Identifying bio-interaction with basaltic glass in oceanic crust and implications for estimating the depth of the oceanic biosphere: A review
Published:January 01, 2002
H. Furnes, I. H. Thorseth, T. Torsvik, K. Muehlenbachs, H. Staudigel, O. Tumyr, 2002. "Identifying bio-interaction with basaltic glass in oceanic crust and implications for estimating the depth of the oceanic biosphere: A review", Volcano–Ice Interaction on Earth and Mars, J. L. Smellie, M. G. Chapman
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The alteration of basaltic glass in the volcanic part of the oceanic crust is, to a substantial extent, biologically mediated. Evidence of microbial interaction with basaltic glass can be provided by a number of independent observations, such as: (1) Textures at the alteration front, generated by dissolution of the glass and subsequent precipitation. These bio-generated textures can be defined as a granular type (dominant) and a tubular type, and show size and form which are compatible with microbial etching. (2) Filament-like structures, representing organic remains, appear in connection with bio-generated textures. (3) Within areas of the bio-generated textures, particularly at the alteration front, DNA and ribosomal RNA have been demonstrated to be present in relatively young samples. (4) X-ray mapping shows that carbon and nitrogen invariably appear within the bio-generated textures, in young samples most strongly enriched at the alteration front. (5) Carbon isotopes (δ13C) in carbonates extracted from the glassy margin of pillows show highly variable values which can be explained in terms of bio-fractionation of the 12C and 13C isotopes. Estimates of the proportion of bio-genetic alteration products of basaltic glass, on the basis of textural relationships, suggest that bio-alteration is dominant compared to abiotic alteration in the upper 300 m of the oceanic crust, and declines to become insignificant at a depth of about 500 m.
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Volcano–Ice Interaction on Earth and Mars
This volume focuses on magmas and cryospheres on Earth and Mars and is the first publication of its kind to combine a thematic set of contributions addressing the diverse range of volcano-ice interactions known or thought to occur on both planets. Understanding those interactions is a comparatively young scientific endeavour, yet it is vitally important for a fuller comprehension of how planets work as integrated systems. It is also topical since future volcanic eruptions on Earth may contribute to melting ice sheets and thus to global sea level rise.
Papers included here are likely to influence the choice of sites for future Mars missions in exobiologically important areas. On Earth, snow and ice are widespread, not only in extensive icecaps but also as alpine glaciers at high elevations in tropical regions. By contrast, Mars today is an arid volcanic planet with only small polar ice-caps although an abundance of water is believed to be trapped in the cryolithosphere. It is also thought that the planet may have sustained extensive frozen oceans early in its history. The presence of a former hydrosphere, a cryosphere and coincident volcanism thus make Mars the likeliest prospect for the first discoveries of life away from Earth. Much research has assumed that terrestrial volcano-ice systems are plausible analogues for putative Martian examples, but until mankind finally sets foot on Mars, there is no simple test for that assumption.
Our hope is that the knowledge presented here will stimulate research among planetary geologists in this exciting, rapidly expanding field for many years to come.