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  • There's an organism that changed the world.

    有個生物群體存在改變了全世界的樣貌

  • It caused both the first mass extinction in Earth's history

    它不僅造成了地球史上第一次大規模生物滅絕

  • and also paved the way for complex life.

    也替複雜生命形式的出現鋪造了一條康莊大道

  • How?

    它究竟是怎麼辦到的?

  • By sending the first free oxygen molecules into our atmosphere,

    憑藉它們以單細胞生物的生命之姿

  • and they did all this as single-celled life forms.

    將第一批自由的氧氣分子輸送進入我們的大氣層中

  • They're cyanobacteria,

    它們是藍菌

  • and the story of these simple organisms

    這些簡單到

  • that don't even have nuclei or any other organelles

    連細胞核或其他的胞器都沒有的生物體的故事

  • is a pivotal chapter in the story of life on Earth.

    卻寫下了地球生物史上舉足輕重的一章

  • Earth's atmosphere wasn't always the oxygen-rich mixture we breathe today.

    地球的大氣層並不如我們現今所見地一直是充滿著我們所呼吸的氧氣

  • 3.5 billion years ago, the atmosphere was mostly nitrogen,

    35億年前,大氣其實充滿著氮氣

  • carbon dioxide,

    二氧化碳

  • and methane.

    以及甲烷

  • Almost all oxygen was locked up in molecules like water,

    幾乎全部的氧氣都被鎖在像是水那樣的分子裡頭

  • not floating around in the air.

    並不是漂浮在空氣中的

  • The oceans were populated by anaerobic microbes.

    海洋裡充斥著不需要氧氣就能夠生存的微生物群

  • Those are simple, unicellular life forms that thrive without oxygen

    這些簡單的單核生物形式在無氧的環境中勃發

  • and get energy by scavenging what molecules they find.

    且從它們尋得的腐敗分子當中獲取能量

  • But somewhere between 2.5 and 3.5 billion years ago,

    但約在25億至35億年前

  • one of these microbial species,

    其中的一個微生物物種中

  • probably floating on the surface of the ocean,

    或許它們生長的環境是漂浮在海洋的表面處

  • evolved a new ability: photosynthesis.

    演化出一種新的能力:光合作用

  • Structures in their cell membrane could harness the energy from sunlight

    它們細胞膜的結構使他們能夠從日光中採集能量

  • to turn carbon dioxide and water into oxygen gas and sugars,

    將二氧化碳和水轉換成氧氣以及糖分

  • which they could use for energy.

    作為能量的來源

  • Those organisms were the ancestors of what we now call cyanobacteria.

    這些生物體都是我們現在稱為藍菌這種細菌的祖先

  • Their bluish color comes from the blue-green pigments

    它們身上的藍色來自於藍-綠色素

  • that capture the sunlight they need.

    也就是它們用來採集陽光的工具

  • Photosynthesis gave those ancient bacteria a huge advantage over other species.

    光合作用能力使得這些細菌祖先們比其他物種要來得佔有優勢

  • They could now produce their own energy

    它們因此能夠從幾近永無止境的原料當中

  • from an almost endless supply of raw ingredients,

    獨門生產它們自己所需的能源

  • so their populations exploded

    也因此導致了它們數量大爆發

  • and they started polluting the atmosphere with a new waste product: oxygen.

    且它們生產能源產出的廢物,也就是氧氣,已經開始污染大氣

  • At first, the trickle of extra oxygen was soaked up by chemical reactions with iron

    一開始,為數不多的多餘氧氣被鐵元素

  • or decomposing cells,

    或者自然界中扮演生物分解角色的細胞的化學反應給吸收

  • but after a few hundred million years,

    但過了幾個百萬年之後

  • the cyanobacteria were producing oxygen faster than it could be absorbed,

    藍菌們所製造的氧氣速度已經高過了可以被吸收的速度

  • and the gas started building up in the atmosphere.

    這些多餘的氣體開始在大氣中堆積起來

  • That was a big problem for the rest of Earth's inhabitants.

    對於地球上其他的居住者來說是個很大的問題

  • Oxygen-rich air was actually toxic to them.

    充斥著氧氣的空氣對它們來說其實有毒性

  • The result?

    結果呢?

  • About 2.5 billion years ago was a mass extinction of virtually all life on Earth,

    在25億年前左右就造成了一場地球上生物的大滅絕

  • which barely spared the cyanobacteria.

    幾乎就只剩下藍菌存活下來

  • Geologists call this the Great Oxygenation Event,

    地理學家稱之為大氧化事件

  • or even the Oxygen Catastrophe.

    或者甚至氧氣浩劫

  • That wasn't the only problem.

    這並不是唯一的問題

  • Methane had been acting as a potent greenhouse gas that kept the Earth warm,

    甲烷是維持地球溫暖的一種溫室氣體

  • but now, the extra oxygen reacted with methane to form carbon dioxide and water,

    但現在,額外的氧氣與甲烷反應形成了二氧化碳雨水

  • which don't trap as much heat.

    能夠留在地球上的熱量就減少了

  • The thinner atmospheric blanket

    這個越來越薄的大氣

  • caused Earth's first, and possibly longest, ice age,

    讓地球經歷了第一次,也許是持續最久的,冰河時期

  • the Huronian Glaciation.

    休倫冰河時期

  • The blanket was basically one giant snowball

    地球基本上就是一個巨大的雪球

  • for several hundred million years.

    持續了好幾百萬年的時間

  • Eventually, life adjusted.

    最終,生物調適了

  • Aerobic organisms, which can use oxygen for energy,

    好氧性生物體,也就是能夠利用氧氣當做能量來源的生物

  • started sopping up some of the excess gas in the atmosphere.

    開始將大氣中過多的氧氣分解掉

  • The oxygen concentration rose and fell

    氧氣濃度起起伏伏

  • until eventually it reached the approximate 21% we have today.

    直到最終達到今天約21%氧氣佔大氣的濃度為止

  • And being able to use the chemical energy in oxygen

    且開始能夠使用氧氣中的化學能

  • gave organisms the boost they needed to diversify

    讓生物體得以產生多樣性

  • and evolve more complex forms.

    並演化至更複雜的形式

  • Cyanobacteria had a part to play in that story, too.

    藍菌也在這個故事中佔有一席之地

  • Hundreds of millions of years ago,

    幾億年前

  • some other prehistoric microbe swallowed a cyanobacterium whole

    一些其他的史前微生物將藍菌整個吞入

  • in a process called endosymbiosis.

    經歷一個我們現在稱為內共生的過程

  • In doing so, that microbe acquired its own internal photosynthesis factory.

    如此一來,這個微生物體就獲得了它自己的內部光合作用工廠

  • This was the ancestor of plant cells.

    也就是植物細胞的祖先

  • And cyanobacteria became chloroplasts,

    而藍菌變成了所謂的葉綠體

  • the organelles that carry out photosynthesis today.

    在今日植物細胞中進行光合作用的胞器

  • Cyanobacteria are still around in almost every environment on Earth:

    藍菌仍生活在地球的各個角落:

  • oceans,

    海洋中

  • fresh water,

    淡水中

  • soil,

    土地裡

  • antarctic rocks,

    南極圈岩石中

  • sloth fur.

    樹懶得毛髮中

  • They still pump oxygen into the atmosphere,

    它們仍在將氧氣注入大氣中

  • and they also pull nitrogen out to fertilize the plants they helped create.

    且也將氮從空氣中取出以對它們協助催生的植物們提供養分

  • We wouldn't recognize life on Earth without them.

    如果沒有它們我們幾乎不可能在地球上找到生物

  • But also thanks to them,

    但也多虧了它們

  • we almost didn't have life on Earth at all.

    地球過去幾乎沒有任何生物存活下來

There's an organism that changed the world.

有個生物群體存在改變了全世界的樣貌

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B2 中高級 中文 美國腔 TED-Ed 氧氣 生物 地球 大氣 光合作用

TED-Ed】一個單細胞生物體是如何幾乎消滅地球上的生命的--阿努蘇亞-威利斯。 (【TED-Ed】How a single-celled organism almost wiped out life on Earth - Anusuya Willis)

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    a0903021988 發佈於 2021 年 01 月 14 日
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