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1 Introduction 1 Field-control, phase-transitions, and life’s emergence 2 3 4 Gargi Mitra-Delmotte 1* and A.N. Mitra 2* 5 6 7 139 Cite de l’Ocean, Montgaillard, St.Denis 97400, REUNION. 8 e.mail : [email protected] 9 10 2Emeritius Professor, Department of Physics, Delhi University, INDIA; 244 Tagore Park, 11 Delhi 110009, INDIA; 12 e.mail : [email protected] 13 14 15 16 17 18 19 *Correspondence: 20 Gargi Mitra-Delmotte 1 21 e.mail : [email protected] 22 23 A.N. Mitra 2 24 e.mail : [email protected] 25 26 27 28 29 30 31 32 33 34 35 Number of words: ~11748 (without Abstract, references, tables, and figure legends) 36 7 figures (plus two figures in supplementary information files). 37 38 39 40 41 42 43 44 45 46 47 Abstract 48 49 Critical-like characteristics in open living systems at each organizational level (from bio- 50 molecules to ecosystems) indicate that non-equilibrium phase-transitions into absorbing 51 states lead to self-organized states comprising autonomous components. Also Langton’s 52 hypothesis of the spontaneous emergence of computation in the vicinity of a critical 53 phase-transition, points to the importance of conservative redistribution rules, threshold, 54 meta-stability, and so on. But extrapolating these features to the origins of life, brings up 55 a paradox: how could simple organics-- lacking the ‘soft matter’ response properties of 56 today’s complex bio-molecules--have dissipated energy from primordial reactions 57 (eventually reducing CO 2) in a controlled manner for their ‘ordering’? Nevertheless, a 58 causal link of life’s macroscopic irreversible dynamics to the microscopic reversible laws 59 of statistical mechanics is indicated via the ‘functional-takeover’ of a soft magnetic 60 scaffold by organics (c.f. Cairns-Smith’s “crystal-scaffold”). A field-controlled structure 61 offers a mechanism for bootstrapping-- bottom-up assembly with top-down control: its 62 super-paramagnetic colloidal components obey reversible dynamics, but its dissipation of 63 magnetic (H)-field energy for aggregation breaks time-reversal symmetry. Its responsive 64 adjustments to environmental changes would bring about mutual coupling between 65 random organic sets supported by it via a self-organized-criticality-like mechanism. 66 Further, these adjustments of a cooperative network could alter its capacity to assist a 67 spontaneous process, thus enabling the selection of the functional configuration. A non- 68 equilibrium dynamics could now drive the kinetically-oriented system (trimming the 69 phase-space of sterically-coupled organics) towards a series of phase-transitions with 70 appropriate replacements “taking-over” its functions. Where available, experiments are 71 cited in support of these speculations and for designing appropriate tests. 72 73 Key words: field-controlled colloids; proto-metabolic cycle; slow driving; long-range 74 correlation; organic “takeover”; phase-transition; feedback 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 1 Introduction 94 95 The implications of minerals in life’s emergence were first envisaged by Goldschmidt 96 (1952) and Bernal (1949); these included concentration (adsorption) and catalysis, 97 besides chirality of organics via association with crystal-surfaces. This motivated many 98 works (see Arrhenius 2003; Carter 1978; Ferris 1999; Hazen and Sverjensky 2010; 99 Jacoby 2002; Lahav 1999; Lambert 2008; Schoonen et al 2004; Seigel and Seigel 1981, 100 and references therein), and inspired scenarios exploring the resemblance of ancient 101 enzyme-clusters to mineral ones in metabolism-first approaches to life’s origins (Cody et 102 al 2000; McGlynn et al 2009; Russell and coworkers (Sect.6.3); Wachtershauser 1988). 103 Hazen (2006) reviews the role of mineral surfaces for assistance at two stages of 104 increasing complexity, viz. (1) the emergence of biomolecules, and (2) the emergence of 105 macromolecular systems. These in turn cover three aspects: (i) possible enhanced self- 106 assembly of lipids in the presence of minerals (Deamer and Pashley 1989; Luisi 1989; 107 Hanczyc et al 2003; Chen et al 2004); (ii) polymerization of amino acids and nucleic 108 acids, (Sowerby 1996; Uchihashi et al 1999; Lahav et al 1978; Ferris 1993; Liu and Orgel 109 1998; Orgel 1998) where Smith (1998) uses channels of zeolites as a packing constraint 110 to help polymerization; and (iii) the selective adsorption onto mineral surfaces, of organic 111 species (Churchill et al 2004; Carter 1978; Lowenstam and Weiner 1989). The latter 112 include chiral molecules (Lahav 1999; Jacoby 2002; Hazen and Sholl 2003), although 113 Hazen (2006) also mentions other mechanisms for chiral selection grouped under 114 determinate vs chance local processes. As a universal determinate influence, he notes the 115 parity violation in beta-decay; for more local ones, the chiral-selective photolysis by 116 circular-polarized synchrotron radiation from neutron stars (Bailey et al. 1998; Podlech 117 1999) or magnetochiral photochemistry (Rikken and Raupach 2000); and at smaller 118 scales the amplification of slight chiral excesses via Bose-Einstein condensation (Chela- 119 Flores 1994), or chiral self-assembly of polymers (Bolli et al. 1997; Lippmann and Dix 120 1999; Saghatelian et al. 2001) or simply crystals (Eckert et al. 1993; Lahav and 121 Leiserowitz 1999). According to Hazen (2006), Cairns-Smith’s (1968) theory is the most 122 extreme form of mineral-based hypotheses positing that clay crystals were the precursors 123 of today’s replicators. 124 125 As we see it, in this two-level scenario, the hosting inorganic layer or the crystal- 126 organization—call it level-I (depicted as a white pin board in Figure 1a), -- offers top- 127 down control and assistance for the bottom-up assembly of organic materials into 128 complex patterns building up from randomly reacting/interacting entities in the ‘guest ’ 129 layer—call it level-II (depicted with coloured beads, lower Figure 1a). In the latter, 130 chemical reactions lead to building blocks, small polymers, proto-metabolic reactions, 131 etc. while weak physical interactions (e.g. Hunding et al 2006) lead to small assemblies. 132 Now, level-I’s own crude functional organization acts as a selection/’trimming’ 133 mechanism for ‘fishing out’ constructs with superior information-propagation capacity 134 from the multitude of species forming at level-II. This leads to a gradual replacement of 135 the inorganic organization by organic modules (coloured pattern, upper Figure 1a), where 136 the latter’s recruitment by a functional system --aided by complementary interactions-- is 137 crucial for their dynamic stability (see Sect.3); conceptually too, this relates structure of 138 the organic module to its function . Also, level-II products favouring propagation of 139 template-information (level-I) enable feedback between the levels. But, compared to hard 140 crystals, a soft fractal organization seems a more natural origin for bio-complexity 141 (Sect.2). To that end, a colloidal-gel scaffold (Sect.6) seems promising as a dynamically 142 stable confining medium compatible with the key role of diffusion-controlled reactions in 143 cellular biochemistry (Kopelman 1989; Konkoli 2009). A gradual ‘takeover’ by organic 144 modules is also easier to visualize via a dynamic inorganic modular organization, e.g. soft 145 colloids (Russell et al 1990), provided one can associate them with a crystal-like 146 organization, towards a formal theory. 147 148 Now, in contrast to mineral-based bottom-up approaches adhering to the “metabolism- 149 first” camp, the crystal-scaffold theory proposes a pre-existing template-organization, and 150 thus upholds the “genes-first” one. The former tells how local mineral-organic 151 interactions can assist guest-level-II reactions, while the latter considers the global 152 aspects, i.e., bio-like functions linked to a cooperative organization of mineral-hosts. 153 Indeed, these are complementary, and roughly correspond to the 2-tier organization of 154 living systems: the control-network-level-I of complex biomolecules (proteins, nucleic 155 acids, lipids, carbohydrates, etc) maps to the hosting functional mineral-organization, and 156 the metabolic network-level-II to the (guest) organic reactions/interactions. In the federal- 157 like anatomy of a living system, each tier/sub-system functions independently—yet 158 constrained by feedback-coupling. Now, the second correspondence-- between guest 159 reactions/interactions and metabolic-network-level-II-- is easier to visualize, but the first 160 one is not so obvious (see Sect.3). And while macroscopic energy flow in the metabolic 161 reaction cycles can be mapped to that in similar organic attractors in abiogenesis, we still 162 need a mapping -- albeit in terms of inorganic matter-- for the control-network (level-I) 163 capable of microscopic energy transactions . This can be seen at the level of the 164 components that can undergo infinitesimal conformational changes to traverse a 165 continuous energy landscape, or even at the global system level, where diverse closely 166 spaced states in genotype-space are accessible via environmental fluctuations. Sure 167 enough, open living systems can harness fluctuations --at component (for work-cycles) 168 and (evolving) system levels—in sharp contrast to technological devices, sealing off 169 external noise. 170 171 Indeed, a self-organized criticality (SOC; Sect.2) mechanism for the slow evolution of 172 environment-susceptible bio-systems (levels I and II) helps understand the emergence of 173 complexity in them, despite the absence of a predictable framework. But in the origins of 174 life, the role of SOC is limited if only guest-level-II processes are to be considered, for 175 proto-metabolic reactions or weak interactions between organics dispersed in random 176 mixtures alone cannot suffice for SOC to be effective. [As for relative orders 177 of magnitude, bond energies involved in covalent bonds vs those for Van der Waals 178 clusters bear the ratio: several eV vs a fraction of an eV (Kreuzer 2005), compared to 179 thermal energy (k BT) of ~ hundredth of an eV].
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