This ancient rock is changing our theory on the origin of life | Tara Djokic

翻译人员: Yan Gao 校对人员: Yolanda Zhang

The Earth is 4.6 billion years old,

地球的寿命有46亿年，

but a human lifetime often lasts for less than 100 years.

但人类的寿命还不到100年。

So why care about the history of our planet

那我们为什么要关心地球历史呢，

when the distant past seems so inconsequential to everyday life?

它那么遥远，好像 与我们的生活完全无关。

You see, as far as we can tell,

就我们所知，

Earth is the only planet in our solar system

在太阳系里，只有地球

known to have sparked life,

拥有灿烂的生命，

and the only system able to provide life support for human beings.

也只有地球能提供 让人类存活的环境。

So why Earth?

为什么偏偏是地球？

We know Earth is unique for having plate tectonics,

我们知道地球是独一无二的， 它有板块构造、

liquid water on its surface

表面有液体水、

and an oxygen-rich atmosphere.

还有富含氧气的大气层。

But this has not always been the case,

但并不是一直这样，

and we know this because ancient rocks have recorded the pivotal moments

因为古岩石记录了地球演化过程中

in Earth's planetary evolution.

的每个关键时刻。

And one of the best places to observe those ancient rocks

观察古岩石的最佳去处之一，

is in the Pilbara of Western Australia.

是澳大利亚西部的皮尔布拉。

The rocks here are 3.5 billion years old,

这里的岩石存在了 35 亿年之久，

其中藏着地球上 最早期生命的证据。

and they contain some of the oldest evidence for life on the planet.

Now, often when we think of early life,

通常，说起古生命时，

we might imagine a stegosaurus

我们想到的是剑龙，

or maybe a fish crawling onto land.

或者一种鱼爬到了陆地上。

But the early life that I'm talking about

但我说的古生命，

is simple microscopic life, like bacteria.

是简单微生物，比如细菌。

And their fossils are often preserved as layered rock structures,

它们的化石通常是层叠的岩石结构，

called stromatolites.

称为叠层石。

This simple form of life is almost all we see in the fossil record

地球出现生命的前 30 亿年里，

for the first three billion years of life on Earth.

化石记录中几乎只能见到 这种简单的生命形式。

Our species can only be traced back in the fossil record

在化石记录中寻找人类的踪迹，

to a few hundred thousand years ago.

只能追踪到几万年前。

We know from the fossil record,

从化石记录中我们了解到，

bacteria life had grabbed a strong foothold

细菌生命开始得很早，

by about 3.5 to four billion years ago.

大约 35 至 40 亿年前就存在了。

The rocks older than this have been either destroyed

而比这个时间更久的岩石，

or highly deformed through plate tectonics.

要么被破坏了， 要么随板块运动过度变形。

So what remains a missing piece of the puzzle

所以遗留下来一个 待解决的难题就是，

地球上的生命到底是 什么时间开始的。

is exactly when and how life on Earth began.

Here again is that ancient volcanic landscape in the Pilbara.

回到皮尔布拉的古火山地貌。

Little did I know that our research here would provide another clue

我当时完全不知道，我们在这里 的研究会给生命起源之谜

to that origin-of-life puzzle.

提供另一个线索。

It was on my first field trip here,

那是我第一次到这里实地考察，

在整整一周的地图绘制项目 快要结束时，

toward the end of a full, long week mapping project,

that I came across something rather special.

我发现了一件不寻常的东西。

Now, what probably looks like a bunch of wrinkly old rocks

这一堆纹路横生的石头，

are actually stromatolites.

其实是叠层石。

And at the center of this mound was a small, peculiar rock

在这一堆的中间，是一块 小小的罕见的岩石，

about the size of a child's hand.

像小孩的手那么大。

It took six months before we inspected this rock under a microscope,

我们花了六个月才得以 在显微镜下观察它，

when one of my mentors at the time, Malcolm Walter,

当时我的一位老师， 马尔科姆·沃尔特，

suggested the rock resembled geyserite.

提出这石头像硅华。

Geyserite is a rock type that only forms

硅华是一种岩石类型，它的形成地

in and around the edges of hot spring pools.

只在热泉池里面和边缘周围。

Now, in order for you to understand the significance of geyserite,

为了让各位理解硅华的重要，

I need to take you back a couple of centuries.

我要带大家回到十九世纪。

In 1871, in a letter to his friend Joseph Hooker,

1871年，查尔斯·达尔文在信中

Charles Darwin suggested:

对他的朋友约瑟夫·虎克说：

"What if life started in some warm little pond

“如果生命是在一些 温暖的小池塘里诞生呢——

with all sort of chemicals

池塘里有各种化学物质，

still ready to undergo more complex changes?"

已准备好进行更复杂的进化呢？”

Well, we know of warm little ponds. We call them "hot springs."

我们知道这些温暖 的小池塘指的是“温泉”。

In these environments, you have hot water

在这类环境中，有热水，

dissolving minerals from the underlying rocks.

从底下的岩石里溶解出矿物质。

This solution mixes with organic compounds

这种液体与有机化合物混合，

and results in a kind of chemical factory,

形成了某种化学环境，

而研究人员已证明这种化学环境 可以产生简单的细胞结构，

which researchers have shown can manufacture simple cellular structures

这种细胞结构就是 迈向生命起源的第一步。

that are the first steps toward life.

But 100 years after Darwin's letter,

但达尔文写出这封信 之后的一百年，

deep-sea hydrothermal vents, or hot vents, were discovered in the ocean.

海洋里发现了 深海热液喷口，即热泉。

And these are also chemical factories.

这些也是化学环境。

This one is located along the Tonga volcanic arc,

这一个位于太平洋海平面以下

1,100 meters below sea level in the Pacific Ocean.

1100 米的汤加火山弧。

The black smoke that you see billowing out of these chimneylike structures

从这些烟囱一样的结构里 飘出的“黑烟”，

is also mineral-rich fluid,

也是富含矿物质的液体，

which is being fed off by bacteria.

是细菌的食物来源。

And since the discovery of these deep-sea vents,

自从发现了这些深海热泉，

the favored scenario for an origin of life has been in the ocean.

生命起源地的说法就聚焦在海洋。

And this is for good reason:

这是很合理的：

deep-sea vents are well-known in the ancient rock record,

深海热泉在古岩石记录中很常见，

and it's thought that the early Earth had a global ocean

通常认为地球早期 整体被海洋覆盖，

and very little land surface.

陆地表面极少。

So the probability that deep-sea vents were abundant on the very early Earth

所以，地球最初拥有大量深海热泉，

与之非常符合的情况是

fits well with an origin of life

in the ocean.

生命在海洋里起源。

However ...

但是——

our research in the Pilbara provides and supports

我们在皮尔巴拉的研究给出了

an alternative perspective.

另一种视角和证据。

After three years, finally, we were able to show that, in fact,

三年后，我们终于能证明，实际上，

our little rock was geyserite.

这块小石头就是硅华。

So this conclusion suggested not only did hot springs exist

这个结论说明， 不仅皮尔巴拉有 35 亿年历史

的火山里有温泉，

in our 3.5 billion-year-old volcano in the Pilbara,

而且意味着，在地球的地质记录中，

but it pushed back evidence for life living on land in hot springs

in the geological record of Earth

生命在陆地的热泉中存活的证据，

by three billion years.

向前推了 30 亿年。

And so, from a geological perspective,

所以，从地质角度来看，

Darwin's warm little pond is a reasonable origin-of-life candidate.

达尔文说的小池塘 是合理的生命起源地。

Of course, it's still debatable how life began on Earth,

当然，地球生命起源 的方式仍有待探讨，

and it probably always will be.

也许可以永远争论下去。

But it is clear that it's flourished;

但有一点很清楚， 生命已经蓬勃发展起来；

it has diversified,

它变得多样了，

and it has become ever more complex.

还越来越复杂。

Eventually, it reached the age of the human,

最终，到达了人类的时代，

人类这个物种开始质疑自身的存在，

a species that has begun to question its own existence

and the existence of life elsewhere:

也质疑外星球生命的存在：

Is there a cosmic community waiting to connect with us,

有宇宙联盟要与我们联系吗，

or are we all there is?

还是宇宙只有人类孤单存在？

A clue to this puzzle again comes from the ancient rock record.

关于这个问题的线索 再次出现在古岩石记录中。

At about 2.5 billion years ago,

大约 25 亿年前，

there is evidence that bacteria had begun to produce oxygen,

有证据表明， 细菌已经开始产生氧气，

kind of like plants do today.

有点像现在的植物产生氧气。

Geologists refer to the period that followed

地质学家把随后的那段时期

as the Great Oxidation Event.

称为“大氧化事件”。

It is implied from rocks called banded iron formations,

这一推测是从称为 带状铁形成区的岩石里得出的，

many of which can be observed as hundreds-of-meter-thick packages of rock

这种层层堆叠的岩石大多几百米厚，

which are exposed in gorges

位于澳大利亚西部，

that carve their way through the Karijini National Park

在横穿卡瑞吉尼国家公园的

in Western Australia.

峡谷里可以看到。

The arrival of free oxygen allowed two major changes to occur on our planet.

游离氧的到来让我们的星球 发生了两个重大变化。

First, it allowed complex life to evolve.

首先，氧气让复杂生命得以进化。

You see, life needs oxygen to get big and complex.

生命需要氧气来变大、变复杂。

And it produced the ozone layer, which protects modern life

氧气还制造了臭氧层， 它保护现代生命

from the harmful effects of the sun's UVB radiation.

不受阳光中波紫外线辐射的伤害。

So in an ironic twist, microbial life made way for complex life,

讽刺的是，微生物 艰难进化成复杂生命，

and in essence, relinquished its three-billion-year reign

在这颗星球上耗费了

over the planet.

30 亿年的时光。

Today, we humans dig up fossilized complex life

今天，我们人类把变成化石的 复杂生命挖出来，

and burn it for fuel.

把它们当燃料烧掉。

This practice pumps vast amounts of carbon dioxide into the atmosphere,

这种行为会释放出 大量二氧化碳到大气，

and like our microbial predecessors,

就像我们的微生物祖先一样，

我们已经开始让这颗星球 发生了重大变化。

we have begun to make substantial changes to our planet.

And the effects of those are encompassed by global warming.

这些改变的结果包括全球变暖。

Unfortunately, the ironic twist here could see the demise of humanity.

不幸的是，这个讽刺 会指向人类的终结。

And so maybe the reason we aren't connecting with life elsewhere,

也许我们联系不到外星生物、

intelligent life elsewhere,

联系不到外星智慧生物的原因，

is that once it evolves,

是一旦智慧生物进化了，

it extinguishes itself quickly.

就会很快自取灭亡。

If the rocks could talk,

如果岩石能说话，

I suspect they might say this:

我感觉它们会说：

life on Earth is precious.

地球上的生命是宝贵的。

It is the product of four or so billion years

它的诞生用了大约 40 亿年，

of a delicate and complex co-evolution

经历了生命与地球之间

between life and Earth,

精细复杂的共同进化，

of which humans only represent the very last speck of time.

而人类只在这 40 亿年 的最后一瞬间存在过。

You can use this information as a guide or a forecast --

这些信息可以为你 提供指引或预测——

or an explanation as to why it seems so lonely in this part of the galaxy.

或者说是解释，为什么 银河系的地球如此孤单。

But use it to gain some perspective

但是，通过这些信息多想想吧，

about the legacy that you want to leave behind

在这个我们称为家园的星球上，

on the planet that you call home.

人类要留下些什么。

Thank you.

谢谢你们。

(Applause)

（掌声）