Biomarker evidence for green and purple sulphur bacteria in a stratified Palaeoproterozoic sea
Biomarker evidence for green and purple sulphur bacteria in a stratified Palaeoproterozoic sea
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DOI：
10.1038/nature04068
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发表时间：
2005-10-06
期刊：
影响因子：
64.8
通讯作者：
Bowden, SA
中科院分区：
文献类型：
--
作者：
Brocks, JJ;Love, GD;Bowden, SA
地质记录中类似于18亿年前（Gyr）的铁结构的消失是2.45 - 2.32 Gyr前大气中氧含量上升的结果（1-3）。它标志着由缺氧和富含铁的深海主导的2.5 gyr时期的结束。然而，尽管在大陆风化过程中，由于硫化物氧化作用的增强，氧含量上升，海洋硫酸盐浓度也随之增加(4)，但在随后的中元古代时期（类似于1.8 - 0.8 Gyr以前），海洋的化学成分可能还不像我们现代富氧的海洋。最近的数据（5-8）表明，在这一时期，海洋氧和硫酸盐浓度可能一直远低于目前的水平，有一种模式表明，缺氧和含硫的海洋盆地分布广泛，甚至可能在全球分布(4)。本文通过对澳大利亚北部1.64 gyr -old盆地的油气生物标志物（分子化石）研究，揭示了中元古代海洋群落的生态结构。生物标志表明该海相盆地具有缺氧、含硫、贫硫酸盐和永久分层的深水，对真核藻类不利。根据新的类胡萝卜素生物标志物okenane，在地质记录中发现了光养紫色硫细菌（Chromatiaceae），它们似乎与绿硫细菌（Chlorobiaceae）群落共存。总的来说，这些生物标记物支持了越来越多的证据，证明一个长期存在的元古代世界的氧气水平远低于现代水平。
The disappearance of iron formations from the geological record similar to 1.8 billion years (Gyr) ago was the consequence of rising oxygen levels in the atmosphere starting 2.45 - 2.32 Gyr ago(1-3). It marks the end of a 2.5-Gyr period dominated by anoxic and iron-rich deep oceans. However, despite rising oxygen levels and a concomitant increase in marine sulphate concentration, related to enhanced sulphide oxidation during continental weathering(4), the chemistry of the oceans in the following mid-Proterozoic interval (similar to 1.8 - 0.8 Gyr ago) probably did not yet resemble our oxygen-rich modern oceans. Recent data(5-8) indicate that marine oxygen and sulphate concentrations may have remained well below current levels during this period, with one model indicating that anoxic and sulphidic marine basins were widespread, and perhaps even globally distributed(4). Here we present hydrocarbon biomarkers ( molecular fossils) from a 1.64-Gyr-old basin in northern Australia, revealing the ecological structure of mid-Proterozoic marine communities. The biomarkers signify a marine basin with anoxic, sulphidic, sulphate-poor and permanently stratified deep waters, hostile to eukaryotic algae. Phototrophic purple sulphur bacteria ( Chromatiaceae) were detected in the geological record based on the new carotenoid biomarker okenane, and they seem to have co-existed with communities of green sulphur bacteria ( Chlorobiaceae). Collectively, the biomarkers support mounting evidence for a long-lasting Proterozoic world in which oxygen levels remained well below modern levels.