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The role of microbes in accretion, lamination and early lithification of modern marine stromatolites 总被引:28,自引:0,他引:28
Reid RP Visscher PT Decho AW Stolz JF Bebout BM Dupraz C Macintyre IG Paerl HW Pinckney JL Prufert-Bebout L Steppe TF DesMarais DJ 《Nature》2000,406(6799):989-992
For three billion years, before the Cambrian diversification of life, laminated carbonate build-ups called stromatolites were widespread in shallow marine seas. These ancient structures are generally thought to be microbial in origin and potentially preserve evidence of the Earth's earliest biosphere. Despite their evolutionary significance, little is known about stromatolite formation, especially the relative roles of microbial and environmental factors in stromatolite accretion. Here we show that growth of modern marine stromatolites represents a dynamic balance between sedimentation and intermittent lithification of cyanobacterial mats. Periods of rapid sediment accretion, during which stromatolite surfaces are dominated by pioneer communities of gliding filamentous cyanobacteria, alternate with hiatal intervals. These discontinuities in sedimentation are characterized by development of surface films of exopolymer and subsequent heterotrophic bacterial decomposition, forming thin crusts of microcrystalline carbonate. During prolonged hiatal periods, climax communities develop, which include endolithic coccoid cyanobacteria. These coccoids modify the sediment, forming thicker lithified laminae. Preservation of lithified layers at depth creates millimetre-scale lamination. This simple model of modern marine stromatolite growth may be applicable to ancient stromatolites. 相似文献
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Blood respiratory properties of a viviparous amphibian. 总被引:1,自引:0,他引:1
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The presence of transforming growth factor activity in early chick embryos was directly demonstrated by the ability of limb and tail buds to induce anchorage independent division in NRK 49 f cells. Colony number increased with limb bud number and developmental stage. Medium conditioned by tail buds contained some stimulating effect, and strongly promoted the action of other transforming growth factors. 相似文献
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J. C. McLachlan J. Macintyre D. D. Hume J. Smith 《Cellular and molecular life sciences : CMLS》1988,44(4):351-352
Summary The presence of transforming growth factor activity in early chick embryos was directly demonstrated by the ability of limb and tail buds to induce anchorage independent division in NRK 49f cells. Colony number increased with limb bud number and developmental stage. Medium conditioned by tail buds contained some stimulating effect, and strongly promoted the action of other transforming growth factors. 相似文献
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