Clays and Life

In the beginning of the 1980s Cairns-Smith proposed that clays prodnced from igneons rock weathering facilitated biochemical evolntion. This model is shown schematically in Eignre 21. 

However, this clay-life theory has many weaknesses as well. The main restriction is related to the unclear abundance of sites suitable for clay evolution. The input of photic energy is also uncertain. There is little information on the kinds of clay that might have existed prior to 3.5 billion years ago. This is very important because the properties of clay would have played a crucial role in organic synthesis and not all clays may be suitable for crystal genes. 

This model is also unable to explain microbial phylogeny. For example, the origins of thermophily, sulfur metabolism, and the differentiation of Bacteria and Archaea are not immediately apparent. There are some other specific constraints of clay-life theory and those who are interested can find the details in T. Fenchel et al., 1998 (see Further reading list). 

Pyrite provides also a surface for stabilizing and protecting reaction of synthesis. These reactions lead ultimately to complex polymerizations and early cellularization by incorporation of pyrite grains. 

Unlike two previous theories of life origin, only a few pieces of experimental evidence exist at present to prove the theoretical speculations. However, we have to notice the verification of the basic mechanism of molecular hydrogen generation as a reducing power, furthermore, the amide bond synthesis has been also demonstrated, both at temperatures within the range of hydrothermal vents (100 °C). In addition, the evidence for at least sulfide-based amino acid synthesis and polymerization from simple precursors has been shown. The formation of acetic acid and an activated thioester from carbon monoxide, methanethiol and various combinations of ferrous and nickel sulfides has been experimentally proved as well. However, further verification is necessary for the modes and rates of organic synthesis. 

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