Breathing Easy Thanks To Great Oxidation Event

The earth’s original atmosphere would have been unpleasant—deadly in fact—to any organisms that breathe oxygen. There wasn’t any. Not until about 2.4 billion years ago anyway. That’s the time of what scientists call the Great Oxidation Event. Now researchers believe they’ve found clues as to what may have caused the change. They published their report in the April 9 edition of the journal Nature.

Researchers analyzed trace elements in sedimentary rock from dozens of sites. Turns out nickel was 400 times more abundant in primordial oceans than in today’s waters. Micro-organisms called methanogens love nickel-rich water, and they release methane into the atmosphere. Methane prevents a build-up of oxygen.

Scientists testing the rocks saw that around 2.7 to 2.4 billion years ago, ocean-dissolved nickel dropped off. This corresponds to the Great Oxidation Event. Lack of nickel could have killed off methanogens and left room for algae and other life forms that release oxygen during photosynthesis.

Researchers don’t know exactly why nickel decreased—possibly because of the cooling and solidifying of the earth’s mantle. But the nickel disappearance is one more clue about how the planet went from suffocating to a place where a terrestrial tetrapod could take a deep breath.

“大氧化事件”使我們能輕松呼吸

對(duì)于任何呼吸氧氣的有機(jī)體來(lái)說(shuō)，地球上原始的大氣很不舒適，而事實(shí)上這些大氣也是致命的，因?yàn)槟菚r(shí)候沒(méi)有任何氧氣存在，直到大約24億年前，氧氣才開(kāi)始出現(xiàn)。這個(gè)時(shí)間被科學(xué)家稱為“大氧化事件”。現(xiàn)在研究者們相信他們找到了導(dǎo)致這種變化的一些線索。研究者們?cè)?月9日的《自然》（Nature）雜志上發(fā)表了他們的研究結(jié)果。
 
研究者們分析了來(lái)自許多不同地方沉積巖中的痕量元素。結(jié)果發(fā)現(xiàn)在原始海洋中，鎳元素的含量是目前海洋中鎳元素含量的400多倍。名為產(chǎn)烷生物的微生物喜歡生活在富含鎳的水中，它們向空氣中釋放出甲烷。甲烷阻止了氧氣的逐步生成。
 
檢測(cè)了沉積巖后，科學(xué)家們發(fā)現(xiàn)大約在24億至27億年前，海洋中溶解的鎳大幅下降。這個(gè)時(shí)期和“大氧化事件”真好吻合。海洋中鎳的缺乏可能致使產(chǎn)烷生物的消亡，因此海藻以及其它形式的生物就可以利用光合作用釋放出氧氣。

研究者們還不能確切知道鎳的含量為什么會(huì)下降---這可能是由于地幔的冷卻以及固化所致。但是對(duì)于如何解釋我們的地球從一個(gè)令人窒息的環(huán)境轉(zhuǎn)變?yōu)橐粋�(gè)讓陸地四足動(dòng)物可以自由呼吸的地方，鎳的消失又提供了一個(gè)線索。
 
Vocabulary:

Oxidation: 氧化
Unpleasant: 令人不適的
Deadly: 致命地
Organism: 有機(jī)體；生物
Billion：十億
Clue: 線索；提示
Element: 化學(xué)元素
Sedimentary：沉積的
Abundant：大量的；豐富的
Primordial：原始的；早期的
Micro-organism：微生物
Methanogen：產(chǎn)烷生物
Nickel：鎳（一種化學(xué)元素，符號(hào)為Ni）
Dissolve：溶解
Algae: 海藻
Release: 釋放
Photosynthesis：光合作用
Solidify：固化
Mantle：地幔；斗篷
Suffocate: 窒息
Terrestrial: 陸地的；地球上的
Tetrapod: 四足類(lèi)動(dòng)物