外星生命可能是紫色的

Alien life might be purple.

That’s the conclusion of a new research paper that suggests 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.

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

“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.

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.

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.

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.

Words to Learn 相关词汇

【淡紫色的】dànzǐsè de

lavender of a pale bluish-purple

【叶绿素】yèlǜsù

chlorophyll a green pigment that captures light energy used as the energy source in photosynthesis

外星生命也许是紫色的。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。

达斯萨尔马说，外星生命可能会以同样的方式茁壮成长。

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。

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。

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。

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。

(Chinadaily.com.cn)