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Billions of years ago on the young planet Earth simple organic compounds assembled into more complex coalitions that could grow and reproduce.
几十亿年前，在年轻的地球上，简单的有机化合物形成了复杂的化合物，进而可以发育和繁衍。
They were the very first life on Earth, and they gave rise to every one of the billions of species that have inhabited our planet since.
它们是地球上出现的第一批生命，从那时起，这些生命逐渐进化出今天栖息在地球上的数十亿个物种。
At the time, Earth was almost completely devoid of what we'd recognize as a suitable environment for living things.
以今天的标准而言，彼时的地球环境几乎不适宜任何生物的生存。
The young planet had widespread volcanic activity and an atmosphere that created hostile conditions.
地球上布满了活火山，空气条件极其恶劣。
So where on Earth could life begin?
那么，生物是何时出现的呢？。
To begin the search for the cradle of life, it's important to first understand the basic necessities for any life form.
要想弄清生命的起源，就必须明白所有生命形式所必须的基本生存条件。
Elements and compounds essential to life include hydrogen, methane, nitrogen, carbon dioxide, phosphates, and ammonia.
它们是一些生命必不可少的元素和化合物，包括氢、甲烷、氮、二氧化碳、磷酸盐以及氨。
In order for these ingredients to comingle and react with each other, they need a liquid solvent: water.
为了混合这些物质，并使之发生化学反应，我们需要一种液体溶剂：水。
And in order to grow and reproduce, all life needs a source of energy.
为了进行发育繁衍，所有生命都需要能量源。
Life forms are divided into two camps: autotrophs, like plants, that generate their own energy,
生命形式分为两大类：一类为自养生物，例如植物，它们能自行产生能量，
and heterotrophs, like animals, that consume other organisms for energy.
另一类为异养生物，例如动物，它们通过消耗其他生物产生能量。
The first life form wouldn't have had other organisms to consume, of course,
当然，地球上出现的第一个生物没有其他生物可以消耗，
so it must have been an autotroph, generating energy either from the sun or from chemical gradients.
它必定是自养生物，依靠太阳能或化学梯度产生能量。
So what locations meet these criteria?
那么，哪里符合这样的标准呢？
Places on land or close to the surface of the ocean have the advantage of access to sunlight.
陆地和海洋表面有利于接受阳光。
But at the time when life began, the UV radiation on Earth's surface was likely too harsh for life to survive there.
然而在生命初始期，过强的紫外线辐射将威胁到生命的存活。
One setting offers protection from this radiation and an alternative energy source:
有一种场景，既能保护生命不受紫外线伤害又能提供替换的能量源：
the hydrothermal vents that wind across the ocean floor, covered by kilometers of seawater and bathed in complete darkness.
那就是遍布于海床上的海底热泉，覆盖于几千公里深的海水和伸手不见五指的漆黑之中。
A hydrothermal vent is a fissure in the Earth's crust where seawater seeps into magma chambers and is ejected back out at high temperatures,
海底热泉是由海水渗透进地壳表面产生的裂痕中，与滚烫的岩浆混合后，以极高的温度喷涌而出产生的，
along with a rich slurry of minerals and simple chemical compounds.
并带出丰富的矿物质和简单化合物。
Energy is particularly concentrated at the steep chemical gradients of hydrothermal vents.
在海底热泉陡峭的化学梯度中聚集着大量的能量。
There's another line of evidence that points to hydrothermal vents: the Last Universal Common Ancestor of life, or LUCA for short.
另一个证据也指向海底热泉：即最近普适共同祖先，简称LUCA。
LUCA wasn't the first life form, but it's as far back as we can trace.
这并非初始生命形式，而是人类能追溯到的生命最早形态。
Even so, we don't actually know what LUCA looked like -- there's no LUCA fossil, no modern-day LUCA still around
我们不知道它长什么样--也没人见过化石，更不存在活着的生物，
instead, scientists identified genes that are commonly found in species across all three domains of life that exist today.
实际上，科学家们从现存的三种生命形式的所有物种中找到了共存的基因。
Since these genes are shared across species and domains, they must have been inherited from a common ancestor.
也就是说，如果这些基因存在于所有物种和生命形式之中，那么它们必然继承于一个共同的祖先。
These shared genes tell us that LUCA lived in a hot, oxygen-free place and harvested energy from a chemical gradient -- like the ones at hydrothermal vents.
从这些基因可以得知，最后共同祖先生存在高温无氧的环境中，并从化学梯度中获取能量--海底热泉正好符合。
There are two kinds of hydrothermal vent: black smokers and white smokers.
海底热泉拥有两种形态：黑烟囱和白烟囱。
Black smokers release acidic, carbon-dioxide-rich water, heated to hundreds of degrees Celsius and packed with sulphur, iron, copper, and other metals essential to life.
黑烟囱释放出富含二氧化碳的酸性液体，温度可高达几百摄氏度，并含有大量的硫、铁、铜等生命必须的金属元素。
But scientists now believe that black smokers were too hot for LUCA
但科学家们认为黑烟囱温度过高，不利于LUCA存活，
so now the top candidates for the cradle of life are white smokers.
所以他们更倾向于白烟囱。
Among the white smokers, a field of hydrothermal vents on the Mid-Atlantic Ridge called Lost City has become the most favored candidate for the cradle of life.
而在所有白烟囱之中，位于大西洋中脊素有“失落之城”之称的那儿的一处海底热泉呼声最高。
The seawater expelled here is highly alkaline and lacks carbon dioxide, but is rich in methane and offers more hospitable temperatures.
这里的海水呈强碱性二氧化碳含量低，但甲烷含量高温度也更适合生存。
Adjacent black smokers may have contributed the carbon dioxide necessary for life to evolve at Lost City,
附近的黑烟囱可能贡献了必要的二氧化碳，使生命得以萌发并演化，
giving it all the components to support the first organisms that radiated into the incredible diversity of life on Earth today.
所有的元素汇集后，世界上第一个生物诞生了，并演变成如今地球上无与伦比的生物多样性。
