The fate of Earth’s ocean

Bounama, C.; Franck, S.; Bloh, Werner von

doi:10.5194/hess-5-569-2001

Cited by 58 publications

(53 citation statements)

References 33 publications

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“…Our modeling supports this. Estimated fluxes range from 5.1 × 10 11 to 1.83 × 10 12 kg/yr for total water cycled back to the mantle and 2.1-2.3 × 10 11 for water currently degassed at MORs [Peacock, 1990;Maruyama, 1999;Bounama et al, 2001;Jarrard, 2003]. Some authors suggest values between 0.06 and 0.3 for the ratio of water that reaches deep mantle, with the specific values depending on the temperature or age of subducted slabs [Rupke et al, 2004].…”

Section: The Magnitude Of Water Recycling and Implication For Mantle mentioning

confidence: 99%

The effects of deep water cycling on planetary thermal evolution

2011

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[1] We use a parameterized convection model to investigate the effects of deep water cycling on the thermal evolution of an Earth-like planet. The model incorporates two water reservoirs, a surface and an interior mantle reservoir. Exchange between the two is calculated using a mantle convection parameterization that allows for temperature-and water-dependent mantle viscosity together with internally self-consistent degassing and regassing parameterizations. The balance between degassing and regassing depends on the average spreading rate of tectonic plates, the amount of water partitioned into melt, the thickness of a mantle melt zone, and of a hydrated layer at the top of subducting plates. Degassing scales with melt zone thickness such that an early period of extensive melting would create a drier and more viscous mantle, shifting the solidus line in a direction that would reduce the melt zone thickness and the rate of mantle heat loss. Coupling a hydrated zone thickness-dependent regassing factor to the model, to mimic water delivery to the mantle via a serpentinized layer, allows for the potential of a reversing point where the overall water flow direction switches from degassing to regassing as the mantle cools. The water effect on viscosity creates a negative feedback that tends to regulate the final amount of water in the mantle so it is not strongly dependent on the initial amount of planetary water. The final amount of water in the surface reservoir is then determined by this feedback effect together with the initial water budget of the entire planet. This implies that if the initial water budget of a planet can be estimated, from planetary formation models, then the volume of surface water can be used to estimate the volume of water in the mantle of an Earth-like planet. Applying this methodology to the Earth leads to predictions for water concentration in the Earth's mantle that are in line with geochemical and petrological constraints.

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Section: The Magnitude Of Water Recycling and Implication For Mantle mentioning

confidence: 99%

The effects of deep water cycling on planetary thermal evolution

2011

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“…A fundamental drawback to the evaporite model is the sustainability of catalysis: any pond so envisaged has to dry up and refill without a washout very many times before something like a living system can arise, which is hard to imagine given the absence of continents, high and highly frequent tides and 10 km deep oceans at ca. 4 Gyr (Gaffey 1997;Bounama et al 2001;Glasby & Kasahara 2001;Kamber et al 2001). The notion of Hadean oceans chock-full of Oparin's prebiotic soup still enjoys some popularity (Bada & Lazcano 2002), but the question remains of how a solution at equilibrium can start doing chemistry.…”

Section: Unanswered But Not Unanswerable Questionsmentioning

confidence: 99%

On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells

Martin

Russell

2003

Phil. Trans. R. Soc. Lond. B

719

621

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All life is organized as cells. Physical compartmentation from the environment and self-organization of self-contained redox reactions are the most conserved attributes of living things, hence inorganic matter with such attributes would be life's most likely forebear. We propose that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH and temperature gradient between sulphide-rich hydrothermal fluid and iron(II)-containing waters of the Hadean ocean floor. The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyse the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments, which furthermore restrained reacted products from diffusion into the ocean, providing sufficient concentrations of reactants to forge the transition from geochemistry to biochemistry. The chemistry of what is known as the RNA-world could have taken place within these naturally forming, catalyticwalled compartments to give rise to replicating systems. Sufficient concentrations of precursors to support replication would have been synthesized in situ geochemically and biogeochemically, with FeS (and NiS) centres playing the central catalytic role. The universal ancestor we infer was not a free-living cell, but rather was confined to the naturally chemiosmotic, FeS compartments within which the synthesis of its constituents occurred. The first free-living cells are suggested to have been eubacterial and archaebacterial chemoautotrophs that emerged more than 3.8 Gyr ago from their inorganic confines. We propose that the emergence of these prokaryotic lineages from inorganic confines occurred independently, facilitated by the independent origins of membrane-lipid biosynthesis: isoprenoid ether membranes in the archaebacterial and fatty acid ester membranes in the eubacterial lineage. The eukaryotes, all of which are ancestrally heterotrophs and possess eubacterial lipids, are suggested to have arisen ca. 2 Gyr ago through symbiosis involving an autotrophic archaebacterial host and a heterotrophic eubacterial symbiont, the common ancestor of mitochondria and hydrogenosomes. The attributes shared by all prokaryotes are viewed as inheritances from their confined universal ancestor. The attributes that distinguish eubacteria and archaebacteria, yet are uniform within the groups, are viewed as relics of their phase of differentiation after divergence from the non-free-living universal ancestor and before the origin of the free-living chemoautotrophic lifestyle. The attributes shared by eukaryotes with eubacteria and archaebacteria, respectively, are viewed as inheritances via symbiosis. The ...

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“…Because the dehydration reactions that control the amount of water recycled to the mantle are temperature dependent, the Hadean mantle was drier than its modern counterpart. The ocean contained most of the Earth's water and its volume may have been up to twice that of today's oceans (Bounama et al, 2001). Upwelling of hot, dry mantle at oceanic spreading centres generated an early Archaean crust about 30 km thick (Sleep and Windley, 1982;Arndt and Chauvel, 1990) ( Fig.…”

Section: Crustal Structure and Compositionmentioning

confidence: 99%

Geodynamic and metabolic cycles in the Hadean

2005

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Abstract. High-degree melting of hot dry Hadean mantle at ocean ridges and plumes resulted in a crust about 30 km 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 H 2 to the deep ocean made acidulous by dissolved CO 2 and minor HCl derived from volcanoes. Away from ocean ridges, submarine hydrothermal fluids were cool (≤100 • C), alkaline (pH ∼10), highly reduced and also H 2 -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 (Fe 5 NiS 8 ). 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 wouldCorrespondence to: N. T. Arndt (arndt@ujf-grenoble.fr) 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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The fate of Earth’s ocean

Cited by 58 publications

References 33 publications

The effects of deep water cycling on planetary thermal evolution

The effects of deep water cycling on planetary thermal evolution

On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells

Geodynamic and metabolic cycles in the Hadean

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