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这种单细胞生物是如何消灭了几乎整个地球生物的 – 译学馆
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这种单细胞生物是如何消灭了几乎整个地球生物的

How a single-celled organism almost wiped out life on Earth - Anusuya Willis

这是一个改变了世界的生物
There’s an organism that changed the world.
它导致了地球历史上第一次大规模的灭绝
It caused both the first mass extinction in Earth’s history
但也为之后的复杂生命铺平了道路
and also paved the way for complex life.
怎么做到的呢?
How?
它们把第一个自由氧分子送到我们的大气层中并且
By sending the first free oxygen molecules into our atmosphere,
它们是以单细胞的生命形态来完成这一切的
and they did all this as single-celled life forms.
它们就是蓝藻
They’re cyanobacteria,
这些简单的生物
and the story of these simple organisms
没有细胞核和其它任何细胞器而它们的故事
that don’t even have nuclei or any other organelles
正是地球上生命的故事的一个关键章节
is a pivotal chapter in the story of life on Earth.
地球的大气层并非一直充满着我们现在呼吸的富氧的混合物
Earth’s atmosphere wasn’t always the oxygen-rich mixture we breathe today.
3.5亿年以前 大气层中的大多是氮气
3.5 billion years ago, the atmosphere was mostly nitrogen,
二氧化碳
carbon dioxide,
和甲烷
and methane.
几乎所有的氧气都被锁在像水一样的分子里
Almost all oxygen was locked up in molecules like water,
并不是在空气中飘着
not floating around in the air.
海洋被厌氧微生物填充
The oceans were populated by anaerobic microbes.
它们是在没有氧气的环境中茁壮成长的 以单细胞形式存在的简单生物
Those are simple, unicellular life forms that thrive without oxygen
它们从它们找到的被净化的分子中汲取能力
and get energy by scavenging what molecules they find.
但在2.5到3.5亿年前
But somewhere between 2.5 and 3.5 billion years ago,
这类微生物群中的一个
one of these microbial species,
可能正飘在海洋表面
probably floating on the surface of the ocean,
进化出了一种新的能力:
evolved a new ability: photosynthesis.
光合作用它们细胞膜中的结构可以利用阳光中的能量
Structures in their cell membrane could harness the energy from sunlight
将二氧化碳和水转化成氧气和糖分
to turn carbon dioxide and water into oxygen gas and sugars,
并作为它们的能源
which they could use for energy.
这些生物就是我们现在说的蓝藻的祖先
Those organisms were the ancestors of what we now call cyanobacteria.
它们的蓝色来源于蓝绿色素
Their bluish color comes from the blue-green pigments
可用于捕捉它们所需要的阳光
that capture the sunlight they need.
光合作用使这些古老的细菌比别的物种有更大的优势
Photosynthesis gave those ancient bacteria a huge advantage over other species.
它们可以从基本上无尽的原材料中
They could now produce their own energy
生产它们自己的能源
from an almost endless supply of raw ingredients,
所以它们的数量剧增
so their populations exploded
并开始向大气中排出一种新型废弃物:
and they started polluting the atmosphere with a new waste product: oxygen.
氧气一开始 流出的额外的氧气在和铁的化学反应
At first, the trickle of extra oxygen was soaked up by chemical reactions with iron
或细胞分解中被吸收了
or decomposing cells,
但在数百万年之后
but after a few hundred million years,
蓝藻生产氧气的速度比它们吸收的要快
the cyanobacteria were producing oxygen faster than it could be absorbed,
气体开始在大气层中聚集
and the gas started building up in the atmosphere.
这对地球上的其它生物来说是个大问题事实上
That was a big problem for the rest of Earth’s inhabitants.
富氧的空气对它们来说是有毒的结果
Oxygen-rich air was actually toxic to them.
呢?
The result?
2.5亿年前是一个地球上所有生命的大灭绝
About 2.5 billion years ago was a mass extinction of virtually all life on Earth,
但几乎没有影响到蓝藻
which barely spared the cyanobacteria.
地质学家吧这个叫做大氧化事件
Geologists call this the Great Oxygenation Event,
甚至氧气大灾难
or even the Oxygen Catastrophe.
这不是仅有的问题
That wasn’t the only problem.
甲烷一直是使地球温暖的强效温室气体但现在
Methane had been acting as a potent greenhouse gas that kept the Earth warm,
多余的氧气和甲烷反应产生二氧化碳和水
but now, the extra oxygen reacted with methane to form carbon dioxide and water,
而不会留住热量
which don’t trap as much heat.
越来越薄的大气层
The thinner atmospheric blanket
导致了地球上第一次 也可能是最长的一次冰期
caused Earth’s first, and possibly longest, ice age,
休伦冰期
the Huronian Glaciation.
星球基本上是一个大雪球
The planet was basically one giant snowball
并持续了数亿年最终
for several hundred million years.
生命适应了
Eventually, life adjusted.
需氧生物 可以将氧气作为能源
Aerobic organisms, which can use oxygen for energy,
开始吸收大气中一些多余的气体
started sopping up some of the excess gas in the atmosphere.
氧气的浓度又上又下
The oxygen concentration rose and fell
直到最终达到了我们今天的浓度也就是大约21%
until eventually it reached the approximate 21% we have today.
可以利用氧气中的化学能量
And being able to use the chemical energy in oxygen
给了这些生物它们需要的刺激来实现多元化
gave organisms the boost they needed to diversify
并进化出更复杂的形态
and evolve more complex forms.
蓝藻在这一段故事中也有一个角色
Cyanobacteria had a part to play in that story, too.
几亿年前
Hundreds of millions of years ago,
其它一些史前微生物吞噬了蓝藻
some other prehistoric microbe swallowed a cyanobacterium whole
这整个过程称为内共生
in a process called endosymbiosis.
为了这样做 那个微生物必须拥有自己的内部光合作用工厂
In doing so, that microbe acquired its own internal photosynthesis factory.
这就是植物细胞的祖先
This was the ancestor of plant cells.
蓝藻变成了叶绿体
And cyanobacteria became chloroplasts,
就是今天那个可以光合作用的细胞器
the organelles that carry out photosynthesis today.
蓝藻还在地球上的几乎每一个环境:
Cyanobacteria are still around in almost every environment on Earth:
海洋
oceans,
淡水
fresh water,
土地南极石
soil,
树懒
antarctic rocks,

sloth fur.
它们依然在向大气中泵出氧气
They still pump oxygen into the atmosphere,
它们也依然将氮气析出 以给它们创造的植物施肥
and they also pull nitrogen out to fertilize the plants they helped create.
如果不是它们 我们不会认识到生命
We wouldn’t recognize life on Earth without them.
但也要谢谢它们
But also thanks to them,
地球上差点就没有生命了
we almost didn’t have life on Earth at all.

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