Distinguishing biological from hydrothermal signatures via sulphur and carbon isotopes in Archaean mineralizations at 3.8 and 2.7 Ga
N. V. Grassineau, P. W. U. Appel, C. M. R. Fowler, E. G. Nisbet, 2005. "Distinguishing biological from hydrothermal signatures via sulphur and carbon isotopes in Archaean mineralizations at 3.8 and 2.7 Ga", Mineral Deposits and Earth Evolution, I. McDonald, A. J. Boyce, I. B. Butler, R. J. Herrington, D. A. Polya
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Carbon and sulphur isotopes have been analysed in mineralization from two Archaean greenstone belts at 3.8 Ga and 2.7 Ga, with the aim of distinguishing between the inorganic and organic processes that occurred. Despite an obvious overprinting by metamorphism (in the early belt), or hydrothermal fluids, there are convincing differences between the values of carbon and sulphur in inorganic formations and those formed by biological processes. An attempt is made to estimate the changes that occurred in the early life activities over this 1 Ga year period. Life in the Isua Greenstone Belt (3.8 Ga) was most likely present in transitory settings, probably under high temperature conditions. This was very different from the life at 2.7 Ga in the Belingwe Greenstone Belt, indicated by ranges of 38‰ for δ34S and 37‰ for δ13Cred. By this time, the biological sulphur and carbon cycles seem to have reached almost full operation, with the presence of well-established photosynthetic microbial mat communities.
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Mineral Deposits and Earth Evolution
Mineral deposits are not only primary sources of wealth generation, but also act as windows through which to view the evolution and interrelationships of the Earth system.
Deposits formed throughout the last 3.8 billion years of the Earth’s history preserve key evidence with which to test fundamental questions about the evolution of the Earth. These include: the nature of early magmatic and tectonic processes, supercontinent reconstructions, the state of the atmosphere and hydrosphere with time, and the emergence and development of life. The interlinking processes that form mineral deposits have always sat at the heart of the Earth system and the potential for using deposits as tools to understand that evolving system over geological time is increasingly recognized. This volume contains research aimed both at understanding the origins of mineral deposits and at using mineral deposits as tools to explore different long-term Earth processes.