Modern Mind

10 109 . Since this is more than the number of electrons in the universe, calculated as 10 8 °, Cairns-Smith argued that there has simply not been enough time, or that the universe is not big enough, for nucleotides to have evolved in this way. 7
    His own version was startlingly different. He argued that evolution arrived before life as we know it, that there were chemical ‘organisms’ on earth before biochemical ones, and that they provided the architecture that made complex molecules like DNA possible. Looking about him, he saw that there are, in nature, several structures that, in effect, grow and reproduce – the crystal structures in certain clays, which form when water reaches saturation point. These crystals grow, sometimes break up into smaller units, and continue growing again, a process that can be called reproduction. 8 Such crystals form different shapes – long columns, say, or flat mats – and since these have formed because they are suited to their micro-environments, they may be said to be adapted and to have evolved. No less important, the mats of crystal can form into layers that differ in ionisation, and it was between these layers, Cairns-Smith believed, that amino acids may have formed, in minute amounts, created by the action of sunlight, in effect photosynthesis. This process would have incorporated carbon atoms into inorganic organisms – there are many substances, such as titanium dioxide, that under sunshine can fix nitrogen into ammonia. By the same process, under ultraviolet light, certain iron salts dissolved in water can fix carbon dioxide into formic acid. The crystal structure of the clays was related to their outward appearance (their phenotype), all of which would have been taken over by carbon-based structures. 9 As Linus Pauling’s epic work showed, carbon is amazingly symmetrical and stable, and this is how (and why), Cairns-Smith said, inorganic reproducing organisms were taken over by organic ones.
    It is a plausible and original idea, but there are problems. The next step in the chain of life was the creation of cellular organisms, bacteria, for which a skin was required. Here the best candidates are what are known as lipid vesicles, tiny bubbles that form membranes automatically. These chemicals were found naturally occurring in meteorites, which, many people argue, brought the first organic compounds to the very young Earth. On this reasoning then, life in at least some of its elements had an extraterrestrial beginning. Another problem was that the most primitive bacteria, which are indeed little more than rods or discs of activity, surrounded by a skin, are chiefly found around volcanic vents on the ocean floor, where the hot interior of the earth erupts in the process that, as we have already seen, contributes to sea-floor spreading (some of these bacteria can only thrive in temperatures above boiling point, so that one might say life began in hell). It is therefore difficult to reconcile this with the idea that life originally began as a result of sunlight acting on clay-crystal structures in much shallower bodies of water. 10
    Whatever the actual origin of life (generally regarded as having occurred around 3,800 million years ago), there is no question that the first bacterial organisms were anaerobes, operating only in the absence of oxygen. Given that the early atmosphere of the earth contained very little or no oxygen, this is not so surprising. Around 2,500 million years ago, however, we begin to see in the earth’s rocks the accumulation of haematite, an oxidised form of iron. This appears to mean that oxygen was being produced, but was at first ‘used up’ by other minerals in the world. The best candidate for an oxygen-producer is a blue-green bacterium that, in shallower reaches of water where the sun could get at it and with the light acting on chlorophyll, broke carbon dioxide down into carbon, which it utilised for its own purposes, and oxygen – in other words, photosynthesis. For a time the minerals of the earth soaked up what oxygen was going (limestone rocks captured oxygen as calcium carbonate, iron rusted, and so on), but eventually the mineral world became saturated, and after that, over a thousand million years, billions of bacteria poured out tiny puffs of oxygen, gradually transforming the earth’s atmosphere. 11
    According to Richard Fortey, in his history of the earth, the next advance was the formation of slimy communities of