一個(gè)國(guó)際研究小組稱,，來自澳大利亞皮爾巴拉帶狀含鐵巖層的鐵礦石核心樣本將大氣中氧氣首次出現(xiàn)的時(shí)間追溯到了24.8億年前,。
帶領(lǐng)這個(gè)研究小組的馬克·巴利教授說，他們的發(fā)現(xiàn)基于巖石樣本的可靠性,。這項(xiàng)研究發(fā)表在《自然》雜志上,。
地理學(xué)家稱，大氧化事件發(fā)生在24.8億年前至23.2億年前,，地球大氣中的氧氣就是在那個(gè)時(shí)期形成的,。
巴利教授說：“這證明了有氧呼吸生命的最初形態(tài)有氧呼吸細(xì)菌氧化了黃鐵礦，產(chǎn)生出溶解巖石和土壤的酸,，然后被水流帶到海洋里,。”
“有氧呼吸細(xì)菌需要與藍(lán)細(xì)菌共生產(chǎn)生氧氣才能實(shí)現(xiàn)這一過程，”巴利教授說,，地理生物學(xué)家正在建立更完善的數(shù)據(jù)庫,，為這種與氧氣含量提高有關(guān)的細(xì)菌到底何時(shí)發(fā)生作用尋找更多證據(jù)。
他說：“我們從帶狀含鐵巖層中找到了大量樣本,，分析了鉻同位素和其他元素,，因?yàn)槟强梢蕴峁┭趸钣辛Φ淖C據(jù)。”（生物谷Bioon.com）
doi:10.1038/nature10511
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PMID:
Aerobic bacterial pyrite oxidation and acid rock drainage during the Great Oxidation Event
Kurt O. Konhauser, Stefan V. Lalonde, Noah J. Planavsky, Ernesto Pecoits, Timothy W. Lyons, Stephen J. Mojzsis, Olivier J. Rouxel, Mark E. Barley, Carlos Rosìere, Phillip W. Fralick, Lee R. Kump & Andrey Bekker
The enrichment of redox-sensitive trace metals in ancient marine sedimentary rocks has been used to determine the timing of the oxidation of the Earth’s land surface1, 2. Chromium (Cr) is among the emerging proxies for tracking the effects of atmospheric oxygenation on continental weathering; this is because its supply to the oceans is dominated by terrestrial processes that can be recorded in the Cr isotope composition of Precambrian iron formations3. However, the factors controlling past and present seawater Cr isotope composition are poorly understood. Here we provide an independent and complementary record of marine Cr supply, in the form of Cr concentrations and authigenic enrichment in iron-rich sedimentary rocks. Our data suggest that Cr was largely immobile on land until around 2.48 Gyr ago, but within the 160 Myr that followed—and synchronous with independent evidence for oxygenation associated with the Great Oxidation Event (see, for example, refs 4–6)—marked excursions in Cr content and Cr/Ti ratios indicate that Cr was solubilized at a scale unrivalled in history. As Cr isotope fractionations at that time were muted, Cr must have been mobilized predominantly in reduced, Cr(III), form. We demonstrate that only the oxidation of an abundant and previously stable crustal pyrite reservoir by aerobic-respiring, chemolithoautotrophic bacteria could have generated the degree of acidity required to solubilize Cr(III) from ultramafic source rocks and residual soils7. This profound shift in weathering regimes beginning at 2.48 Gyr ago constitutes the earliest known geochemical evidence for acidophilic aerobes and the resulting acid rock drainage, and accounts for independent evidence of an increased supply of dissolved sulphate8 and sulphide-hosted trace elements to the oceans around that time1, 9. Our model adds to amassing evidence that the Archaean-Palaeoproterozoic boundary was marked by a substantial shift in terrestrial geochemistry and biology.
