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地球上的生命究竟是何時何地開始的？長期以來ironic，科學(xué)家們一直認(rèn)為它是在 30 億年前出現(xiàn)在海洋中的——直到天體生物學(xué)家塔拉·德約基奇和她的團(tuán)隊在澳大利亞西部的沙漠中獲得了一個意想不到的發(fā)現(xiàn)。

演講者ironic：塔拉·德約基奇

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The Earth is 4.6 billion years old, but a human lifetime often lasts for less than 100 years. So why care about the history of our planet when the distant past seems so inconsequential to everyday life? You see, as far as we can tell, Earth is the only planet in our solar system known to have sparked life, and the only system able to provide life support for human beings. So why Earth?

地球的壽命有46億年ironic，但人類的壽命還不到100年。那ironic我們?yōu)槭裁匆P(guān)心地球歷史呢，它那么遙遠(yuǎn)，好像與我們的生活完全無關(guān)。就我們所知，在太陽系里，只有地球擁有燦爛的生命，也只有地球能提供讓人類存活的環(huán)境。為什么偏偏是地球？

We know Earth is unique for having plate tectonics, liquid water on its surface and an oxygen-rich atmosphere. But this has not always been the case,and we know this because ancient rocks have recorded the pivotal moments in Earth's planetary evolution. And one of the best places to observe those ancient rocks is in the Pilbara of Western Australia. The rocks here are 3.5 billion years old, and they contain some of the oldest evidence for life on the planet.

我們知道地球是獨一無二的，它有板塊構(gòu)造、表面有液體水、還有富含氧氣的大氣層。但并不是一直這樣，因為古巖石記錄了地球演化過程中的每個關(guān)鍵時刻。觀察古巖石的最佳去處之一，是澳大利亞西部的皮爾布拉。這里的巖石存在了35億年之久，其中藏著地球上最早期生命的證據(jù)。

Now, often when we think of early life, we might imagine a stegosaurus or maybe a fish crawling onto land. But the early life that I'm talking about is simple microscopic life, like bacteria. And their fossils are often preserved as layered rock structures, called stromatolites. This simple form of life is almost all we see in the fossil record for the first three billion years of life on Earth. Our species can only be traced back in the fossil record to a few hundred thousand years ago.

通常，說起古生命時，我們想到的是劍龍，或者一種魚爬到了陸地上。但我說的古生命，是簡單微生物，比如細(xì)菌。它們的化石通常是層疊的巖石結(jié)構(gòu)，稱為疊層石。地球出現(xiàn)生命的前30億年里，化石記錄中幾乎只能見到這種簡單的生命形式。在化石記錄中尋找人類的蹤跡，只能追蹤到幾萬年前。

We know from the fossil record, bacteria life had grabbed a strong foothold by about 3.5 to four billion years ago. The rocks older than this have been either destroyed or highly deformed through plate tectonics.So what remains a missing piece of the puzzle is exactly when and how life on Earth began. Here again is that ancient volcanic landscape in the Pilbara. Little did I know that our research here would provide another clue to that origin-of-life puzzle.

從化石記錄中我們了解到，細(xì)菌生命開始得很早，大約35至40億年前就存在了。而比這個時間更久的巖石，要么被破壞了，要么隨板塊運動過度變形。所以遺留下來一個待解決的難題就是，地球上的生命到底是什么時間開始的?；氐狡柌祭墓呕鹕降孛病Ｎ耶?dāng)時完全不知道，我們在這里的研究會給生命起源之謎提供另一個線索。

It was on my first field trip here, toward the end of a full, long week mapping project, that I came across something rather special. Now, what probably looks like a bunch of wrinkly old rocks are actually stromatolites.And at the center of this mound was a small, peculiar rock about the size of a child's hand. It took six months before we inspected this rock under a microscope, when one of my mentors at the time, Malcolm Walter, suggested the rock resembled geyserite.

那是我第一次到這里實地考察，在整整一周的地圖繪制項目快要結(jié)束時，我發(fā)現(xiàn)了一件不尋常的東西。這一堆紋路橫生的石頭，其實是疊層石。在這一堆的中間，是一塊小小的罕見的巖石，像小孩的手那么大。我們花了六個月才得以在顯微鏡下觀察它，當(dāng)時我的一位老師，馬爾科姆·沃爾特，提出這石頭像硅華。

Geyserite is a rock type that only forms in and around the edges of hot spring pools. Now, in order for you to understand the significance of geyserite, I need to take you back a couple of centuries. In 1871, in a letter to his friend Joseph Hooker, Charles Darwin suggested: "What if life started in some warm little pond with all sort of chemicals still ready to undergo more complex changes?" Well, we know of warm little ponds. We call them "hot springs."

硅華是一種巖石類型，它的形成地只在熱泉池里面和邊緣周圍。為了讓各位理解硅華的重要，我要帶大家回到十九世紀(jì)。1871年，查爾斯·達(dá)爾文在信中對他的朋友約瑟夫·虎克說：“如果生命是在一些溫暖的小池塘里誕生呢——池塘里有各種化學(xué)物質(zhì)，已準(zhǔn)備好進(jìn)行更復(fù)雜的進(jìn)化呢？”我們知道這些溫暖的小池塘。我們稱它們?yōu)椤皽厝薄?/p>

In these environments, you have hot water dissolving minerals from the underlying rocks. This solution mixes with organic compounds and results in a kind of chemical factory, which researchers have shown can manufacture simple cellular structures that are the first steps toward life. But 100 years after Darwin's letter, deep-sea hydrothermal vents, or hot vents, were discovered in the ocean. And these are also chemical factories.

在這類環(huán)境中，有熱水，從底下的巖石里溶解出礦物質(zhì)。這種液體與有機(jī)化合物混合，形成了某種化學(xué)環(huán)境，而研究人員已證明這種化學(xué)環(huán)境可以產(chǎn)生簡單的細(xì)胞結(jié)構(gòu)，這種細(xì)胞結(jié)構(gòu)就是邁向生命起源的第一步。但達(dá)爾文寫出這封信之后的一百年，海洋里發(fā)現(xiàn)了深海熱液噴口，即熱泉。這些也是化學(xué)環(huán)境。

This one is located along the Tonga volcanic arc, 1,100 meters below sea level in the Pacific Ocean. The black smoke that you see billowing out of these chimneylike structures is also mineral-rich fluid, which is being fed off by bacteria. And since the discovery of these deep-sea vents, the favored scenario for an origin of life has been in the ocean. And this is for good reason: deep-sea vents are well-known in the ancient rock record, and it's thought that the early Earth had a global ocean and very little land surface.

這一個位于太平洋海平面以下1100米的湯加火山弧。從這些煙囪一樣的結(jié)構(gòu)里飄出的“黑煙”，也是富含礦物質(zhì)的液體，是細(xì)菌的食物來源。自從發(fā)現(xiàn)了這些深海熱泉，生命起源地的說法就聚焦在海洋。這是很合理的：深海熱泉在古巖石記錄中很常見，通常認(rèn)為地球早期整體被海洋覆蓋，陸地表面極少。

So the probability that deep-sea vents were abundant on the very early Earth fits well with an origin of life in the ocean. However ... our research in the Pilbara provides and supports an alternative perspective. After three years, finally, we were able to show that, in fact, our little rock was geyserite. So this conclusion suggested not only did hot springs exist in our 3.5 billion-year-old volcano in the Pilbara, but it pushed back evidence for life living on land in hot springs in the geological record of Earth by three billion years.

所以，地球最初擁有大量深海熱泉，與之非常符合的情況是生命在海洋里起源。但是——我們在皮爾巴拉的研究給出了另一種視角和證據(jù)。三年后，我們終于能證明，實際上，這塊小石頭就是硅華。這個結(jié)論說明，不僅皮爾巴拉有35億年歷史的火山里有溫泉，而且意味著，在地球的地質(zhì)記錄中，生命在陸地的熱泉中存活的證據(jù)，向前推了30億年。

And so, from a geological perspective, Darwin's warm little pond is a reasonable origin-of-life candidate. Of course, it's still debatable how life began on Earth, and it probably always will be. But it is clear that it's flourished.It has diversified, and it has become ever more complex.Eventually, it reached the age of the human, a species that has begun to question its own existence and the existence of life elsewhere: Is there a cosmic community waiting to connect with us, or are we all there is?

所以，從地質(zhì)角度來看，達(dá)爾文說的小池塘是合理的生命起源地。當(dāng)然，地球生命起源的方式仍有待探討，也許可以永遠(yuǎn)爭論下去。但有一點很清楚，生命已經(jīng)蓬勃發(fā)展起來。它變得多樣了，還越來越復(fù)雜。最終，到達(dá)了人類的時代，人類這個物種開始質(zhì)疑自身的存在，也質(zhì)疑外星球生命的存在：有宇宙聯(lián)盟要與我們聯(lián)系嗎，還是宇宙只有人類孤單存在？

A clue to this puzzle again comes from the ancient rock record. At about 2.5 billion years ago, there is evidence that bacteria had begun to produce oxygen, kind of like plants do today. Geologists refer to the period that followed as the Great Oxidation Event. It is implied from rocks called banded iron formations, many of which can be observed as hundreds-of-meter-thick packages of rock which are exposed in gorges that carve their way through the Karijini National Park in Western Australia. The arrival of free oxygen allowed two major changes to occur on our planet.

關(guān)于這個問題的線索再次出現(xiàn)在古巖石記錄中。大約25億年前，有證據(jù)表明，細(xì)菌已經(jīng)開始產(chǎn)生氧氣，有點像現(xiàn)在的植物產(chǎn)生氧氣。地質(zhì)學(xué)家把隨后的那段時期稱為“大氧化事件”。這一推測是從稱為帶狀鐵形成區(qū)的巖石里得出的，這種層層堆疊的巖石大多幾百米厚，位于澳大利亞西部，在橫穿卡瑞吉尼國家公園的峽谷里可以看到。游離氧的到來讓我們的星球發(fā)生了兩個重大變化。

First, it allowed complex life to evolve. You see, life needs oxygen to get big and complex. And it produced the ozone layer, which protects modern life from the harmful effects of the sun's UVB radiation. So in an ironic twist, microbial life made way for complex life,and in essence, relinquished its three-billion-year reign over the planet. Today, we humans dig up fossilized complex life and burn it for fuel.

首先，氧氣讓復(fù)雜生命得以進(jìn)化。生命需要氧氣來變大、變復(fù)雜。氧氣還制造了臭氧層，它保護(hù)現(xiàn)代生命不受陽光中波紫外線輻射的傷害。諷刺的是，微生物艱難進(jìn)化成復(fù)雜生命，在這顆星球上耗費了30億年的時光。今天，我們?nèi)祟惏炎兂苫膹?fù)雜生命挖出來，把它們當(dāng)燃料燒掉。

This practice pumps vast amounts of carbon dioxide into the atmosphere, and like our microbial predecessors, we have begun to make substantial changes to our planet.And the effects of those are encompassed by global warming. Unfortunately, the ironic twist here could see the demise of humanity. And so maybe the reason we aren't connecting with life elsewhere, intelligent life elsewhere, is that once it evolves, it extinguishes itself quickly. If the rocks could talk, I suspect they might say this: life on Earth is precious.

這種行為會釋放出大量二氧化碳到大氣，就像我們的微生物祖先一樣，我們已經(jīng)開始讓這顆星球發(fā)生了重大變化。這些改變的結(jié)果包括全球變暖。不幸的是，這個諷刺可能會指向人類的終結(jié)。也許我們聯(lián)系不到外星生物、聯(lián)系不到外星智慧生物的原因，是一旦智慧生物進(jìn)化了，就會很快自取滅亡。如果巖石能說話，我感覺它們會說：地球上的生命是寶貴的。

It is the product of four or so billion years of a delicate and complex co-evolution between life and Earth, of which humans only represent the very last speck of time. You can use this information as a guide or a forecast -- or an explanation as to why it seems so lonely in this part of the galaxy. But use it to gain some perspective about the legacy that you want to leave behind on the planet that you call home.

它的誕生用了大約40億年，經(jīng)歷了生命與地球之間精細(xì)復(fù)雜的共同進(jìn)化，而人類只在這40億年的最后一瞬間存在過。這些信息可以為ironic你提供指引或預(yù)測——或者說是解釋，為什么銀河系的地球如此孤單。但是，通過這些信息多想想吧，在這個我們稱為家園的星球上，人類要留下些什么。

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