Clay minerals and the origin of life

‘At the heart of the problem of the origin of life lies a fundamental question: what is it exactly we are trying to explain the origin of’. That crucial question leads off the first chapter of the latest saga in the attempt to know the unknowable. However, posing the question is the nearest this book comes to an examination of it. The question of origins will continue to excite, stimulate and intrigue while men have breath to draw but it can be put another way. If we can really understand what makes the critical difference between living and non-living, if we comprehend exactly what is the essence of life, then the question of origins might seem obvious, even trivial. There have been many suggestions in the past as to the critical property: replication, genes, catalytic activity, nucleic acids, proteins, hydrophobic forces, open systems, network interactions, conflicts of activity with stability, complexity, homeostasis, error tolerance, growth, feedback to name but a few. Is it any one of these? Or is it all of them? Ecological locations of the origin are equally diverse. These range from the atmosphere, ocean depths, clays, seashores, ocean vents, surface of the sea, volcanoes, warm little ponds and so on. Quite evidently firm decisions are hard to come by on the origin of life and this explains the plethora of differing views. Noone can decide and predilections one way or the other seem as much the result of bias and training as anything else. In my view the difficulty that this book faces is that it has effectively plumped for replication and catalytic activity as being the two most primitive features of a recognisable living system. The ethos behind the book regards nucleic acid and proteins as molecules whose specific formation and accumulation were highly improbable on the early earth. It suggests instead that replication and catalytic activity were initially subsumed by clays and only later taken over by present-day enzymes and DNA. This book is, in part, about that possibility. It deals with the types of clays, clay synthesis, clays on the early earth, Mars and in meteorites and discusses clays as catalysts and putative genes. It is not for the casual reader. The structure and chemistry of clays occupies a substantial part of the book reflecting no doubt the departmental location of the main editor. But it is a book about the clay-life hypothesis which is of current interest. If we believe that the origin of life was a gradual process (and I am not sure that I have ever seen that properly justified) then we can place some temporal order in the supposed specific characteristics of living systems. On this basis open systems, feedback, homeostasis and network interactions have to precede all the rest since in a fluctuating environment continuation, maintenance and stability are essential conditions of survival. Is it conceivable that replication or growth or even good catalytic activity could sensibly occur without internal stability or without error tolerance or without a flux of energy? 150 years ago Claude Bernard stated that “the stability of the internal milieu was the condition of free and independent life”. While he was not referring to primordial living systems but to temperature control in mammals his statement is equally applicable. The threshold separating the non-living from the living might simply reflect a critical degree of complexity in interaction specifying a minimal homeostatic capability. Unless clays demonstrably contribute to homeostasis then the supposed attention they have achieved as early life progenitors is misplaced. Since I do not think they do I would regard this book and its ideas as peripheral to the main stream of understanding of origins. If you think replication and catalytic activity are the fundamental characteristics then this book is written for you.