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改变我们生命起源理论的古老岩石

发布者: 五毒 | 发布时间: 2022-8-4 15:30| 查看数: 103| 评论数: 0|



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?

地球的寿命有46亿年,但人类的寿命还不到100年。那我们为什么要关心地球历史呢,它那么遥远,好像与我们的生活完全无关。就我们所知,在太阳系里,只有地球拥有灿烂的生命,也只有地球能提供让人类存活的环境。为什么偏偏是地球?

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.

我们知道地球是独一无二的,它有板块构造、表面有液体水、还有富含氧气的大气层。但并不是一直这样,因为古岩石记录了地球演化过程中的每个关键时刻。观察古岩石的最佳去处之一,是澳大利亚西部的皮尔布拉。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。

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,说起古生命时,我们想到的是剑龙,或者一种鱼爬到了陆地上。但我说的古生命,是简单微生物,比如细菌。它们的化石通常是层叠的岩石结构,称为叠层石。地球出现生命的前30亿年里,化石记录中几乎只能见到这种简单的生命形式。在化石记录中寻找人类的踪迹,只能追踪到几万年前。

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.

从化石记录中我们了解到,细菌生命开始得很早,大约35至40亿年前就存在了。而比这个时间更久的岩石,要么被破坏了,要么随板块运动过度变形。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。回到皮尔布拉的古火山地貌。我当时完全不知道,我们在这里的研究会给生命起源之谜提供另一个线索。

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.

那是我第一次到这里实地考察,在整整一周的地图绘制项目快要结束时,我发现了一件不寻常的东西。这一堆纹路横生的石头,其实是叠层石。在这一堆的中间,是一块小小的罕见的岩石,像小孩的手那么大。我们花了六个月才得以在显微镜下观察它,当时我的一位老师,马尔科姆·沃尔特,提出这石头像硅华。

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."

硅华是一种岩石类型,它的形成地只在热泉池里面和边缘周围。为了让各位理解硅华的重要,我要带大家回到十九世纪。1871年,查尔斯·达尔文在信中对他的朋友约瑟夫·虎克说:“如果生命是在一些温暖的小池塘里诞生呢——池塘里有各种化学物质,已准备好进行更复杂的进化呢?”我们知道这些温暖的小池塘。我们称它们为“温泉”。

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.

在这类环境中,有热水,从底下的岩石里溶解出矿物质。这种液体与有机化合物混合,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,这种细胞结构就是迈向生命起源的第一步。但达尔文写出这封信之后的一百年,海洋里发现了深海热液喷口,即热泉。这些也是化学环境。

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.

这一个位于太平洋海平面以下1100米的汤加火山弧。从这些烟囱一样的结构里飘出的“黑烟”,也是富含矿物质的液体,是细菌的食物来源。自从发现了这些深海热泉,生命起源地的说法就聚焦在海洋。这是很合理的:深海热泉在古岩石记录中很常见,通常认为地球早期整体被海洋覆盖,陆地表面极少。

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,地球最初拥有大量深海热泉,与之非常符合的情况是生命在海洋里起源。但是——我们在皮尔巴拉的研究给出了另一种视角和证据。三年后,我们终于能证明,实际上,这块小石头就是硅华。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,而且意味着,在地球的地质记录中,生命在陆地的热泉中存活的证据,向前推了30亿年。

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,从地质角度来看,达尔文说的小池塘是合理的生命起源地。当然,地球生命起源的方式仍有待探讨,也许可以永远争论下去。但有一点很清楚,生命已经蓬勃发展起来。它变得多样了,还越来越复杂。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,也质疑外星球生命的存在:有宇宙联盟要与我们联系吗,还是宇宙只有人类孤单存在?

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.

关于这个问题的线索再次出现在古岩石记录中。大约25亿年前,有证据表明,细菌已经开始产生氧气,有点像现在的植物产生氧气。地质学家把随后的那段时期称为“大氧化事件”。这一推测是从称为带状铁形成区的岩石里得出的,这种层层堆叠的岩石大多几百米厚,位于澳大利亚西部,在横穿卡瑞吉尼国家公园的峡谷里可以看到。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. 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,氧气让复杂生命得以进化。生命需要氧气来变大、变复杂。氧气还制造了臭氧层,它保护现代生命不受阳光中波紫外线辐射的伤害。讽刺的是,微生物艰难进化成复杂生命,在这颗星球上耗费了30亿年的时光。今天,我们人类把变成化石的复杂生命挖出来,把它们当燃料烧掉。

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.

这种行为会释放出大量二氧化碳到大气,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。这些改变的结果包括全球变暖。不幸的是,这个讽刺可能会指向人类的终结。也许我们联系不到外星生物、联系不到外星智慧生物的原因,是一旦智慧生物进化了,就会很快自取灭亡。如果岩石能说话,我感觉它们会说:地球上的生命是宝贵的。

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.

它的诞生用了大约40亿年,经历了生命与地球之间精细复杂的共同进化,而人类只在这40亿年的最后一瞬间存在过。这些信息可以为你提供指引或预测——或者说是解释,为什么银河系的地球如此孤单。但是,通过这些信息多想想吧,在这个我们称为家园的星球上,人类要留下些什么。


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