据2月20日的《科学》杂志报道说，在一个有25亿年历史的澳大利亚页岩中所测到的氮和碳同位素也许可以捕捉到现代需氧氮素循环的最初日子，该循环是由远古的微生物活动所驱动的。
这个氮素循环的中心是微生物，这一化学旅程将氮素从其大气形式转变为所有生命体所使用的形式。Jessica Garvin及其同僚检验了这些同位素的证据后提出，现代的氮素循环（即在此循环中，能加工氧的细菌帮助产生了硝酸盐和亚硝酸盐。）可能在氧气于23亿年前开始积累之前就已经形成了。这些发现提示，至少有一个主要的氮素加工细菌组在地球的大气变得富含氧气之前就已经演化而成了。（生物谷Bioon.com）
生物谷推荐原始出处：
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.
