地球上最早的生命和外星生命可能都是紫色的

一项最新研究称，地球上最早的生物体可能呈薰衣草般的淡紫色。在绿色植物开始利用阳光获取能量之前，这些紫色的微生物早就开始进行光合作用了。研究人员还指出，外星生命也可能采用这种生存机制。所以，除了在太空中探测绿色生命，科学家也许还需将目光转向紫色的外星生命。

 Alien life might be purple.

外星生命也许是紫色的。

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.

这是一篇新研究论文的结论。这篇论文指出，地球上最早的生命可能拥有薰衣草的颜色。马里兰大学医学院微生物学家希拉迪蒂亚·达斯萨尔马和加利福尼亚大学里弗赛德分校博士后研究员爱德华·施维特曼在《国际天体生物学杂志》上发表论文指出，在绿色植物开始吸收太阳光以获取能量之前，微小的紫色生物体就已经在这么做了。

hue [hjuː] : n.色彩；色度；色调

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

达斯萨尔马说，外星生命可能会以同样的方式茁壮成长。

"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.

他告诉趣味科学网站说，“天文学家最近发现了数千颗新的太阳系外行星，并且正在开发从这些行星反射出的光线中观察表面生物特征的能力”。他说，科学家已经有办法探测太空中的绿色生命，但或许他们还需要开始寻找紫色的生命。

 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.

关于早期地球是紫色的设想并不新鲜，达斯萨尔马和他的同事们在2007年就提出了这一假设。这种想法是这样的：植物和进行光合作用的藻类利用叶绿素吸收来自太阳的能量，但它们并不吸收绿光。这很奇怪，因为绿光富含能量。达斯萨尔马和他的同事们推断，也许，在叶绿素光合作用生物进化出现的时候，某种使用那部分光谱的其他生物体已经存在了。

chlorophyll  ['klɔːrəfɪl; 'klɒ-]: n.叶绿素

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.

这种“其他生物体”可能是通过一种被称为视黄醛的分子捕获太阳能量的简单生物体。视黄醛色素能够最大程度地吸收绿光。研究人员在新发表的论文中写道，视黄醛色素在获取太阳能量时的效率不如叶绿素，但它们更为简单。

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.

以视黄醛采集光能的方式今天在细菌和被称为“古细菌”的单细胞生物体中仍然十分普遍。施维特曼告诉美国趣味科学网站说，从海洋到南极洲干谷再到植物叶子表面，到处都发现过这种紫色生物体。视黄醛色素也存在于较为复杂的动物视觉系统中。

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.

研究人员写道，这些色素在众多生物有机体中的出现，暗示它们可能在很早的时候就在生命之树众多分支所共有的祖先体内完成了进化。施维特曼说，甚至有一些证据表明，被称为“嗜盐菌”的现代紫色喜盐微生物可能与地球上某些最早的生命形式有关，这些生命曾经在海洋中的甲烷喷口附近旺盛生长。

 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.

施维特曼和达斯萨尔马在他们的新论文中指出，不管地球上最早的生命是否呈紫色，显然薰衣草色的生命十分适合某些有机体。这意味着外星生命可能在使用同样的方式。他们写道，如果外星生命正在利用视黄醛色素捕获能量，那么天体生物学家将只有通过寻找特定的光线标记才能找到它们。

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.

施维特曼说，叶绿素主要吸收红光和蓝光。但从一颗覆盖着植物的行星上反射过来的光谱将显示天体生物学家所说的“植被红边”。这种“红边”是光谱中接近红外区域的光线反射的突然变化，植物会突然停止吸收位于该区域的红色波长光并开始将它们反射出去。

spectrum ['spektrəm] : n.光谱；频谱

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.

施维特曼说，另一方面，基于视黄醛的光合生物体拥有“绿边”。它们吸收光谱中绿色区域以下的光线，然后开始反射波长更长的光。

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.

施维特曼说，天体生物学家长期以来一直痴迷于通过探测“红边”来发现外星生命的可能性，但或许他们也需要考虑寻找“绿边”。

"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.

他说：“如果这些生物体以足够的密度存在于某个外星行星上，那么这些反射特性就会记录在该行星的反射光谱上。”