Cairns-Smith

However, there are also biogenesis models which do not require phosphate, such as the inorganic hypothesis of the origin of life proposed by Cairns-Smith (see Sect. 7.1), the thioester world proposed by de Duve (see Sect. 7.4) or the sulphur-iron world suggested by Wachtershauser (see Sect. 7.3). The RNA world (see Chap. 6), however, cannot exist without phosphate. 

The use of reactive surfaces for the specific synthesis of biomolecules, or as a model for replication processes, was first reported by Cairns-Smith and Weiss (see Sect. 7.1) and continued by G. Wachtershauser (see Sect. 7.3), as well as J. Ferris and L. Orgel. It was thus appropriate to study the stabilisation of the reaction partners in enzyme-free self-replication at surfaces with reactive properties. As early as 1995, the group of G. von Kiedrowski (then at Freiburg, Germany) bonded reacting molecules at surfaces and then added the other required reaction components to the system in a stepwise manner (the latter process is referred to as feeding ). 

According to Cairns-Smith, the first primitive gene materials could have been clay minerals these crystallize out everywhere on Earth from dilute silica solutions and hydrated solutions of metal ions. Both groups of substances are continually being formed by weathering processes. Two cycles keep this dynamic process going ... 

Cairns-Smith is careful enough to concede that the first hypothetical informationcarrying material was not of necessity a clay mineral however, the basic features of the model can best be demonstrated using different clay species. Thus, for example, clays could have crystallized out in sandstone pores from solutions containing products derived from weathering. The result would have been clay layers, which could have been separated and transported further by external influences replication under similar conditions would have followed. Such crystallization processes would have also involved errors, such as defects, vacancies, and the incorporation of other ions or atoms these inorganic mutations would have been passed on, i.e., they would have been incorporated into the next sheet to be formed. 

Clays consist of parallel silicate layers in kaolinite, two unsymmetrical types of layers are linked by hydrogen bonds. One consists of aluminium ions and hydroxyl groups, the other of silicon and oxygen ions. Cairns-Smith does not postulate a detailed mechanism, but only describes the main thrust of his argument. Critics complain that clear experimental results are not available (however, other proponents of new hypotheses often provide no evidence to back up their suggestions ). 

Only some biogenesis researchers will agree wholeheartedly with these seven clues however, two of the concepts presented by Cairns-Smith will certainly be widely supported ... 

Cairns-Smith, as the leading proponent of the mineral theory, has also shown interest in both the hydrothermal biogenesis theory (Cairns-Smith, 1992) and the iron-sulphur hypothesis proposed by G. Wachtershauser (see Sect. 7.3). 

An information science research group devised a new model which could explain information storage in the prebiotic phase of the biogenesis process. They assume that layered double hydroxide (LDH) minerals acted as proto-RNA molecules on the young Earth about 4 billion years ago. This hypothesis relates to Cairns-Smith s genetic takeover thesis, which thus again became the subject of discussion. 

Bernhard G, Ludemann HD, Jaenicke R, Konig H, Stetter KO (1984) Naturwissenschaften 71 583 Blochl E, Keller M, Wachtershauser G, Stetter KO (1992) Proc Natl Acad Sci USA 89 8117 Broil D, Kaul C, Kramer A, Krammer P, Ricter T, Jung M, Vogel H, Zehner P (1999) Angew Chem 111 3180, Int Ed 38 2998 Cairns-Smith AG (1966) J Theor Biol 10 53... 

Cairns-Smith AG (1985a) Seven Clues to the Origin of Life. Cambridge University Press Cairns-Smith AG (1985b) Scientific American, June p 74 Cairns-Smith AG (1992) Orig Life Evol Biosphere 22 161 Choughuley ASU, Lemmon RM (1966) Nature 210 628... 

Cairns-Smith, A. G. Hartman, H. Clay Minerals and the Origin of Life Cambridge University Press Cambridge, 1986. 

Cairns-Smith s original approach may sound different from Morowitz s approach mentioned earlier but in fact it also postulates a kind of metabolism without and prior to enzymes. 

Independently, there was the discovery in 1979 of the richness of organic compounds in hydrothermal hot vents (see for example Holm et al., 1992, and Chapter 3). The idea was fully developed by Wachtershauser (1988) and Cairns-Smith et al. (1992), and (of course) became another world. Life then began with the reduction of CO2 and N2 coupled with the reducing power of pyrite formation - and so was born the iron-sulfur-world hypothesis. Thus, the work of Wachtershauser also represents a link between the field of surface catalysis and the field of hydrothermal vents. 

Cairns-Smith, A. G., Hall, A. J., and Russell, M. J. (1992). Mineral theories of the origin of life and an iron sulphide example. Orig. Life Evol. Biosph., 22,... 

Cairns-Smith, A. G. (1982). Genetic Takeover and the Mineral Origin of Life. Cambridge University Press. 

Bullard, T., Freudenthal, J., Avagyan, S. and Kahr, B., Test of Cairns-Smiths crystals-as-genes hypothesis ,... 

Theories for even earlier forms of mutateable transmission of genetic information have involved clay minerals. Montmorillonite clay particles have been demonstrated to catalyse the condensation of nucleotides and we discussed in Section 8.2.8 the Cairns Smith hypothesis of how crystal dislocations could transmit some form of genetic information. Most hypotheses about clays have yet to be demonstrated experimentally, however. 

Cairns-Smith C (1992) In Tran Thanh VanJ, MounolouJC, Schneider J, McKay C (eds) Frontiers of life. Editions Frontieres, Gif-sur-Yvette, France, pp 119-132... 

Concentration of the organic reactants on surfaces or in the pores of clay materials prior to reaction has been suggested by Bernal [219] and Cairns-Smith [220]. Pores of different sizes might have operated as prebiotic reactors for asymmetric synthesis, since within their confined environment one may find chiral catalytic sites as well as chiral surfaces. One could envisage that such pores might have provided a plausible environment for the formation of diastereoisomeric self-assemblies of the types described in this review and as required for the stochastic mirror symmetry breaking scenarios. In addition, within such pores the chiral material once formed would be protected from racemization that could have been induced by impact with heavy bodies or by intense cosmic radiation. 

Cairns-Smith G (1986) Clay minerals and the origin of life. Cambridge University Press, Cambridge... 

Cairns-Smith, A.G. 2002. The origin of life Clays. Pp. 169-192 in Frontiers of Life, Volume 1 (D. Baltimore, R. Dulbecco, F. Jacob, and R. Levi-Montaldni, eds.). Academic Press, San Diego, Calif. 

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