Table 2.
The Physicochemical Environment of the Origin of Life
| Prebiotic chemistry | Emergence of life | |||
|---|---|---|---|---|
| Parameter | What | How or where | What | How or where |
| Element availability | CHNOPS essential for life | From endogenous and exogenous CHNOPS molecules | Chemical bonding of these elements—CHNO—range in covalency, allowing sufficiently strong yet penetrable bonding among these elements. S and P are also penetrable but not involved in long chain formation. Assembly of atoms into discrete molecules is also a form of molecular complexification. Mutual cooperative interactions between molecules so that self-organization can emerge and function can be expressed. | By enabling stable linear carbon chains while introducing elements with different oxidation-reduction and pH reactivities that allow reactions without destruction (enzymes) or formation of metastable intermediates leading, ultimately, to sustainable, stable products. Within environments which presented free energy, molecular building blocks and conducive gradients of physicochemical properties so as to encourage mutually cooperative molecular interactions in localized spaces. |
| Temperature | Increases the frequency with which energetic molecular collisions can occur; helps pass activation energy barrier | Probability of intermolecular collision is increased, activation energy supplied by thermal means to cross the energy barrier (heat in hydrothermal systems), helps in dehydration for condensations by removal of water | High temperatures will break up molecular bonds (DNA/RNA nucleotides are stable up to 120°C) | Mixture of high T hydrothermal fluids with lower T seawater varies temperature between the two end members according to flux—see gradients, but also advective flux |
| pH | Different chemical processes occur at different pH values | Alkaline-acid hydrothermal fluids; acidic seawater; mixtures of hydrothermal and seawater; e.g., amino acid coupling to produce peptides at high pH and general acid-catalyzed hydrolysis processes at low pH. | Variable pH changes structure and surface properties of colloids, sols, and polymers. Also allows nucleophilic reactions (substitutions), condensation reactions. | Variable pH for protocells, by allowing reversible and irreversible reactions involving CHNO (S, P) components |
| Ionic strength | Helps stabilization and structural organization of organic molecules, spontaneous self-assembly phenomena; gradients are important for physicochemical properties | Complexification processes, e.g., self-assembly, form a concentration of monomers through the formation of surfactant micelles, interfacial adsorption of ionic surfactants and formation of aqueous colloidal crystals | Salts necessary for protocells, but minimum water activity is 0.5 | By changing the surface charge of particles and by changing the properties and stability of micelles. Seawater, hydrothermal, pore water fluids. |
| Energy | Energy is necessary for fueling reactions and primitive metabolisms | e.g., ionizing radiation for prebiotic reactions; energy from exothermic reactions; heat from hydrothermal systems | For primitive metabolism | Assuming that there were, originally, only reduced compounds with various oxidation states (inorganic components) and that organic components delivered to Earth were in variable oxidation states. Oxidation of reduced inorganic compounds, e.g., NH4, NO2, S2, S0, H2 and Fe2+; oxidation of organic compounds produces phosphorylated molecules. |
| Radiation | Useful for some prebiotic reactions but mainly destructive for organic molecules | UV, radiogenic species (U, Th, etc.) | Destructive for biomolecules | By introducing random flaws in the structure of organic molecules. By introducing temporary elevated energy states in inorganic components and transition elements that enable potential bonding with organic components. UV, radiogenic species (U, Th, etc.). |
| Gradients | A means of maintaining systems out of equilibrium | Dissipation of energy. Sinks for this dissipated energy are potential reaction sites … | Necessary for maintaining far-from-equilibrium systems; to gain and dissipate energy, reactants, and products | e.g., temperature, pH, ionic gradients |
| Molecular diffusion | Diffusion of molecules into and out of the above-mentioned compartments to permit molecular reactions | In solvents, e.g., hydrothermal fluids, seawater, pore waters, mixtures | Diffusion of molecules into and out of the above-mentioned compartments to permit molecular reactions | In solvents, e.g., hydrothermal fluids, seawater, pore waters, mixtures |