A possible energetic role of mineral surfaces in chemical evolution

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access

Abstract

The postulated roles of clays and other minerals in chemical evolution and the origin of life are reconsidered in terms of the interaction of these minerals with penetrating sources of energy such as ionizing radiation and mechanical stress. This interaction, including such facets as excitation, degradation, storage, and transfer, is considered here with regard to its profound potential for altering the capabilities of minerals to serve both as substrates for prebiological chemistry and as inorganic prototypic life forms. The interaction of minerals and energy in relationship to surface chemistry is discussed in terms of the spectroscopic properties of minerals, the interaction of energy with condensed phases, some commonly accepted concepts of heterogeneous catalysis in the absence of electronic energy inputs, and some commonly accepted and novel means by which surface activity might be enhanced in the presence of energy inputs.

An estimation is made of the potential contribution of two poorly characterized prebiotic energy sources, natural radioactive decay and triboelectric energy. These estimates place a conservative lower limit on their prebiotic abundance. Also some special properties of these energy sources, relative to solar energy, are pointed out which might give them particular suitability for driving reactions occurring under geological conditions.

Skeletal support for this broadly defined framework of demonstrated and potential relationships between minerals, electronic excitation, and surface reactivity, as applied to chemical evolution, is provided from the results of our studies on 1/1 clays. We have discovered and partially characterized a number of novel luminescent properties of these clays, that indicate energy storage and transfer processes in clays. These luminescent properties are interpreted in relationship to the electron spin resonance phenomena, to provide a basis for estimating the potential significance of energy storage and transduction in monitoring or driving clay surface chemistry.

Consideration of the electronic structure of abundant minerals in terms of band theory and localized defect centers provides a predictive theoretical framework from which to rationalize the capacity of these materials to store and transduce energy. The bulk crystal is seen as a collecting antenna for electronic energy, with the defect centers serving as storage sites.

The clay properties produced by isomorphic substitution appear to be intimately associated with all of the life-mimetic chemical processes that have been attributed to clays. It appears sensible to postulate that the energetic properties of these substitutional defect centers may also be influential in these biomimetic processes: the promotion of surface reactions, storage of information, replication with transfer of information, and asymmetric separation of electrical charges, as well as their more recently hypothesized roles in energy storage and transduction. The identity of the sites implicated in all of the biomimetic functions of clays as well as their capacity for energy storage is seen to offer significant potential for coupling these functions to an environmental energy source. A yet more specific and experimentally testable hypothesis is offered for a new biomimetic process performed by clays. This hypothesis is that energy stored near isomorphically substituted sites provides the energetic basis for the coupled transport of electrical charge and/or electronic energy through the clay layer, which operates via environmental activation of electron/hole mobility. This is to say that mobility of charge/electronic excitation between defect centers serves as the basis for a primordial inorganic electron transport chain.