【英翻】《大西洋月刊》：遇见地底生物
Meet the Endoterrestrials
遇见地底生物
Hydrogen sulfide—a gas found in sewers, in your intestines, and, apparently, underground in Oman—is produced by microbes living in the absence of oxygen. Deprived of that life-giving gas, they pull a trick that no animal on Earth can do: They breathe something else. In other words, they burn their food using some other chemical that is available underground.
硫化氢是一种存在于下水道、肠道——显然还有阿曼地下的气体，它是由生活在缺氧环境中的微生物产生的。没有了那种能维持生命的气体，它们就会做出地球上任何动物都做不到的事情：呼吸其他东西。换句话说，它们用地下可利用的其他化学物质燃烧食物。
The sections of core brought up so far offered clues about what they might be breathing. The gassy core was crisscrossed by bands of orange-brown stone—marking the places where hot magma had spurted through deep fissures in the Earth millions of years before, when this rock lay miles underground.
到目前为止发现的岩芯提供了它们可能是怎样呼吸的线索。这个冒气的岩芯上面是纵横交错的橘黄色的条纹，这些条纹标识出了数百万年前炽热的岩浆从地下几英里处的深裂缝中喷出来的地方。
Those bands of fossil magma would have gradually bled their chemical components into the groundwater—including a molecule called sulfate, which consists of a single sulfur atom studded with four oxygen atoms. The microbes were probably using this molecule to digest hydrogen, said Templeton: “They eat the hydrogen and they breathe the sulfate.” And then, they exhale fart gas.
这些化石岩浆带的化学成分会逐渐渗入地下水，其中包括一种叫做硫酸盐的分子，它由一个硫原子和四个氧原子组成。坦普尔顿说，这些微生物可能利用这种分子来消化氢，“它们吃掉氢，呼吸硫酸盐”。然后，它们呼出的是屁。
Hydrogen sulfide isn’t just stinky. It is also toxic. So the very microbes that produce it also run the risk of poisoning themselves as it accumulates underground. How did they avoid doing so? Once again, the rock provided clues.
硫化氢不仅是臭的，它还是有毒的。因此，产生这种物质的微生物也有让自己中毒的危险，因为它会在地下积聚。它们是如何避免这种结果的呢？岩石再次提供了线索。
As drilling continued over the next several days, the black goo petered out. Each new section of core was dry and stink-free. But the stone itself had changed: Its mosaic of veins and serpentine minerals had darkened into shades of gray and black, like a plaid shirt soaked in ink.
在接下来的几天里，随着钻探的继续，黑色粘稠物逐渐消失。每一段岩芯都是干燥无味的。但是石头本身已经发生了变化：它那由纹理和蛇纹石化矿物组成的马赛克已经变成了灰色和黑色，就像一件浸透了墨水的格子衬衫。
“All of that blackening is a bio-product,” Templeton said one afternoon, as she and her research associate, Eric Ellison, crowded inside a cramped laboratory trailer, packing samples of rock to send home. Some of the rocks sat in a sealed Plexiglass box, and Ellison handled them with his hands inserted through gloves mounted in the walls of the box—giving the appearance that the rocks contained something sinister. But the precaution wasn’t intended to protect humans; it was meant to keep the delicate microbes out of contact with oxygen.
“所有这些变黑的结果都是一种生物产品，”一天下午，邓普顿和她的研究助理埃里克·埃里森挤在一辆狭窄的实验室拖车里，她如此说道。他们正在打包岩石样本，准备送回家。有些石头放在一个密封的有机玻璃盒子里，埃利森把戴着手套的手伸进盒子取石头，看上去石头里藏着什么凶恶的东西。但这种预防措施并不是为了保护人类；它的目的是让这些脆弱的微生物远离氧气。
Templeton speculated that the microbes had stained the most recent rock samples: The hydrogen sulfide they exhaled had reacted with iron in the surrounding stone, creating iron sulfide—a harmless black mineral. The pyrite minerals we’d seen earlier were also composed of iron and sulfide, and could have formed the same way.
坦普尔顿推测这些微生物对最近的岩石样本进行了染色：它们呼出的硫化氢与周围岩石中的铁发生了反应，生成了硫化铁——一种无害的黑色矿物。我们之前看到的黄铁矿矿物也是由铁和硫化物组成的，它也可能是以同样的方式形成的。
These black minerals are more than an academic curiosity. They provide a glimpse of how microbes have not only survived inside the Earth’s crust, but also transformed it, in some cases forming minerals that might not otherwise exist.
这些黑色矿物不仅仅是学术上的奇闻轶事。它们让我们得以一窥微生物是如何在地壳内部生存下来的，它们是如何改造地壳的，在某些情况下，它们形成了原本不可能存在的矿物质。
Some of the world’s richest deposits of iron, lead, zinc, copper, silver, and other metals formed when hydrogen sulfide latched onto metals that had dissolved deep underground. The sulfide locked the metals in place, concentrating them into minerals that accumulated for millions of years—until they were exhumed by miners. The hydrogen sulfide that formed those ores often came from volcanic sources, but in some cases, it came from microbes.
一些世界上含量最丰富的矿藏——铁、铅、锌、铜、银和其他的金属——是在硫化氢与溶解在地下深处的金属结合时形成的。硫化物将金属固定在原地，将它们浓缩成矿物，这些矿物积累了数百万年，直到被矿工挖掘出来。形成这些矿石的硫化氢通常来自火山，但在某些情况下，它来自微生物。
Robert Hazen, a mineralogist and astrobiologist at the Carnegie Institution in Washington, D.C., believes that more than half of Earth’s minerals owe their existence to life—to the roots of plants, to corals and diatoms, and even to subsurface microbes. He has even speculated that the world’s seven continents may owe their existence, in part, to microbes gnawing on rocks.
罗伯特·哈森是华盛顿卡内基研究所的矿物学家和天体生物学家。他认为，地球上一半以上的矿物的存在都归功于生命——植物的根、珊瑚和硅藻，甚至地下微生物。他甚至推测，世界上七大洲存在的部分原因可能就是微生物啃噬岩石。
Four billion years ago, Earth had no permanent land—just a few volcanic peaks jutting above the ocean. But microbes on the seafloor may have helped change that. They attacked iron-rich basalt rocks, much as they do today, converting the volcanic glass into clay minerals. Those clays melted more readily than other rocks. And once melted, they resolidified into a new kind of rock, a material lighter and fluffier than the rest of the planet: granite.
40亿年前，地球上没有永久性的陆地——只有几座火山山峰突出海面。但是海底的微生物可能帮助改变了这一点。它们攻击富含铁的玄武岩，就像它们今天所做的一样，将火山玻璃转化为粘土矿物。这些粘土比其他岩**容易熔化。一旦融化，它们就会重新凝固成一种新的岩石，一种比地球上的其他部分更轻、更松软的材料：花岗岩。
Those buoyant granites piled into heaps that rose above the ocean, creating the first permanent continents. This would have happened to some degree without the help of microbes, but Hazen suspects that they accelerated the process. “You can imagine microbes shifting the balance,” he says. “What we’re arguing is that microbes played a fundamental role.”
那些浮力大的花岗岩堆积在海面上，形成了第一个永久性的大陆。如果没有微生物的帮助，这种情况在某种程度上也是会发生的，但是哈森怀疑微生物加速了这一进程。“你可以想象微生物改变了平衡，”他说道，“我们认为微生物扮演了一个基本性的角色。”
The emergence of land had a profound effect on Earth’s evolution. Rocks exposed to the air broke down more quickly, releasing trace nutrients such as molybdenum, iron, and phosphorus into the oceans. These nutrients spurred the growth of photosynthetic algae, which absorbed carbon dioxide and exhaled oxygen. Just over 2 billion years ago, the first traces of oxygen appeared in Earth’s atmosphere. Five hundred and fifty million years ago, oxygen levels finally rose high enough to support the first primitive animals.
陆地的出现对地球的演化产生了深远的影响。暴露在空气中的岩石分解得更快，向海洋中释放微量营养物质，如钼、铁和磷。这些营养物质刺激了光合藻类的生长，光合藻类吸收二氧化碳并呼出氧气。就在20亿年前，地球大气中出现了最初的氧气痕迹。五亿五千万年前，氧气水平终于上升到足以支持第一批原始动物的水平。
Earth’s abundant water, and its optimal distance from the sun, made it a promising incubator for life. But its evolution into a paradise for intelligent, oxygen-breathing animals was never guaranteed. Microbes may have pushed our planet over an invisible tipping point—and toward the formation of continents, oxygen, and life as we know it.
地球上丰富的水，以及它与太阳的最佳距离，使它成为一个有希望的孕育生命的地方。但它能否进化成为了聪明的、呼吸氧气的动物的天堂却从未是确证无疑的。微生物可能已经把我们的星球推过了一个看不见的临界点——朝着我们所知道的大陆、氧气和生命的形态推进。
Even today, microbes continue to make, and remake, our planet from the inside out.
即使在今天，微生物仍然在从内到外地塑造和改造我们的星球。
In some ways, the microbe underworld resembles human civilization, with microbial “cities” built at the crossroads of commerce. In Oman, the thriving oasis of stinky, black microbes sat 100 feet underground, near the intersection of several large rock fractures—channels that allowed hydrogen and sulfate to trickle in from different sources.
在某些方面，微生物的地底社会与人类文明相似，微生物的“城市”建立在商业的十字路口。在阿曼，繁荣的臭气腾腾的黑色微生物绿洲位于地下100英尺处，它靠近几处大型岩石裂隙的交汇处——这些裂隙允许氢和硫酸盐从不同来源流过来。
Elisabetta Mariani, a structural geologist from the University of Liverpool in England, spent long days under the canopy, mapping these breaks in the rock. Late one morning, she called me over to see something special: a break cutting diagonally across a core, exposing two rock faces streaked in paper-thin layers of green-and-black serpentine.
英国利物浦大学的结构地质学家伊丽莎白花了很长时间在树冠下测绘岩石上的这些裂缝。一天上午的晚些时候，她叫我去看一些特别的东西：一条斜切岩芯的裂缝，其中露出了两块岩石的表面，上面布满了像纸一样薄的绿黑相间的蛇纹。
“Can you see here these grooves?” she asked, in English accented with her native Italian, pointing out scratches that raked the two serpentine faces. They showed that this was more than just a passive break; it was an active fault. “Two blocks of rocks have slipped past each other along this direction,” she said, gesturing along the grooves.
“你能看到这些凹槽吗？”她用带着母语意大利语口音的英语问道，同时指着那两块蛇形表面上的划痕。它们证明了这不仅仅是一次被动的断裂；这是一个活动断层。“两块岩石沿着这个方向相互滑过，”她指着凹槽说道。
Tullis Onstott, a geologist at Princeton University not affiliated with the Oman drilling, believes that such active faults may do more than just provide routes for food to move underground—they may actually produce food. In November 2017, Onstott and his colleagues began an audacious experiment. Starting from a tunnel 8,000 feet down in the Moab Khotsong gold mine in South Africa, they bored a new hole toward a fault that lay nearly half a mile deeper still. On August 5, 2014, the fault had sparked a magnitude-5.5 earthquake. By drilling into it, Onstott hoped to test the provocative idea that earthquakes supply food to the deep biosphere.
普林斯顿大学的地质学家图利斯·奥斯多特认为，这些活动断层不仅为食物在地下的移动提供了通道，它们还可能会生产食物。2017年11月，奥斯多特和他的同事们开始了一项大胆的实验。他们从南非摩押·霍特松金矿8000英尺深的一个隧道开始，朝着一个更深近半英里的断层挖了一个新洞。2014年8月5日，该断层引发了5.5级地震。通过钻探，奥斯托特希望测试这个具有颠覆性的想法，即地震为地层深处的生物圈提供了食物。
Scientists have long noticed that hydrogen gas seeps out of major faults such as the San Andreas in California. That gas is produced in part by a chemical reaction: Silicate minerals pulverized during a quake react with water and release hydrogen as a byproduct. For microbes sitting next to the fault, that reaction could result in something like a periodic sugar rush.
科学家们早就注意到氢气会从主要的断层中渗出，比如加州的圣安德烈亚斯断层。这种气体部分是由化学反应产生的：在地震中粉碎的硅酸盐矿物与水发生反应，释放出副产品氢。对于断层附近的微生物来说，这种反应可能会引发周期性的糖果大战。
In March 2018, four months after the drilling in the Moab Khotsong mine began, workers brought up a stone core that crossed the fault.
2018年3月，摩押·霍特松金矿开始钻探四个月后，工人们挖出了一段穿过断层的岩芯。
The rock along the fault was “pretty banged up,” says Onstott—torn with dozens of parallel fractures. The stone lining some of those cracks was crushed into fragile clay, marking recent earthquakes. Other cracks, filled with veins of white quartzite, marked older ruptures from thousands of years before.
奥斯多特说道：断层沿线的岩石“被撞得粉碎”，同时还有数十处平行的裂缝。其中一些裂缝里的石头被压成易碎的粘土，标志着最近发生的地震。其他的裂缝则填满了白色石英岩脉，标志着几千年前更古老的断裂。
Onstott is now searching those quartzite veins for fossilized cells and analyzing the rock for DNA, in hopes of finding out what kind of microbes—if any—inhabit the fault.
奥斯多特目前正在这些石英岩脉中寻找化石细胞，并对岩石进行DNA分析，希望能找到栖息在断层中的微生物(如果有的话)。
More importantly, he and his colleagues have kept the borehole open—monitoring water, gases, and microbes in the fault, and taking new samples each time there’s an aftershock. “You can then see whether or not there’s a gas release,” he says, “and whether or not there’s a change in the microbial community because they’re consuming the gas.”
更重要的是，他和他的同事们保持了钻孔的开放状态，监测断层中的水、气体和微生物，并在每次余震发生时采集新的样本。他说:“然后你就可以看到是否有气体释放出来，以及微生物群落是否因为消耗了气体而发生了变化。”
Even as Onstott awaits those results, he is starting to consider an even more radical possibility: that deep-dwelling microbes don’t just feed off of earthquakes, but might also trigger them. He believes that as microbes attack the iron, manganese, and other elements in the minerals that line the fault, they could weaken the rock—and prime the fault for its next big slip. Exploring that possibility would mean doing laboratory experiments to find out whether microbes in a fault can actually break down minerals quickly enough to affect seismic activity. With a scientist’s characteristic understatement, he contemplates the work ahead: “It’s a reasonable hypothesis to test.”
即使在奥斯多特等待这些结果的同时，他也已经开始考虑一种更激进的可能性：深海微生物不仅以地震为食，还可能引发地震。他相信，当微生物攻击沿断层排列的矿物中的铁、锰和其他元素时，它们会让岩石变得脆弱，并为下一次大滑坡做好准备。探索这种可能性意味着要进行实验室实验，以查明断层中的微生物是否能够迅速分解矿物质，从而影响到地震活动。带着科学家特有的轻描淡写，他思考着未来的工作：“这是一个需要验证的合理假设”。
By January 30, the drill in Wadi Lawayni had reached a depth of 200 feet. Its motor growled in the background as Templeton and her colleague, Eric Boyd, rested in camp chairs under an acacia tree. Strewn at their feet lay the signs of other travelers who had paused in this rare island of shade—nodules of camel dung, smooth and round like leathery plums.
到1月30日，瓦迪·拉瓦尼的钻井已经达到200英尺的深度。当坦普尔顿和她的同事埃里克·博伊德坐在一棵相思树下的野营椅上休息时，机器的马达在背景中轰鸣。在他们的脚下，散落着其他旅行者在这个罕见的阴岛停留过的痕迹——一堆堆光滑圆润的骆驼粪，就像闪耀着皮革般光泽的李子一样。
“We think that this is an environment that’s important for understanding the origins of life,” said Boyd, a geobiologist from Montana State University in Bozeman. That potential, he said, is part of what lured him and Templeton to these deep-earth rocks in Oman: “We like hydrogen.”
位于博兹曼的蒙大拿州立大学的地质学家博伊德说，“我们认为，这是一个对理解生命起源非常重要的环境。”他说，正是这种潜力吸引着他和坦普尔顿来到阿曼寻找这些深埋地下的岩石：“我们喜欢氢气”。
Both Boyd and Templeton believe that life on Earth started in an environment similar to that which lies a few yards beneath their camp chairs. They believe that life began within subsurface fractures, where iron-rich minerals gurgled out hydrogen gas as they reacted with water.
博伊德和坦普尔顿都相信，地球上的生命便始于一个类似于他们露营椅下面几码的环境中。他们认为生命起源于地下裂缝，富含铁的矿物与水发生反应时会喷出氢气。
Of all the chemical fuels that existed on Earth 4 billion years ago, hydrogen would have been one of the easiest for early, inefficient cells to metabolize. Hydrogen wasn’t only produced by serpentinization, either; it was also produced—and still is, today—by the radioactive decay of elements such as uranium, which constantly splits apart water molecules in the surrounding rock. Hydrogen is so labile, so willing to break apart, that it can even be digested using sluggish o****nts, like carbon dioxide or pure sulfur. DNA studies of millions of gene sequences suggest that the forerunner of all life on Earth—the “last universal common ancestor,” or LUCA—probably did use hydrogen as its food, and burned it with carbon dioxide. The same might be true for life in other worlds.
在40亿年前地球上存在的所有化学燃料中，氢是早期低效细胞最容易代谢的燃料之一。氢不仅是由蛇纹石化产生的；它也是由铀等元素的放射性衰变产生的，至今仍是如此。铀等元素不断地分解周围岩石中的水分子。氢是如此不稳定，如此容易分解，以至于它甚至可以被缓慢的氧化剂消化，如二氧化碳或纯硫。对数百万个基因序列的DNA研究表明，地球上所有生命的先驱者——“最后的共同祖先”(或称之为“卢卡”)——可能确实以氢气为食物，并将其与二氧化碳一起燃烧。其他世界的生命可能也是如此。
The iron minerals that exist here in Oman are common across the solar system, as is the process of serpentinization. The Reconnaissance Orbiter, a space probe now circling Mars, has mapped serpentine minerals on the Martian surface. The space probe Cassini has found chemical evidence of ongoing serpentinization deep within Saturn’s ice-covered moon, Enceladus. Serpentine-like minerals have been detected on the surface of Ceres, a dwarf planet that orbits the sun between Mars and Jupiter. Serpentine minerals are even found in meteorites, the fragments of embryonic planets that existed 4.5 billion years ago, just as Earth was being born—raising the possibility that the cradle of life’s origin actually existed before our planet did.
存在于阿曼的铁矿在整个太阳系都很常见，蛇纹石化的过程也是如此。目前环绕火星运行的太空探测器“勘测轨道飞行器”绘制了火星表面蛇纹石化矿物的分布地图。太空探测器卡西尼号在土星被冰覆盖的卫星土卫二深处发现了蛇纹石化的化学证据。在谷神星——一颗围绕太阳运行的矮行星，位于火星和木星之间——表面也发现了蛇纹石化矿物。蛇纹石化矿物甚至在陨石中也被发现了踪迹，而陨石则是45亿年前存在的行星胚胎的碎片，当时地球才刚刚诞生——这增加了生命起源的摇篮实际上比我们的星球更早存在的可能性。
Hydrogen—an energy source for nascent life—was produced in all of these places. It is probably still being produced throughout the solar system.
所有这些地方都产生了氢——一种生命初期的能源。它可能仍在整个太阳系的各处产生。
To Boyd, the implications are breathtaking.
对博伊德来说，其影响是惊人的。
“If you had rock like this, at a temperature similar to Earth, and you had liquid water, how inevitable do you think life is?” he asked. “My personal belief is, it’s inevitable.”
“如果你有像这样的岩石，温度和地球相似，还有液态水，你认为生命是不可避免的吗？”他问道，“我个人认为，这是不可避免的。”
Finding that life will be a challenge. With existing technologies, a probe sent to Mars could drill no more than a few feet below its hostile surface. Those shallow rocks might contain signs of past life—perhaps desiccated carcasses of Martian cells, sitting inside the microscopic tunnels that they chewed into the minerals—but any living microbes are likely to be buried hundreds of feet deeper. Templeton has grappled with the problem of detecting past signs of life—and of distinguishing those signs from things that happened without the influence of life—ever since she started looking at basaltic seafloor glasses 16 years ago.
发现这种生命将是一个挑战。根据现有技术，发射到火星的探测器只能钻探到其不友好的表面以下几英尺的地方。这些浅层岩石可能含有过去生命存在的迹象——也许是干燥的火星细胞尸体，躺在它们咀嚼矿物的显微隧道里——但是任何活着的微生物都可能被埋在更深的几百英尺的地方。自从16年前坦普尔顿开始研究玄武岩海底玻璃以来，她一直在努力解决探测过去的生命迹象的问题，以及如何将这些迹象与不受生命影响的事物区分开来。
“My job is to find bio-signatures,” she says. As she studies the rocks drilled out of Oman, she’ll subject them to some of the same tools that she used on the glasses. She will bounce X-rays off the mineral surface in order to map how the microbes are altering the minerals, and whether they are leaving metals in place or etching them away. By learning how living microbes chew on minerals, she hopes to find reliable ways of identifying those same chemical chew marks in extraterrestrial rocks that haven’t held living cells for thousands of years.
“我的工作是寻找生物的签名，”她说道。当她研究从阿曼钻出来的岩石时，她会使用一些她在眼镜上用过的工具来对付它们。她将从矿物表面反射X光，以绘制微生物如何改变矿物，以及它们是将金属留在原地还是蚀刻它们。通过研究活微生物如何咀嚼矿物质，她希望能找到可靠的方法来识别外星岩石中那些数千年来没有活细胞的化学咀嚼痕迹。
One day, these tools might be packed onto a Mars rover. Or they might be used on rocks that are brought back from other worlds. For now, she and her colleagues have plenty to do in Oman, figuring out what inhabits the dark, hot, hidden biosphere below their feet.
有一天，这些工具可能会被打包到火星探测器上。或者它们可能被用在从其他世界带回来的岩石上。目前，她和她的同事们在阿曼有很多事情要做，他们要弄清楚在他们脚下黑暗、炎热、隐秘的生物圈里栖息着什么。
