Roughly 3 billion years ago,
大约30亿年前，
a single-celled photosynthetic bacterium began burping a new chemical that was poisonous to nearly every species on Earth.
一种单细胞光合细菌开始吐出一种新化学物质，这种化学物质对地球上几乎所有物种都有毒。
Over the following hundreds of millions of years, more microorganisms began producing this toxic gas,
在接下来的数亿年里，更多的微生物开始产生这种有毒气体，
first saturating Earth's oceans and eventually its atmosphere.
首先充满了地球的海洋，最终充满了大气。
Up here, this chemical changed the composition of pre-existing gases so drastically that it caused a global ice age.
在这里，这种化学物质极大地改变了现有气体的成分，导致了全球冰河时代。
And the name of this powerful, poisonous, world-changing gas?
这种强大、有毒、改变世界的气体的名字是什么？
Oxygen.
氧气
In the millions of years since the Great Oxygen Catastrophe, most life, including all multicellular organisms, have evolved to rely on this gas.
自氧气大灾难以来的数百万年里，大多数生命，包括所有多细胞生物，都进化到依赖这种气体。
However, there are some places where oxygen-averse microorganisms, like those from Earth's earliest days, have re-emerged.
然而，在某些地方，厌恶氧气的微生物（例如地球最早时期的微生物）已经重新出现。
Many of these places are in the ocean depths, beyond the reach of researchers.
其中许多地方位于海洋深处，研究人员无法到达。
But there are other bodies of water completely devoid of oxygen, yet close enough to the surface to explore.
但还有其他水域完全缺氧，但距离地表足够近，可以探索。
And one such lake is hidden high in the Swiss Alps' Piora Valley.
其中一个湖泊隐藏在瑞士阿尔卑斯山的皮奥拉山谷中。
Formed over 10,000 years ago, Lake Cadagno is one of roughly 200 known meromictic lakes,
卡达尼奥湖形成于一万多年前，是大约200个已知的分裂湖之一，
meaning it's actually two distinct bodies of water stacked on top of each other.
这意味着它实际上是两个相互堆叠的不同水体。
The top layer functions like a standard body of freshwater.
顶层的就像标准的淡水体。
It's safe for swimming and known mostly for a plump and plentiful fish population that's been the subject of local fishing legends for centuries.
它适合游泳，并以其丰满而丰富的鱼类种群而闻名，几个世纪以来一直是当地渔业传奇的主题。
But just 13 meters beneath that bounty is a dense, sulfurous, oxygen-free pool lethal to any multicellular life forms, fish included.
但在这片土地下方仅13米处，有一个浓密的、含硫的、无氧的水池，对包括鱼类在内的任何多细胞生命形式都是致命的。
In a typical lake, the entire body of water would gradually mix, diffusing oxygen from the surface throughout.
在典型的湖泊中，整个水体会逐渐混合，将氧气从表面扩散到各处。
But these two layers never mix, as is the case with any meromictic lake.
但这两层永远不会混合，就像任何分裂湖的情况一样。
And the reason for this divide in Cadagno is the waters' unique chemical compositions.
卡达尼奥出现这种分歧的原因是水域独特的化学成分。
Both layers are fed by rainwater flowing down the mountains, however, this water can take two paths.
这两层都由从山上流下的雨水供水，然而，这些水可以通过两条路径。
The first is to trickle down the granitic mountain directly into the top layer.
第一种是沿着花岗岩山直接滴流到顶层。
The second is to seep into the Piora Valley's vein of dolomite— a porous rock full of salts such as sulfate.
第二种是渗入皮奥拉山谷的白云岩脉--一种充满硫酸盐等盐类的多孔岩石。
Rainwater that sinks into the dolomite will slowly inch towards the lake, all the while shedding its oxygen and picking up salts.
沉入白云岩中的雨水会慢慢地流向湖水，同时释放氧气并吸收盐分。
Finally, this heavier water will cascade from sublacustrine springs below the lake's surface, forming the dense, salt-rich bottom layer.
最后，这些较重的水将从湖面以下的湖底泉水中倾泻而下，形成致密、富含盐分的底层。
This lower layer is anoxic, meaning oxygen free, and will suffocate any oxygen-dependent life.
这个下层是无氧的，这意味着没有氧气，并且会窒息任何依赖氧气的生命。
But it's ideal for the kind of anaerobic bacteria that died off in the Great Oxygen Catastrophe.
但它对于在大氧灾难中死亡的那种厌气细菌来说是理想的选择。
The flow from the sublacustrine springs creates microenvironments which feed large aggregates of microorganisms that emerge from the lakebed in strange and otherworldly shapes.
来自湖底泉水的水流创造了微环境，为大量微生物提供养分，这些微生物以奇怪和超凡脱俗的形状从湖底出现。
Various anaerobic microorganisms take in the water's sulfate and emit toxic sulfide.
各种厌氧微生物吸收水中的硫酸盐并释放有毒的硫。
And at the border of these layers, there's a thin blanket mainly composed of pink-bodied Chromatium okenii:
在这些层的边缘，有一层主要由粉红色体奥肯氏染色菌组成的薄薄的毯子：
a photosynthesizing bacterium that relies on this sulfur the way most plants rely on oxygen.
一种光合细菌，依赖这种硫，就像大多数植物依赖氧气一样。
However, while neither water nor organisms move between the layers, these ecosystems aren't completely out of touch.
然而，虽然水和生物体都不会在层之间移动，但这些生态系统并非完全脱节。
Chromatium okenii live at the top of the bottom layer because they need to be as close to the sun as possible.
奥肯染色菌生活在底层的顶部，因为它们需要尽可能靠近太阳。
But while they never cross into the deadly oxygenated waters, they're close enough that organisms like zooplankton can dive down, eat them,
但是，虽然它们永远不会进入致命的含氧水域，但它们距离足够近，浮游动物等生物可以潜入水中吃掉它们，
and get back up.
然后再回来。
In fact, this relationship forms the bottom of the upper layer's robust food chain supporting the lake's legendary fish population.
事实上，这种关系形成了上层强大食物链的底部，支撑着湖泊传奇的鱼类种群。
This unique ecology is more than just a boon for Cadagno's fishermen.
这种独特的生态不仅仅是卡达尼奥渔民的福音。
Having access to an isolated anaerobic ecosystem allows scientists to model the world before the Great Oxygen Catastrophe.
通过接触隔离的无氧生态系统，科学家们可以对大氧灾难之前的世界进行建模。
For example, when Chromatium okenii form their blanket, they increase the density of that thin layer of water.
例如，当okenii染色菌形成毯子时，它们会增加薄薄一层水的密度。
As the water sinks, these microorganisms are forced to swim back up, creating a minute mixing of water called bio- convection.
随着水下沉，这些微生物被迫游回，产生一种称为生物对流的微小水混合。
This billions of years old phenomenon might be a clue to how early life evolved the ability to swim.
这种已有数十亿年历史的现象可能是早期生命如何进化出游泳能力的线索。
And it's just one of the many insights that await researchers studying Cadagno's mysterious depths.
这只是研究人员研究卡达尼奥神秘深处的众多见解之一。
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