The mysterious origins of life on Earth - Luka Seamus Wright

翻译人员: Meng Ren 校对人员: Lipeng Chen

Billions of years ago on the young planet Earth

几十亿年前，在年轻的地球上，

simple organic compounds assembled into more complex coalitions

简单的有机化合物 形成了复杂的化合物，

that could grow and reproduce.

进而可以发育和繁衍。

They were the very first life on Earth,

它们是地球上出现的第一批生命，

and they gave rise to every one of the billions of species

从那时起，这些生命逐渐进化出 今天栖息在地球上的

that have inhabited our planet since.

数十亿个物种。

At the time, Earth was almost completely devoid

以今天的标准而言， 彼时的地球环境

of what we’d recognize as a suitable environment for living things.

几乎不适宜任何生物的生存。

The young planet had widespread volcanic activity

地球上布满了活火山，

and an atmosphere that created hostile conditions.

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,

要想弄清生命的起源，

it’s important to first understand the basic necessities for any life form.

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,

它们是一些生命必不可少的 元素和化合物，

carbon dioxide, phosphates, and ammonia.

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,

为了混合这些物质， 并使之发生化学反应，

they need a liquid solvent: water.

我们需要一种液体溶剂：水。

And in order to grow and reproduce,

为了进行发育繁衍，

all life needs a source of energy.

所有生命都需要能量源。

Life forms are divided into two camps:

生命形式分为两大类：

autotrophs, like plants, that generate their own energy,

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,

它必定是自养生物，

generating energy either from the sun or from chemical gradients.

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

陆地和海洋表面

have the advantage of access to sunlight.

有利于接受阳光。

But at the time when life began, the UV radiation on Earth’s surface

然而在生命初始期， 过强的紫外线辐射

was likely too harsh for life to survive there.

将威胁到生命的存活。

One setting offers protection from this radiation

有一种场景，既能 保护生命不受紫外线伤害

and an alternative energy source:

又能提供替换的能量源：

the hydrothermal vents that wind across the ocean floor,

那就是遍布于海床上的海底热泉，

covered by kilometers of seawater and bathed in complete darkness.

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

海底热泉是由海水渗透进 地壳表面产生的裂痕中

where seawater seeps into magma chambers

与滚烫的岩浆混合后

and is ejected back out at high temperatures,

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

在海底热泉陡峭的化学梯度中

at the steep chemical gradients of hydrothermal vents.

聚集着大量的能量。

There’s another line of evidence that points to hydrothermal vents:

另一个证据也指向海底热泉：

the Last Universal Common Ancestor of life, or LUCA for short.

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—

我们不知道它长什么样——

there’s no LUCA fossil, no modern-day LUCA still around—

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

实际上，科学家们从现存的三种 生命形式的所有物种中

across all three domains of life that exist today.

找到了共存的基因。

Since these genes are shared across species and domains,

也就是说，如果这些基因存在于 所有物种和生命形式之中，

they must have been inherited from a common ancestor.

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

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，

and harvested energy from a chemical gradient—

并从化学梯度中获取能量——

like the ones at hydrothermal vents.

海底热泉正好符合。

There are two kinds of hydrothermal vent:

海底热泉拥有两种形态：

black smokers and white smokers.

黑烟囱和白烟囱。

Black smokers release acidic, carbon-dioxide-rich water,

黑烟囱释放出富含 二氧化碳的酸性液体，

heated to hundreds of degrees Celsius and packed with sulphur, iron, copper,

温度可高达几百摄氏度 并含有大量的硫、铁、铜等

and other metals essential to life.

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,

而在所有白烟囱之中，

a field of hydrothermal vents on the Mid-Atlantic Ridge called Lost City

位于大西洋中脊 素有“失落之城”之称的

has become the most favored candidate for the cradle of life.

那儿的一处海底热泉呼声最高。

The seawater expelled here is highly alkaline and lacks carbon dioxide,

这里的海水呈强碱性 二氧化碳含量低，

but is rich in methane and offers more hospitable temperatures.

但甲烷含量高 温度也更适合生存。

Adjacent black smokers may have contributed the carbon dioxide necessary

附近的黑烟囱可能贡献了 必要的二氧化碳，

for life to evolve at Lost City,

使生命得以萌发并演化，

giving it all the components to support the first organisms

所有的元素汇集后， 世界上第一个生物诞生了，

that radiated into the incredible diversity of life on Earth today.

并演变成如今地球上 无与伦比的生物多样性。