Scientists have found life in an ecosystem trapped underneath a glacier in Antarctica for nearly 2 million years. The microbes, they suggest, are surviving the dark, oxygen-free waters by drawing energy from sulfur and iron. The findings provide insight into how life may have survived "Snowball Earth" and hint at the possibility of life in other inhospitable environments, such as Mars and Jupiter's icy moon Europa.  

 在南極冰川下被封存了將近200萬年之久的一個(gè)生態(tài)系統(tǒng)中，科學(xué)家們發(fā)現(xiàn)了生命。他們提出，這些微生物通過硫和鐵來吸收能量，在黑暗和無氧的水域中生存下來。這些發(fā)現(xiàn)為科學(xué)家們提供了新的認(rèn)識(shí)，使他們了解到生命是如何度過“冰雪地球”時(shí)期的，同時(shí)也為他們提供了線索，表明在其他不可生存的環(huán)境中，如：在火星上以及被冰覆蓋的木星衛(wèi)星——木衛(wèi)二上，也有可能存在生命。

 Researchers have found microbial life surviving in the most unusual places: the depths of cold and dark oceans, seething geothermal vents, and the deepest layers of permafrost. And ever since scientists discovered Antarctica's dark and mysterious subglacial lakes in the late 1960s and early 1970s, they've wondered if microbes could make a life for themselves there too. But the challenges of drilling through kilometers of ice and concerns about contaminating these pristine lakes have curtailed previous efforts to find out.

 研究人員已經(jīng)發(fā)現(xiàn)微生物生存在最不同尋常的地方，如：寒冷黑暗的海洋深處，火熱的地?zé)岢隹谔?，以及永久凍結(jié)帶的最深層。自從科學(xué)家們?cè)诙兰o(jì)六十年代后期和七十年代初期發(fā)現(xiàn)了南極洲黑暗而神秘的冰下湖泊之后，他們一直想知道微生物是否也能夠獨(dú)自生存在那里。然而，由于鉆透厚厚的冰層所面臨的挑戰(zhàn)，以及擔(dān)心對(duì)這些原始湖泊會(huì)造成污染，以前尋找生命的努力受到限制。

 Blood Falls, a small, saltwater outflow from Taylor Glacier's subglacial lake in Antarctica's Dry Valleys, offers an alternative. The lake sits beneath 400 meters of ice and trickles out at the glacier's end, painting an orange stain across the ice as its iron-rich waters rust upon contact with air. The subglacial lake was originally part of a marine fjord system that became trapped as Taylor Glacier enclosed it between 1.5 million and 2 million years ago. Its sporadic outflow allows researchers to explore the lake without drilling or risking contamination of the isolated environment.

 南極干谷中泰勒冰川下面的湖泊流出細(xì)小的咸水流，被稱為“血色瀑布”，為研究人員提供了一個(gè)可以利用的研究方法。該湖泊位于冰面以下400米處，從冰川的末端流出，其富鐵的水質(zhì)遇到空氣后生銹，流經(jīng)冰面時(shí)染上一片橘紅色的痕跡。這個(gè)冰下湖泊起初是一個(gè)海洋峽灣系統(tǒng)的一部分，在150萬至200萬年以前，泰勒冰川將其封閉起來，一直被封存在冰下。湖水的偶爾外流使研究人員不用鉆探、不用冒險(xiǎn)污染這個(gè)隔離的環(huán)境，就可以進(jìn)行探索。

 Geomicrobiologist Jill Mikucki, now at Dartmouth College, collected water samples from Blood Falls over 6 years. A battery of tests revealed that its waters contained almost no oxygen and hosted a community of at least 17 different types of microorganisms. But how could they have survived for so long, with no light or oxygen? Mikucki and her team uncovered three main clues. First, a genetic analysis of the microbes showed that they were closely related to other microorganisms that use sulfate instead of oxygen for respiration. Second, isotopic analysis of sulfate's oxygen molecules revealed that the microbes were modifying sulfate in some form but not using it directly for respiration. Third, the water was enriched with soluble ferrous iron, which would happen only if the organisms had converted ferric iron, which is insoluble, to the soluble ferrous form. The best explanation, the team reports in tomorrow's issue of Science, is that the organisms use sulfate as a catalyst to "breathe" with ferric iron and metabolize the limited amounts of organic matter trapped with them years ago. Lab experiments have suggested this might be possible, but it has never been observed in a natural environment.

 目前供職于達(dá)特茅斯學(xué)院的地球微生物學(xué)家吉爾·米庫(kù)基在六年的時(shí)間里采集了血色瀑布的水樣。多次實(shí)驗(yàn)表明，水中幾乎沒有氧氣，卻擁有一個(gè)至少包含17種不同微生物的生態(tài)群落。然而，在沒有光線、沒有氧氣的情況下，它們何以存活了如此之久呢？米庫(kù)基及其研究小組發(fā)現(xiàn)了三個(gè)主要線索。首先，對(duì)這些微生物的遺傳分析表明，它們跟利用硫酸鹽而不用氧氣進(jìn)行呼吸的其他微生物密切相關(guān)；其次，對(duì)硫酸鹽中的氧分子所進(jìn)行的同位素分析顯示，這些微生物不斷地將某種形式的硫酸鹽進(jìn)行轉(zhuǎn)化，并沒有直接用來呼吸；第三，水中富含可溶解的亞鐵，只有當(dāng)這種微生物將不能溶解的三價(jià)鐵轉(zhuǎn)化為可溶于水的亞鐵形式時(shí)，才會(huì)發(fā)生這種情況。研究小組在明天出版的《科學(xué)》雜志中報(bào)道：最好的解釋是，這些微生物拿硫酸鹽作為一種催化劑，以便利用三價(jià)鐵進(jìn)行呼吸，代謝多年前封存于其中的少量有機(jī)質(zhì)。實(shí)驗(yàn)表明這種情況是有可能發(fā)生的，但是在自然環(huán)境中從未觀察到。

 "I think this is a fantastic study," says Alan Kaufman, a biogeochemist at the University of Maryland, College Park. It presents "a spectacular new environment that we can explore to understand life on the edge," he says. "A place like this ... would be probably as close of an analog as we can find on this planet for subpermafrost life habitats on Mars," says glaciologist Slawek Tulaczyk of the University of California, Santa Cruz. Ultraviolet radiation and other hazards would most likely lock life away beneath the surface of the Red Planet, he notes.

 “我認(rèn)為這是一項(xiàng)非常有意義的研究，”馬里蘭大學(xué)帕克分校的生物地球化學(xué)家艾倫·考夫曼說。他指出：“該研究展示出一個(gè)奇妙的新環(huán)境，我們可以通過探索這個(gè)環(huán)境來了解邊緣地帶的生命?！薄拔覀?cè)诘厍蛏纤l(fā)現(xiàn)的象這樣的地方很可能跟火星凍土以下的生命棲息地最為類似，”加州大學(xué)圣克魯茲分校的冰川學(xué)家斯拉維克·圖拉吉克說。他指出，紫外輻射和其他危害很可能將生命封鎖在那顆紅色行星的表面以下