The mysterious origins of life on Earth - Luka Seamus Wright

譯者: Lilian Chiu 審譯者: Bruce Sung

Billions of years ago on the young planet Earth

數十億年前，在年輕的地球上，

simple organic compounds assembled into more complex coalitions

簡單的有機化合物組合 成了更複雜的結合體，

that could grow and reproduce.

能夠成長及繁殖。

They were the very first life on Earth,

它們是地球上最早的生命，

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

自此之後，地球上 出現的數十億種物種

that have inhabited our planet since.

通通都起源於它們。

At the time, Earth was almost completely devoid

在當時，地球上可說是非常缺乏

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

我們認為適合生物的環境。

The young planet had widespread volcanic activity

在年輕的地球上， 到處都是火山活動，

and an atmosphere that created hostile conditions.

當時的大氣也造成了 很不友善的條件。

So where on Earth could life begin?

所以，生命究竟起源於 地球上的何處？

To begin the search for the cradle of life,

若要開始尋找生命的搖籃，

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

很重要的是先要了解

各種生命形式有什麼基本需求。

Elements and compounds essential to life include hydrogen, methane, nitrogen,

對生命來說必備的元素 和化合物包括：氫、甲烷、

carbon dioxide, phosphates, and ammonia.

氮、二氧化碳、磷酸鹽、氨。

In order for these ingredients to comingle and react with each other,

若這些要素彼此之間 要能混合、產生作用，

they need a liquid solvent: water.

就需要有液體的溶媒：水。

And in order to grow and reproduce,

若要成長和繁殖，

all life needs a source of energy.

所有生命都需要能量來源。

Life forms are divided into two camps:

生命形式可以分成兩大類：

autotrophs, like plants, that generate their own energy,

自營生物，如植物， 會產生自己要用的能量，

and heterotrophs, like animals, that consume other organisms for energy.

以及異營生物，如動物， 要食用其他有機體來取得能量。

The first life form wouldn’t have had other organisms to consume, of course,

當然，最早的生命形式 不會有其他有機體可以食用，

so it must have been an autotroph,

所以它們一定是自營生物，

generating energy either from the sun or from chemical gradients.

能量來自太陽或化學梯度。

So what locations meet these criteria?

所以，什麼地點能符合這些條件？

Places on land or close to the surface of the ocean

地面上的地方，或海洋中 接近表面的地方

have the advantage of access to sunlight.

比較有取得陽光的優勢。

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

但在生命剛出現時， 地球表面上的紫外線

was likely too harsh for life to survive there.

很可能太過嚴酷， 讓生命無法存活下來。

One setting offers protection from this radiation

有一種環境能提供 保護，阻擋紫外線，

and an alternative energy source:

同時也有替代的能量來源：

the hydrothermal vents that wind across the ocean floor,

在海底蜿延的海底熱泉區，

covered by kilometers of seawater and bathed in complete darkness.

它們被數公里的海水覆蓋， 完全處在黑暗中。

A hydrothermal vent is a fissure in the Earth’s crust

深海熱泉區是地球地殼上的裂縫，

where seawater seeps into magma chambers

在那裡，海水會滲入岩漿庫中，

and is ejected back out at high temperatures,

接著以高溫重新被噴射出來，

along with a rich slurry of minerals and simple chemical compounds.

附帶的泥漿中豐含 礦物質及簡單的化合物。

Energy is particularly concentrated

深海熱泉區的陡峭化學梯度

at the steep chemical gradients of hydrothermal vents.

有特別集中的能量。

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

還有其他證據證明 深海熱泉區是生命起源：

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

生命的最後共同祖先（LUCA）。

LUCA wasn’t the first life form, but it’s as far back as we can trace.

LUCA 並非最早的生命形式， 但它已古早到我們無法追蹤。

Even so, we don’t actually know what LUCA looked like—

即便如此，我們其實不知道 LUCA 是什麼樣子的——

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

沒有 LUCA 化石， 也沒有現代 LCUA 存在——

instead, scientists identified genes that are commonly found in species

不過，科學家發現，

在現今仍然存在的 三大生命領域物種中

across all three domains of life that exist today.

有些共同的基因存在。

Since these genes are shared across species and domains,

因為這些基因存在於 不同的物種和領域，

they must have been inherited from a common ancestor.

它們一定是來自共同的祖先。

These shared genes tell us that LUCA lived in a hot, oxygen-free place

這些共同基因告訴我們 LUCA 住在一個很熱、沒有氧氣的地方，

and harvested energy from a chemical gradient—

並從化學梯度取得能量——

like the ones at hydrothermal vents.

就像深海熱泉區的化學梯度。

There are two kinds of hydrothermal vent:

有兩種深海熱泉區：

black smokers and white smokers.

黑煙囪和白煙囪。

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

黑煙囪會釋放富含 二氧化碳的酸性水，

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

溫度高達攝氏數百度，

且滿是硫磺、鐵、銅，

and other metals essential to life.

以及其他對生命很重要的金屬。

But scientists now believe that black smokers were too hot for LUCA—

但現在科學家相信， 對 LUCA 而言黑煙囪太熱了——

so now the top candidates for the cradle of life are white smokers.

所以，最可能是生命搖籃的 候選地點是白煙囪。

Among the white smokers,

在各處的白煙囪當中，

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

在大西洋中洋脊有一塊 深海熱泉區叫做失落城市，

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

是最有可能的生命搖籃候選地點。

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

這裡噴出的海水是高度鹼性的， 且缺乏二氧化碳，

but is rich in methane and offers more hospitable temperatures.

但富含甲烷，溫度也比較適宜。

Adjacent black smokers may have contributed the carbon dioxide necessary

鄰近的黑煙囪可能有提供 失落城市的生命在演化時

for life to evolve at Lost City,

所必需要的二氧化碳，

giving it all the components to support the first organisms

補全了支持最早有機體 所必要的所有元素，

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

這些有機體才能發散出去， 形成現今地球上多樣化的生命。