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Preservation of biological information in thermal spring deposits: developing a strategy for the search for fossil life on Mars 总被引:1,自引:0,他引:1
Current interpretations of the early history of Mars suggest many similarities with the early Earth and therefore raise the possibility that the Archean and Proterozoic history of life on Earth could have a counterpart on Mars. Terrestrial experience suggests that, with techniques that can be employed remotely, ancient springs, including thermal springs, could well yield important information. By delivering water and various dissolved species to the sunlit surface of Mars, springs very likely created an environment suitable for life, which could have been difficult, if not impossible, to attain elsewhere. The chemical and temperature gradients associated with thermal springs sort organisms into sharply delineated, distinctive and different communities, and so diverse organisms are concentrated into relatively small areas in a predictable and informative fashion. A wide range of metabolic strategies are concentrated into small areas, thus furnishing a useful and representative sampling of the existing biota. Mineral-charged springwaters frequently deposit chemical precipitates of silica and/or carbonate which incorporate microorganisms and preserve them as fossils. The juxtaposition of stream valley headwaters with volcanoes and impact craters on Mars strongly implies that subsurface heating of groundwater created thermal springs. On Earth, thermal springs create distinctive geomorphic features and chemical signatures which can be detected by remote sensing. Spring deposits can be quite different chemically from adjacent rocks. Individual springs can be hundreds of meters wide, and complexes of springs occupy areas up to several kilometers wide. Benthic microbial mats and the resultant stromatolites occupy a large fraction of the available area. The relatively high densities of fossils and microbial mat fabrics within these deposits make them highly prospective in any search for morphological evidence of life, and there are examples of microbial fossils in spring deposits as old as 300 Myr. 相似文献
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Franco JL Posser T Mattos JJ Sánchez-Chardi A Trevisan R Oliveira CS Carvalho PS Leal RB Marques MR Bainy AC Dafre AL 《Marine environmental research》2008,66(1):88-89
The aim of this study was to investigate biochemical changes in juvenile carp (Cyprinus carpio) exposed to zinc chloride (10, 30 and 100 microM) for a period of 48 h. Zinc exposure caused a concentration-dependent reduction in glutathione reductase (GR) activity in gills, liver and brain. Gill glutathione S-transferase (GST) was reduced when animals were exposed to the highest concentration of 100 microM zinc. The phosphorylation of p38(MAPK) increased in the brain of fish exposed to zinc 100 microM, while phosphorylation of the extracellular signal-regulated protein kinase 1/2 (ERK1/2) and c-Jun N-terminal protein kinase 1/2 (JNK1/2) remained unchanged. Expression of proteins HSP60 and HSP70 were not affected by zinc exposure. Considering the significant concentration-dependent inhibition of GR in all tissues analyzed, this enzyme could be a potential biomarker of exposure to zinc, which has to be confirmed. 相似文献
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泥炭的容重是指在天然赋存条件下,包括存在于泥炭中的孔隙、裂隙、缝隙时的重量和同温度、同体积水重之比叫容重,或称假比重、视比重。在野外用刻槽法测出的比重又叫“体重”。容重的大小受泥炭内部所含泥沙、分解度、植物残体组成和外用的复盖层厚度、采样到测试时间长短、送来样品是否保持原状泥炭等内外因素所制约。通过容重测定可了解泥炭的结构和矿物杂质大致含量,容重是泥炭地质普查勘探计算储量时的必要数据之一。 相似文献
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煤样的制备是煤质分析十分重要的一个环节,要求通过煤样制备取得具有代表性的实验样品,当然也要求流程合理,在保证样品具有代表性的同时保证有一定的工作效率,最近颁发要求在1984年5月实施的国家标准GB474-83《煤样的制备方法》在这方面起了促进作用,但我们认为尚有某些不足和值得进一步研讨地方,现提出以下商榷意见,以便在集思广益的基础上,使之臻于完善。 相似文献
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长期以来地质矿产部没有开展泥炭资源的地质普查勘探工作,国务院[1979]200号文件下达后,推动了我国泥炭地质工作的发展。为了进一步搞好我国的泥炭地质工作,国家经委于1982年决定,今后将有关泥炭资源的普查、勘探和管理工作划归地质矿产部来领导和组织进行。 相似文献
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