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| Titel |
Geodynamic and metabolic cycles in the Hadean |
| VerfasserIn |
M. J. Russell, N. T. Arndt |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 2, no. 1 ; Nr. 2, no. 1 (2005-04-05), S.97-111 |
| Datensatznummer |
250000382
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| Publikation (Nr.) |
 copernicus.org/bg-2-97-2005.pdf |
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| Zusammenfassung |
| High-degree melting of hot dry Hadean mantle at ocean ridges and plumes resulted in
a crust about 30km thick, overlain in places by extensive and thick mafic volcanic
plateaus. Continental crust, by contrast, was relatively thin and mostly submarine. At
constructive and destructive plate boundaries, and above the many mantle plumes,
acidic hydrothermal springs at ~400°C contributed Fe and other transition elements as
well as P and H2 to the deep ocean made acidulous by dissolved CO2 and minor HCl
derived from volcanoes. Away from ocean ridges, submarine hydrothermal fluids
were cool (≤100°C), alkaline (pH ~10), highly reduced and also H2-rich. Reaction of
solvents in this fluid with those in ocean water was catalyzed in a hydrothermal
mound, a natural self-restoring flow reactor and fractionation column developed
above the alkaline spring. The mound consisted of brucite, Mg-rich clays, ephemeral
carbonates, Fe-Ni sulfide and green rust. Acetate and glycine were the main products,
some of which were eluted to the ocean. The rest, along with other organic byproducts
were retained and concentrated within Fe-Ni sulfide compartments. These
compartments, comprising the natural hydrothermal reactor, consisted partly of
greigite (Fe5NiS8). It was from reactions between organic modules confined within
these inorganic compartments that the first prokaryotic organism evolved. These
acetogenic precursors to the bacteria diversified and migrated down the mound and
into the ocean floor to inaugurate the "deep biosphere". Once there they were
protected from cataclysmic heating events caused by large meteoritic impacts.
Geodynamic forces led to the eventual obduction of the deep biosphere into the photic
zone where, initially protected by a thin veneer of sediment, the use of solar energy
was mastered and photosynthesis emerged. The further evolution to oxygenic
photosynthesis was effected as catalytic [Mn,Ca]-bearing molecules that otherwise
would have been interred in minerals such as ranciéite and hollandite in shallow
marine manganiferous sediments, were sequestered and invaginated within the
cyanobacterial precursor where, energized by light, they could oxidize water. Thus, a
chemical sedimentary environment was required both for the emergence of
chemosynthesis and of oxygenic photosynthesis, the two innovations that did most to
change the nature of our planet. |
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