據(jù)2月20日的《科學(xué)》雜志報道說,，在一個有25億年歷史的澳大利亞頁巖中所測到的氮和碳同位素也許可以捕捉到現(xiàn)代需氧氮素循環(huán)的最初日子,，該循環(huán)是由遠(yuǎn)古的微生物活動所驅(qū)動的。
這個氮素循環(huán)的中心是微生物,，這一化學(xué)旅程將氮素從其大氣形式轉(zhuǎn)變?yōu)樗猩w所使用的形式,。Jessica Garvin及其同僚檢驗(yàn)了這些同位素的證據(jù)后提出，現(xiàn)代的氮素循環(huán)（即在此循環(huán)中,，能加工氧的細(xì)菌幫助產(chǎn)生了硝酸鹽和亞硝酸鹽,。）可能在氧氣于23億年前開始積累之前就已經(jīng)形成了。這些發(fā)現(xiàn)提示,，至少有一個主要的氮素加工細(xì)菌組在地球的大氣變得富含氧氣之前就已經(jīng)演化而成了,。（生物谷Bioon.com）
生物谷推薦原始出處：
Science 20 February 2009:DOI: 10.1126/science.1165675
Isotopic Evidence for an Aerobic Nitrogen Cycle in the Latest Archean
Jessica Garvin,1 Roger Buick,1* Ariel D. Anbar,2,3 Gail L. Arnold,2 Alan J. Kaufman4
The nitrogen cycle provides essential nutrients to the biosphere, but its antiquity in modern form is unclear. In a drill core though homogeneous organic-rich shale in the 2.5-billion-year-old Mount McRae Shale, Australia, nitrogen isotope values vary from +1.0 to +7.5 per mil () and back to +2.5 over 30 meters. These changes evidently record a transient departure from a largely anaerobic to an aerobic nitrogen cycle complete with nitrification and denitrification. Complementary molybdenum abundance and sulfur isotopic values suggest that nitrification occurred in response to a small increase in surface-ocean oxygenation. These data imply that nitrifying and denitrifying microbes had already evolved by the late Archean and were present before oxygen first began to accumulate in the atmosphere.
1 Department of Earth and Space Sciences and Astrobiology Program, University of Washington, Seattle, WA 98195–1310, USA.
2 School of Earth and Space Exploration, Arizona State University, Tempe, AZ85287, USA.
3 Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287, USA.
4 Department of Geology, University of Maryland, College Park, MD20742, USA.
