地球上最早的生命和外星生命可能都是紫色的

一項最新研究稱，地球上最早的生物體可能呈薰衣草般的淡紫色。在綠色植物開始利用陽光獲取能量之前，這些紫色的微生物早就開始進行光合作用了。研究人員還指出，外星生命也可能採用這種生存機制。所以，除了在太空中探測綠色生命，科學家也許還需將目光轉向紫色的外星生命。

Alien life might be purple.

外星生命也許是紫色的。

That's the conclusion of a new research paper that suggests that the first life on Earth might have had a lavender hue. In the International Journal of Astrobiology, microbiologist Shiladitya DasSarma of the University of Maryland School of Medicine and postdoctoral researcher Edward Schwieterman at the University of California, Riverside, argue that before green plants started harnessing the power of the sun for energy, tiny purple organisms figured out a way to do the same.

這是一篇新研究論文的結論。這篇論文指出，地球上最早的生命可能擁有薰衣草的顏色。馬里蘭大學醫學院微生物學家希拉迪蒂亞·達斯薩爾馬和加利福尼亞大學裏弗賽德分校博士後研究員愛德華·施維特曼在《國際天體生物學雜誌》上發表論文指出，在綠色植物開始吸收太陽光以獲取能量之前，微小的紫色生物體就已經在這麼做了。

hue [hjuː] : n.色彩；色度；色調

Alien life could be thriving in the same way, DasSarma said.

達斯薩爾馬說，外星生命可能會以同樣的方式茁壯成長。

"Astronomers have discovered thousands of new extrasolar planets recently and are developing the capacity to see surface biosignatures" in the light reflected from these planets, he told Live Science. There are already ways to detect green life from space, he said, but scientists might need to start looking for purple, too.

他告訴趣味科學網站說，“天文學家最近發現了數千顆新的太陽系外行星，並且正在開發從這些行星反射出的光線中觀察表面生物特徵的能力”。他說，科學家已經有辦法探測太空中的綠色生命，但或許他們還需要開始尋找紫色的生命。

紫色的地球

The idea that the early Earth was purple is not new, DasSarma and his colleagues advanced the theory in 2007. The thinking goes like this: Plants and photosynthesizing algae use chlorophyll to absorb energy from the sun, but they don't absorb green light. That's odd, because green light is energy-rich. Perhaps, DasSarma and his colleagues reasoned, something else was already using that part of the spectrum when chlorophyll photosynthesizers evolved.

關於早期地球是紫色的設想並不新鮮，達斯薩爾馬和他的同事們在2007年就提出了這一假設。這種想法是這樣的：植物和進行光合作用的藻類利用葉綠素吸收來自太陽的能量，但它們並不吸收綠光。這很奇怪，因爲綠光富含能量。達斯薩爾馬和他的同事們推斷，也許，在葉綠素光合作用生物進化出現的時候，某種使用那部分光譜的其他生物體已經存在了。

chlorophyll ['klɔːrəfɪl; 'klɒ-]: n.葉綠素

That "something else" would be simple organisms that captured solar energy with a molecule called retinal. Retinal pigments absorb green light best. They're not as efficient as chlorophylls in capturing solar energy, but they are simpler, the researchers wrote in their new paper.

這種“其他生物體”可能是通過一種被稱爲視黃醛的分子捕獲太陽能量的簡單生物體。視黃醛色素能夠最大程度地吸收綠光。研究人員在新發表的論文中寫道，視黃醛色素在獲取太陽能量時的效率不如葉綠素，但它們更爲簡單。

Retinal light-harvesting is still widespread today among bacteria and the single-celled organisms called Archaea. These purple organisms have been discovered everywhere from the oceans to the Antarctic Dry Valley to the surfaces of leaves, Schwieterman told Live Science. Retinal pigments are also found in the visual system of more complex animals.

以視黃醛採集光能的方式今天在細菌和被稱爲“古細菌”的單細胞生物體中仍然十分普遍。施維特曼告訴美國趣味科學網站說，從海洋到南極洲幹谷再到植物葉子表面，到處都發現過這種紫色生物體。視黃醛色素也存在於較爲複雜的動物視覺系統中。

The appearance of the pigments across many living organisms hints that they may have evolved very early on, in ancestors common to many branches of the tree of life, the researchers wrote. There is even some evidence that modern purple-pigmented salt-loving organisms called halophiles might be related to some of the earliest life on Earth, which thrived around methane vents in the ocean, Schwieterman said.

研究人員寫道，這些色素在衆多生物有機體中的出現，暗示它們可能在很早的時候就在生命之樹衆多分支所共有的祖先體內完成了進化。施維特曼說，甚至有一些證據表明，被稱爲“嗜鹽菌”的現代紫色喜鹽微生物可能與地球上某些最早的生命形式有關，這些生命曾經在海洋中的甲烷噴口附近旺盛生長。

紫色的外星人

Regardless of whether the first life on Earth was purple, it's clear that lavender life suits some organisms just fine, Schwieterman and DasSarma argue in their new paper. That means that alien life could be using the same strategy. And if alien life is using retinal pigments to capture energy, astrobiologists will find them only by looking for particular light signatures, they wrote.

施維特曼和達斯薩爾馬在他們的新論文中指出，不管地球上最早的生命是否呈紫色，顯然薰衣草色的生命十分適合某些有機體。這意味着外星生命可能在使用同樣的方式。他們寫道，如果外星生命正在利用視黃醛色素捕獲能量，那麼天體生物學家將只有通過尋找特定的光線標記才能找到它們。

Chlorophyll, Schwieterman said, absorbs mostly red and blue light. But the spectrum reflected from a plant-covered planet displays what astrobiologists call a "vegetation red edge." This "red edge" is a sudden change in the reflection of light at the near-infrared part of the spectrum, where plants suddenly stop absorbing red wavelengths and start reflecting them away.

施維特曼說，葉綠素主要吸收紅光和藍光。但從一顆覆蓋着植物的行星上反射過來的光譜將顯示天體生物學家所說的“植被紅邊”。這種“紅邊”是光譜中接近紅外區域的光線反射的突然變化，植物會突然停止吸收位於該區域的紅色波長光並開始將它們反射出去。

spectrum ['spektrəm] : n.光譜；頻譜

Retinal-based photosynthesizers, on the other hand, have a "green edge," Schwieterman said. They absorb light up to the green portion of the spectrum, and then start reflecting longer wavelengths away.

施維特曼說，另一方面，基於視黃醛的光合生物體擁有“綠邊”。它們吸收光譜中綠色區域以下的光線，然後開始反射波長更長的光。

Astrobiologists have long been intrigued by the possibility of detecting extraterrestrial life by detecting the "red edge," Schwieterman said, but they may need to consider searching for the "green edge," too.

施維特曼說，天體生物學家長期以來一直癡迷於通過探測“紅邊”來發現外星生命的可能性，但或許他們也需要考慮尋找“綠邊”。

"If these organisms were present in sufficient densities on an exoplanet, those reflection properties would be imprinted on that planet's reflected light spectrum," he said.

他說：“如果這些生物體以足夠的密度存在於某個外星行星上，那麼這些反射特性就會記錄在該行星的反射光譜上。”