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

譯者: Lilian Chiu 審譯者: 易帆 余

The Earth is 4.6 billion years old,

地球的年齡是四十六億歲，

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

但人類的生命通常不到一百年。

So why care about the history of our planet

所以，為什麼要在乎地球的歷史，

when the distant past seems so inconsequential to everyday life?

畢竟遙遠的過去對日常生活 似乎也無足輕重？

You see, as far as we can tell,

要知道，根據可得資訊，

Earth is the only planet in our solar system

在我們的太陽系中，只有地球

known to have sparked life,

擁有璀璨的生命，

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

也只有這個星球能提供 支持人類生命的系統。

So why Earth?

所以，為什麼是地球？

We know Earth is unique for having plate tectonics,

我們知道地球獨一無二的 特徵包括它的板塊構造、

liquid water on its surface

表面的液態水，

and an oxygen-rich atmosphere.

以及富含氧氣的大氣。

But this has not always been the case,

但並非一直都是如此的，

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

我們知道這一點， 是因為古老的岩石記錄了

地球演化過程中的每個關鍵片刻。

in Earth's planetary evolution.

And one of the best places to observe those ancient rocks

觀察這些古老岩石 最好的地方之一，

is in the Pilbara of Western Australia.

就是澳洲西部的皮爾布拉。

The rocks here are 3.5 billion years old,

這裡的岩石有三十五億年的歷史，

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

它們內含有地球上 最早的生命的證據。

Now, often when we think of early life,

通常，當我們談到古老生命時，

we might imagine a stegosaurus

我們會想像到劍龍，

or maybe a fish crawling onto land.

或是某種魚類爬到陸地上。

But the early life that I'm talking about

但我所談的古老生命

is simple microscopic life, like bacteria.

是簡單的微生命，比如細菌。

And their fossils are often preserved as layered rock structures,

它們的化石通常會以層疊 岩石結構的形式保存下來，

called stromatolites.

稱為疊層石。

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

在地球有生命出現起的 最初三十億年，

我們在化石記錄中，看到的 大部分是簡單形式的生命。

for the first three billion years of life on Earth.

Our species can only be traced back in the fossil record

化石紀錄只能追溯我們人類物種

to a few hundred thousand years ago.

到幾十萬年前。

We know from the fossil record,

我們從化石記錄可以知道，

bacteria life had grabbed a strong foothold

細菌生命在大約 三十五到四十億年前

by about 3.5 to four billion years ago.

就立下穩固的基礎。

The rocks older than this have been either destroyed

比這更古老的岩石 若不是被摧毀了，

or highly deformed through plate tectonics.

就是因為板塊構造而嚴重變形。

So what remains a missing piece of the puzzle

所以，拼圖仍然少了一片，

is exactly when and how life on Earth began.

那片就是：地球是 何時、如何開始的？

Here again is that ancient volcanic landscape in the Pilbara.

回到皮爾布拉的古老火山地景。

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

我當時並不知道我們的研究 會提供另一條線索

to that origin-of-life puzzle.

來破解生命源頭之謎。

It was on my first field trip here,

那是我第一次實地勘察，

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

在整整一週漫長的 製圖專案接近尾聲時，

that I came across something rather special.

我發現了一樣蠻特別的東西。

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

外表看起來像非常 古老的一堆岩石，

are actually stromatolites.

其實是疊層石。

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

在這一堆奇怪的小岩石的中心，

about the size of a child's hand.

大小接近孩子的手。

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

我們花了六個月的時間， 在顯微鏡底下觀察這塊岩石，

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

當時，我的導師之一， 麥爾肯華特，

suggested the rock resembled geyserite.

覺得這塊岩石很像鈣礬石。

Geyserite is a rock type that only forms

鈣礬石這種岩石

只會在溫泉池的邊源出現。

in and around the edges of hot spring pools.

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

為了讓各位了解鈣礬石的重要性，

I need to take you back a couple of centuries.

我得帶各位回到幾世紀前。

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

1871 年，達爾文寫給

他的朋友約瑟夫胡克的信上指出：

Charles Darwin suggested:

"What if life started in some warm little pond

「有沒有可能生命始於 某個溫暖的小池子，

with all sort of chemicals

裡面有各種化學物質，

still ready to undergo more complex changes?"

隨時蓄勢待發準備好要做出 更複雜的改變？」

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

我們熟識這些溫暖的小池子， 稱之為「溫泉」。

In these environments, you have hot water

這些環境中有熱水

dissolving minerals from the underlying rocks.

從底下的岩石溶解出礦物質。

This solution mixes with organic compounds

這種溶液和有機化合物混合，

and results in a kind of chemical factory,

產生出了某種化學工廠，

which researchers have shown can manufacture simple cellular structures

研究者已經證明，

這個工廠會製造簡單的細胞結構，

that are the first steps toward life.

是生命的最初起源。

But 100 years after Darwin's letter,

但在達爾文的那封信之後一百年，

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

在海洋中發現了深海溫泉。

And these are also chemical factories.

它們也是化學工廠。

This one is located along the Tonga volcanic arc,

這個工廠的位置沿著湯加火山弧，

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

在太平洋海平面下一千一百公尺。

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

各位可以看到，從這些 像煙囪的結構噴出來的黑煙

is also mineral-rich fluid,

也是富含礦物質的液體，

which is being fed off by bacteria.

細菌會從這裡取食。

And since the discovery of these deep-sea vents,

自從發現了這些深海溫泉之後，

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

比較熱門的生命起源 說法就是海洋。

And this is for good reason:

背後有很好的理由：

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

從古老的岩石記錄中就能 清楚知道深海溫泉的存在，

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

一般認為，早期的地球 有一個全球性的海洋，

and very little land surface.

陸地表面很少。

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

所以，很有可能，古老的地球上 有很多深海溫泉，

fits well with an origin of life

這點非常符合生命 起源於海洋的說法。

in the ocean.

However ...

然而……

our research in the Pilbara provides and supports

我們在皮爾布拉的研究提供

且支持了另一種替代的觀點。

an alternative perspective.

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

三年後，

我們終於得以證明，事實上，

our little rock was geyserite.

我們的岩石是鈣礬石。

So this conclusion suggested not only did hot springs exist

所以，這個結論不只 意味著三十五億年前

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

溫泉存在於皮爾布拉的火山中，

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

也意味著，地質記錄中證明

生命存在於陸地溫泉的證據

in the geological record of Earth

by three billion years.

被推回了三十億年。

And so, from a geological perspective,

所以，從地質的觀點來看，

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

達爾文的溫暖小池子

的確是合理的生命起源選項之一。

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

當然「地球的生命起源」 仍然有爭論空間，

and it probably always will be.

可能永遠都會有。

But it is clear that it's flourished;

但，很顯然，生命興起了， 生命變多樣了，

it has diversified,

and it has become ever more complex.

且生命也變得前所未有的複雜。

Eventually, it reached the age of the human,

最終，到了人類的時代，

a species that has begun to question its own existence

當我們開始質疑自身的存在

and the existence of life elsewhere:

以及其他地方是否有生命存在時，

Is there a cosmic community waiting to connect with us,

不禁會問：是否有個宇宙群落 等著和我們連結，

or are we all there is?

或者宇宙中只有我們？

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

同樣的，這個謎題的一條線索 也來自古老岩石記錄。

At about 2.5 billion years ago,

大約二十五億年前，

there is evidence that bacteria had begun to produce oxygen,

有證據顯示細菌開始產生氧氣，

kind of like plants do today.

有點像現今的植物。

Geologists refer to the period that followed

地質學家把接在後面的時期稱為

as the Great Oxidation Event.

大氧化事件。

It is implied from rocks called banded iron formations,

源自所謂的帶狀鐵礦層，

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

許多帶狀鐵礦層看起來是 數百公尺厚的岩石組，

which are exposed in gorges

一路從澳洲西部的卡瑞吉尼國家公園

that carve their way through the Karijini National Park

縱切過來的峽谷中就可以看到。

in Western Australia.

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

單體氧（游離氧）的出現， 在地球上帶來兩個重大改變。

First, it allowed complex life to evolve.

第一，它讓複雜的生命能夠演化。

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

生命需要氧才能變大、變複雜。

And it produced the ozone layer, which protects modern life

它能製造臭氧層，保護現代生命

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

不被太陽的中波紫外線輻射傷害。

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

經過出乎意料的曲折發展， 微生物為複雜的生命開了一條路，

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

本質上，也交出了在地球上 三十億年的統治權。

over the planet.

Today, we humans dig up fossilized complex life

現今，我們人類把這些 變成化石的複雜生命

and burn it for fuel.

挖出來將之燃燒成為燃料。

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

這個做法將大量的 二氧化碳送入大氣中，

and like our microbial predecessors,

就和我們的微生物前輩一樣，

we have begun to make substantial changes to our planet.

人類也開始在地球上 造成了實質的變化。

And the effects of those are encompassed by global warming.

那些改變的效應包含全球暖化。

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

不幸的是，這次 出乎意料的曲折發展

有可能會導致人類的滅亡。

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

所以，也許我們沒有 在其他地方找到生命的原因，

intelligent life elsewhere,

沒找到智慧生命的原因，

is that once it evolves,

是因為一旦智慧生命演化之後 很快就會讓自己滅絕。

it extinguishes itself quickly.

If the rocks could talk,

如果岩石會說話，

I suspect they might say this:

我猜它們可能會說：

life on Earth is precious.

地球上的生命是很珍貴的。

It is the product of four or so billion years

生命的誕生，

是生命和地球經歷了四十億年

of a delicate and complex co-evolution

細膩而複雜的演化共同形成的。

between life and Earth,

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

人類存在的時間只是這段 共同演化的最後一小截而已。

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

這些資訊可以拿來 當作指引或者預測——

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

或者用來解釋為什麼地球上的生命， 在銀河系裡看起來是如此的孤單。

But use it to gain some perspective

但，透過這些資訊想想，

about the legacy that you want to leave behind

在這個稱為「家」的地球上，

on the planet that you call home.

我們人類要留給後代的是甚麼。

Thank you.

謝謝。

(Applause)

（掌聲）