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Abstract (2001)

  1. Critical Aspects
  2. Energy Supplies
  3. Flow reactor
  4. Flatbed reactor
  5. Electrochem reactor
  6. The code
  7. Organic membrane
  8. Coda

References

Figures 1-25

The Origin of Life at a submarine alkaline seepage
 Michael J. Russell, Allan J. Hall, Laiq Rahman & Dugald Turner

IV. Flat bed reactor (assemblage)

A natural "flat-bed reactor" and molecular sieve (Anderson and Jackson 1968; El-Kaissy and Homsy1976; Couderc 1985) precipitates and assembles itself on the ocean floor where the alkaline convective updraft meets the acidulous, iron-bearing ocean.

The catalytic reactor comprises sedimentary flocs of ferrous monosulfide and mixed valence iron-magnesium hydroxide (green rust ~[(FeII,Mg)2FeIII(OH)6]Cl): cf. the Tynagh sulfide mound and iron formation (e.g., Derry et al. 1965; Schultz 1966; Russell 1975,1983,1996), the Red Sea metalliferous sulfide and oxide muds (Bischoff 1969; Ross and Degens 1969; Arrhenius (1986,1987) and the Silvermines exhalative-sedimentary sulfide orebody (Taylor and Andrew 198; Boyce et al. 1983) (Figs. 9a,9b).

Transient bubbles, slugs and chimneys are routinely formed during hydrothermal fluidization of such beds (cf. Figs. 9c,9g,9h, 9i, 9j).

The flocs were the precursors to mackinawite (essentially Fe1+xS), greigite (Fe3S4), minor violarite (FeNi2S4), mixed valence iron-magnesium hydroxides and siderite (FeCO3) (Fig. 10).

Mackinawite, greigite and violarite have been proposed as significant prebiotic catalysts (Russell et al. 1994,1998; cf. Huber and Wächtershäuser 1997).

And the double layer hydroxides such as the green rust ~[(FeII,Mg)2FeIII(OH)6]Cl and the iron-magnesium hydroxides are just the "prebiotic" catalysts favoured by Arrhenius (1986), Eschenmoser (1994) and Krishnamurthy et al. (1999) (and see Kassim et al. 1982; Russell and Hall 2001) (Fig. 10).

The feed to the reactor comprised HCHO, HCN, NH3, CO, HS-, vital succour to emergent life (Cairns-Smith 1982).

The formaldehyde and cyanide in particular would have been concentrated by adsorption on the sulfides and hydroxides (Leja 1982; Fuerstenau 1976; Russell et al. 1994; Rickard et al 2001).

Trapped and adsorbed in this bed they oligermerise in alkaline solution to C2-C4 compounds (Reid and Orgel 1967; Ferris et al. 1978; Ferris 1992; Schulte and Shock 1995; cf. Oró & Kimball 1961, 1962).

For example, in these circumstances glycolaldehyde can be generated by the dimerization of formaldehyde.

2HCHO —> HCO.CH2OH

Glyceraldehyde is then generated from the glycolaldehyde by reaction with formaldehyde at pH 10.5, again catalysed by a mixed valence double layer metal hydroxide (Krishnamurthy et al. 1999b).

Also, in this mildly alkaline solution, HCN would have self-condensed to diaminomaleonitrile (Sanchez et al. 1967), an intermediate in the formation of the purine ring, a reaction encouraged by formaldehyde (Ferris & Orgel 1966; Schwartz and Goverde 1982; Ferris and Hagen 1984; Ferris 1992).

The pyrimidines, cytosine and uracil, are formed from guanidine (a hydrolysis product of HCN oligomers) and cyanoacetaldehyde (Ferris et al. 1974).

Vital amino acids would also be synthesised once carbon dioxide had gained access to the mound's interior, and the hydrothermal cyanide, ammonium ion, formaldehyde and hydrosulfide had been concentrated by an order of magnitude.

Hennet et al. (1991) (and see Marshall 1994), synthesised glycine, alanine, aspartate, serine, glutamate, isoleucine, lysine and proline at 150°C in the presence of hydrothermal hydrogen (in sharply descending order of yield) (Fig. 11).

While certain key molecules (e.g. guanine) and molecules (e.g. 3',5' nucleosides) have not been synthesized, in hydrothermal conditions we maintain that there are now more than sufficient grounds for the hypothesis to form the basis for further experimentation.

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Fig 1Figure 1. Model environment for the emergence of life at ~50°C on the floor of a putative Hadean acidulous ocean floor at a submarine alkaline warm seepage (Russell et al. 1994).

Fig 9aFigure 9a. Magnetite/hematite + chert layers constitute the bioturbated Tynagh iron formation, Ireland. Precursor precipitates are likely to have been green rust, e.g., [FeII2FeIII(OH)6]Cl, deposited at a distance at least 200 metres from the hot spring and seepages. This hydrothermal exhalite is about 350 million years old (Derry et al. 1965; Russell 1975,1983).

Fig 9b Photo of laminated sedimentary sulfides and sulfate and superposed seepage mound comprising fine pyrite chimneys and botryoids at Tynagh. This specimen is from the vicinity of the main hydrothermal conduit, but at approximately the same horizon as the iron formation (Banks 1985; and see Russell 1983).

Fig 9cPhoto of polished cross-section through the top of the sulfide mound shown in Fig. 9b. FeS bubbles have been been oxidised to, and overgrown by, later pyrite (FeS2). Pristine FeS "membranes" are ~5mm (Fig. 9i) thick, two to three orders of magnitude thicker than biological membranes (Russell and Hall 1997).

Fig 9gPhoto of polished cross-section through a pyritic 'slug' from Silvermines, a dynamic structural cavity transitional between a bubble and a chimney. of polished cross-section through a pyritic 'slug' from Silvermines, a dynamic structural cavity transitional between a bubble and a chimney.

Fig 9hPhoto of pyrite chimneys from the Silvermines orebody (Larter et al. 1981; Boyce et al. 1983). Field of view 20 mm.

 Fig 9iphoto of pyrite microbialite from Silvermines (Russell 1996b).

Fig 9j Figure 9j. Polished section of iron-sulfide membrane (from Russell & Hall,1997)

 Fig 10Figure 10. Pourbaix diagram demonstrating how the fields of green rust and mackinawite (FeS) are likely to be met as alkaline fluids interface with the acidulous ocean. We have calculated, using Geochemists Workbench (GWB - Bethke 1996), a maximum concentration of HS- of ~10 millimoles (similar to the activity of OH- at 100°C). Although this is sufficient to form an FeS membrane (as well as a membrane comprising green rust), separate compartments are not produced until bisulfide approaches 100 millilmoles (Fig. 9g).

Fig 11Figure 11. Here we project the conditions employed by Hennet et al. (1992) in their synthesis of amino acids upon a putative hydrothermal mound which acts as a natural fluidised- or flat bed reactor (Russell et al. 1994; and see El-Kaissy and Homsy 1976; Couderc 1985).
 

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Abstract (2001)

  1. Critical Aspects
  2. Energy Supplies
  3. Flow reactor
  4. Flatbed reactor
  5. Electrochem reactor
  6. The code
  7. Organic membrane
  8. Coda

References

Figures 1-25


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 Page last updated:
21 December 2001