right chemical elements to form complex molecules

用来形成复杂分子的合适化学元素，

and a liquid medium, 用詞

以及一种液体介质，

like water,

比如水，

in which those molecules can move and interact.

在其中，这些分子可以移动并相互作用。

The liquid medium needs to stay warm enough to remain,

液体介质需要保持足够的温度，以维持在

well,

呃，

liquid.

液态。

So,

因此，

when we search for life in space,

当我们在太空中寻找生命时，

we focus on Earth-like planets at just the right distance from their star, 短語搭配

我们会专注于距离恒星距离刚刚好、类似地球的行星，

warm enough to sustain liquid water.

温度要足以维持液态水。

But there was actually a time when almost all of the universe might have been habitable. 語法

但实际上曾经有一个时期，几乎整个宇宙都可能是宜居的。

Right after the Big Bang,

就在大爆炸之后不久，

the universe was extremely hot.

宇宙极度炽热。

But as the cosmos expanded,

但随着宇宙膨胀，

it cooled.

它冷却了下来。

And between about 10 and 17 million years after the Big Bang,

在宇宙大爆炸后约1000万到1700万年间，

when the universe was a thousand times younger than today,

当时宇宙比今天年轻一千倍，

it was between 100°C and 0°C,

它的温度在100°C到0°C之间，

the temperature at which water is liquid. 語法

正是水呈液态的温度。

So,

因此，

for this window of time,

在这个时间窗口，

more than 13.7 billion years ago,

即137亿多年前，

the whole universe absolutely every inch of it had the right temperature to support life. 習語

整个宇宙——绝对是每一寸地方——都拥有支持生命的适宜温度。

Of course,

当然，

the right temperature alone is not enough for life. 語法

仅有合适的温度对生命来说是不够的。

We also need chemical elements like carbon and oxygen,

我们还需要像碳和氧这样的化学元素，

which are forged in the cores of stars. 用詞

它们是在恒星的核心里锻造出来的。

But were there stars in super early cosmic times?

但是在极早期的宇宙时期有恒星吗？

Maybe,

也许，

yes.

有的。

In regions of the universe where matter was especially dense.

在宇宙中物质特别密集的区域。

Such stars would have been very massive and gone supernova in just 3 million years, 短語搭配

这样的恒星会非常巨大，并会在短短300万年内变成超新星，

seeding the baby universe with the chemical elements needed to form dust, 習語

为婴儿期的宇宙播下形成尘埃、

asteroids,

小行星、

planets,

行星、

and the ingredients of life.

以及生命成分所需的化学元素。

Maybe the first ancestors of life were more exotic and didn't even need water,

也许最早的生命祖先更奇异，甚至不需要水，

but thrived in substances like ammonia or ethane that can stay liquid at temperatures far below 0°C.

而是繁衍在氨或乙烷等在远低于0°C的温度下仍能保持液态的物质中。

They could have been sustained by the lingering warmth of the Big Bang for tens of millions of years longer, 用詞

它们可能依靠大爆炸残存的温暖继续存活了几千万年，

well into a time when we know for sure there were stars and all the chemical elements. 短語搭配

一直持续到我们确知有恒星和所有化学元素存在的时期。

The real magic of this idea is that while the universe today is extremely deadly and hostile, 表達脈絡

这个想法真正的神奇之处在于，虽然今天的宇宙极度致命且充满敌意，

back then,

但在那个时候，

the conditions for life might have been basically everywhere.

适合生命存在的条件可能无处不在。

For a period that may have lasted several dozen million years,

在那个可能持续了数千万年的时期里，

primordial life might have been able to emerge on any rock,

原始生命可能出现在任何一块岩石上，

even between the stars,

甚至是在星际之间，

sowing the universe with the seeds of what, 語法

在宇宙中播撒下生命的种子，

billions of years later,

数十亿年后，

would become bacteria,

它们会演变成细菌、

trilobites,

三叶虫、

dinosaurs,

恐龙，

and finally us.

最终成为我们。

At some point,

在某个时刻，

the universe cooled down below the right temperature for life to thrive, 短語動詞

宇宙的温度降到了适合生命繁衍的温度之下，

but some of those ancestral life forms may have continued to exist in the internal warmth of the first planets,

但那些古老的生命形态中，有些可能继续存在于早期行星内部的温暖之中，

frozen in asteroids,

冰冻在小行星里，

or hibernating in cosmic dust.

或者在宇宙尘埃中休眠。

Tiny seeds roaming the cosmos,

微小的种子在宇宙中游荡，

waiting for new hospitable places to continue evolving. 用詞

等待着新的宜居地以继续进化。

If they did,

如果它们确实如此，

life now might be everywhere in the universe.

那么现在的生命可能在宇宙中无处不在。

Will we ever know?

我们究竟会知道吗？

All this makes for a nice story, 短語動詞

所有这些听起来像是个不错的故事，

and while both the habitability of the baby universe and our exponential clock of life are reasonable ideas, 語法

虽然婴儿期宇宙的宜居性和我们的生命指数时钟都是合理的想法，

they're still speculative.

但它们仍然只是推测。

One more possibility among many others trying to explain our existence today. 表達脈絡

这是许多试图解释我们今天存在的可能性中的另一种。

But if life came to Earth from outer space, 語法

但如果生命是来自外太空才到了地球，

then it should have seeded other places in the solar system too.

那么它也应该在太阳系的其他地方播下了种子。

Maybe there are fossils in dry riverbeds on Mars.

也许火星干涸的河床里有化石。

Maybe we'll soon find life in the warm underground oceans of Enceladus or Europa. 文化背景

也许我们很快就会在土卫二或木卫二温暖的地下海洋中发现生命。

Titan has seas, 文化背景

土卫六拥有着由乙烷和甲烷构成的海洋、

rivers,

河流，

and lakes of ethane and methane as warm as the universe when it was 90 million years old.

和湖泊，其温度就和宇宙在9000万年时的温度一样温暖。

So,

所以，

finding exotic life on Titan would support the idea that life could have originated in the weird baby universe.

在土卫六上发现奇异生命将支持生命可能起源于奇异的婴儿期宇宙这一观点。

So far, 表達脈絡

到目前为止，

when we look out into the cosmos,

当我们望向宇宙深处，

we don't see anyone like us.

我们并没有看到任何像我们一样的存在。

But maybe that's because life needed 10 billion years or more to reach the level of complexity 語法

但也许那是因为生命需要100亿年或更长的时间才能达到那种复杂的程度，

that allows for a technological species.

从而允许技术物种的诞生。

Maybe there are millions of worlds filled with microbes, 表達脈絡

也许有数以百万计的世界里布满了微生物，

oceans full of exotic fish,

海洋里游满了奇异的鱼类，

and continents of bizarre animals.

大陆上遍布着奇异的动物。

And maybe even others like us that just recently gained consciousness

甚至可能还有其他像我们一样的生物，刚刚获得了意识，

and are beginning to look at the sky,

正开始仰望星空，

wondering if they're alone. 語法

想知道他们是否是孤独的。

Life could be flourishing right now in uncountable forms

生命此刻可能正在以无数种形式，

and in all kinds of cosmic environments.

在各种宇宙环境中繁衍生息。

And if many of us share a common cosmic origin, 語法

如果我们在很大程度上共享一个共同的宇宙起源，

we would all be part of a great cosmic family.

我们都将是一个庞大宇宙家族的一部分。

The answer may lie in our cosmic backyard. 習語

答案也许就在我们的宇宙后院里。

Let's go and find out.

让我们去寻找答案吧。