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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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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 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。由于泥炭是沼泽的产物,含水量很高,如不在容重数据中把水分这一因素剔除,则计算出的储量相当一部分吨位是由水分构成,而水分高低又受地表和地下水补给状况以及季节等因素所控制,因泥炭一般都埋深较浅,不少泥炭裸露地表,有的现在还在堆积发育。故计算泥炭储量时规定以干泥炭重量表示,否则储量真实性和可比性都将受到很大影响。 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。 一、GB474-83(下简称国标)对煤样的制备全过程未要求作碎样加工原始记录问题 碎样加工原始记录是重要原始资料之一。分析实验工作完毕送样单、碎样加工原始记录连同实验分析原始记录应装订成册、送审、抄发、归挡。以便对制样全过程中每个粒级原来重量和经过破碎、过筛、掺和、缩分引起煤样的重量变化以及加工损 相似文献
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Eutrophication and associated occurrence of hypoxic condition could cause significant damage to marine ecosystems, resulting in considerable economic losses to fisheries and aquaculture and is a major source of stress that fish often have to contend with in order to survive. This problem is likely to be exacerbated in the coming years, since the wastewater treatment facilities is unlikely to catch up with increasing human activities. Moreover, large-scale reclamation projects in coastal areas have recently been increased, and these activities certainly have adverse impacts on water quality and fisheries resources. Coastal construction has a significant role in the development of hypoxic water by changing the current and mixing pattern of water. Changes in species composition and decreases in species richness and diversity have been well documented in hypoxic systems. Hypoxia could cause endocrine disruption in fish and eliminate populations of sensitive species. Shallow coastal areas are of great importance for the special nursery of fish and shellfish and land reclamation in these areas cause strong damage to fisheries. Although the tolerance of aquatic life to hypoxia is known, there is no information about the mortality of fish caused by hypoxia because fish can swim around it and no modeling study has yet been carried out. Criteria that influence the movement of fish are: amounts of food, water temperature and depth, dissolved oxygen concentration and nature of seabed. However, among these, water temperature and dissolved oxygen are the most crucial parameters that affect survival, movement and growth of fish. In this paper, a model of fish preference and mortality for environmental conditions was developed and applied to the Hakata Bay where hypoxic water occurs every summer. For the purpose of this study, a field survey of fish behavior under hypoxic water was conducted by releasing marbled sale (Pleuronectes yokohamae) in the inner bay. Moreover, a series of preference tests for DO, salinity and temperature in the laboratory were conducted in order to decide preference parameters of fish. Using the results of both field and laboratory studies, a sub-module of fish preference and mortality was coded within an integrated hydrothermal and eutrophication model (CHEM) to predict the behavior and mortality of marbled sale when hypoxia would occur in the bay. The model could reasonably simulate the behavior of the fish under hypoxia. An assessment of the impact of the ongoing land reclamation project of about 401 ha in the Wajiro tidal flat zones at the head of the bay on the fisheries resources was also conducted using the model. The results showed that the artificial land lowered the mortality rate of fish under hypoxic condition in the bay during the summer period. 相似文献
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We report the direct observation of motion associated with a solar flare at a speed of 26,000 km s-1. The motion is seen from a radio source at 0.33 GHz, which suddenly starts moving during the flare. At its peak, the radio source covers a quiet region of dimension 500&arcsec;. Emission from any given location is sporadic. The disturbance itself does not seem to radiate, but it excites coronal features that continue to radiate after it passes. The inferred velocity is larger than any previously inferred velocity of a disturbance in the solar atmosphere apart from freely streaming beams of accelerated electrons. The observed motion of the source at a fixed frequency, low polarization, and moderate bandwidth are more consistent with the typical properties of moving type IV radio bursts than with classical coronal shock-associated type II bursts, but any disturbance at such a high velocity must be highly supersonic and should drive a shock. We speculate that the disturbance is associated with the realignment of magnetic fields connecting different portions of an active region. 相似文献