英語聽力文摘 呼吸甲烷
A Fresh Breath of Methane
很早很早以前地球有很微量的氧氣，而且地表狀況十分惡劣。大氣主要是N2和Co2，后來通過復(fù)雜的變化，地球開始出現(xiàn)了厭氧型生物。在生命的作用下，地球的氧氣開始不斷積累。后來又出現(xiàn)了藻類，在各種(必須注意是各種)生物的作用下，氧氣開始積累。據(jù)科學(xué)家們說，甲烷生產(chǎn)可能是一系列導(dǎo)致形成可呼吸大氣的事件中一個(gè)被忽略了的環(huán)節(jié)。地球的早期環(huán)境中，氧氣是相當(dāng)稀薄的，甚至在光合作用的細(xì)菌出現(xiàn)后也是這樣。為了解釋這個(gè)滯后，David C. Catling和同事們提出這段時(shí)間的大部分可能被甲烷的生產(chǎn)所占據(jù)。根據(jù)這個(gè)假說，當(dāng)其它微生物分解有機(jī)物質(zhì)與可能的火山氣體時(shí)，光合生物產(chǎn)生的氫被轉(zhuǎn)化成甲烷。然后紫外線的轟擊將甲烷分解成二氧化碳、氧氣和氫氣。氫氣會(huì)逃逸到太空中，而重一些的氧氣將在大氣中積聚，使大氣日益適宜陸地的生命。
Y:Open the window and let some fresh air down.
D:Ok!
Y:A!Take a deep breath of oxygen.
D:It might not always been there,you know.
Y:What do you mean?
D:According to climate researcher James Kasting, when the earth first formed there might not have been any oxygen around.
Y:Before the begining of the life?
D:No,there would have been life, just no oxygen.For example, take methanogens, the microbes that make methane. They only thrive when there’s no oxygen around.
Y: Is that why they live in airless places like the stomachs of cows?
D: Correct!And according to the theory, back when the earth was young and there was no oxygen around, methanogens ruled and the atmosphere was filled with methane.
Y:So when did Oxygen come on the scene?
D:Not untill about a billion years later. But without methane, oxygen-producing microbes might not have evolved as quickly as they did. See, methane is a powerful greenhouse gas, meaning that it could have helped keep the sun’s rays trapped near the earth’s surface. This was important, since billions of years ago the sun was weaker than it is today. So without the methane-induced greenhouse effect, the earth might have frozen solid until the sun got hotter.
Y:But when the earth would have become way too hot?
D:Yes. If not for the fact that the methane rich atmosphere also could have helped to reflect enough incoming sunlight to maintain a delicate temperature balance.
Y:So maybe the earth stayed warm, but not too warm, until oxygen-producing microbes evolved and filled the atmosphere with oxygen, which drove away most of the methane.
D:Right.
Y:Well!You've just made my breath of fresh air more interesting.
譯文：
呼吸甲烷
Y：打開窗戶讓新鮮空氣進(jìn)來。
D：好的。
Y：啊!深吸一口氧氣。
D：你知道的，它不是一直都有的。
Y：什么意思?
D：氣候研究員的 James Kasting指出當(dāng)?shù)厍虺跏夹纬蓵r(shí)，周圍并沒有氧氣。
Y：在生命開始之前嗎?
D：不，有生命，只是沒有氧氣。比如產(chǎn)烷生物，一種制造甲烷的微生物。它們只在周圍沒有氧氣的時(shí)候才能生存。
Y：這就是它們?yōu)槭裁瓷钤谙衽Ｎ改菢硬煌L(fēng)的地方的原因嗎?
D：正確。根據(jù)理論，當(dāng)?shù)厍蚰贻p并且沒有氧氣的時(shí)候，產(chǎn)烷生物統(tǒng)治著地球，空氣里面充滿了甲烷。
Y：那么氧氣是什么時(shí)候出現(xiàn)的呢?
D: 直到大約十億年后。但是如果沒有甲烷，制氧微生物就不會(huì)進(jìn)化的如此之快。甲烷是一種強(qiáng)有力的溫室氣體，它可以維持地球表面的太陽光線。這是非常重要的。因?yàn)閹资畠|年前太陽的光線比現(xiàn)在弱。因此如果沒有甲烷制造的溫室效應(yīng)，地球可能會(huì)被凍成一個(gè)堅(jiān)硬的固體，直到陽光變強(qiáng)為止。
Y：但是地球變得太熱了怎么辦呢?
D：是的。甲烷豐富的大氣同樣有助于折射足夠多的射入陽光，使溫度保持一種微妙的平衡。
Y：所以地球保持著溫暖，但不至于太溫暖。直到制氧生物進(jìn)化完成，趕走了絕大多數(shù)的甲烷，讓大氣充滿氧氣。
D：是的。
Y: 嗯，你讓我呼吸新鮮空氣變得更有趣了。
