Origin of Life

Theories and evidence for chemical biopoieses

Cairns-Smith model

ScienceWeek: Modified: "in 1982, the chemist A.G. Cairns-Smith suggested that life developed from crystals, with organic evolution coupled to the replication of clay crystals. In the Cairns-Smith model, life is envisaged as beginning through the influence of natural selection on the growth of inorganic crystals. Clay structures are conceived of as the first carriers of genetic information. Replication is viewed as occurring by the accidental detachment of layers in the clay
lattice, these layers serving as nuclei for the growth of new daughter molecules. Later, organic chemicals were incorporated into the structure of the replicating crystallites. Competition favored those systems that were more adaptable by virute of employing used organic molecules to carry out their functions. Nucleic acids (RNA and DNA) evolved next, and replaced clay crystals as the basic information repository making up the genes of the organism. Under the pressure of natural selection, the original clay-mineral component was dispensed with entirely."

Clay Material May Have Acted As 'Primordial Womb' For First Organic Molecules: "Williams' research suggests how some of the fundamental materials necessary for life might have come into existence deep in the sea. The results of Williams' experiments were published in the article, "Organic Molecules Formed in a Primordial Womb," in the November issue of Geology.Williams and her team mimicked the conditions found in hydrothermal vents along the lines where tectonic plates converge on the ocean floor. The vents are fissures in the seafloor that spew out super-hot water much like an underwater volcano.From earlier work, the researchers knew that with high enough temperatures and pressure, volcanic emanations could produce the chemical compound methanol. What scientists did not know was how the methanol could survive intense temperatures of 300 to 400 C.Williams and her team simulated the intense heat and pressure of the ocean floor within a pressurized vessel. The reaction of the clay and methanol was monitored over six weeks. The team found that the expandable clay not only protected the methanol, but also promoted reactions that formed even more complex organic compounds. The mineralogical reaction between the clay and methanol was facilitating the production of new organic material.Scientists theorize that the diverse organic molecules protected within the clay might eventually be expelled into an environment more hospitable to life, leading to an 'organic soup.' What makes the finding so exciting is that the experimental conditions reflect scientists' best estimations of the simplest conditions that likely existed when life began, Williams said."

Adsorption On Clay Accounts For Organic-Rich Rocks: "Kennedy explained that smectite crystals bear a large charged surface area that is attractive to organic molecules. As smectite sinks through sea water it adsorbs carbon-rich molecules into its intercrystalline surfaces.The existence of organic matter on smectite surfaces also helps understand an important process -- natural clay catalysis -- in the formation of petroleum."

Differential Adsorption of Nucleic Acid Bases: ScienceWeek: Modified: "Researchers nowreport they have determined the equilibrium adsorption isotherms for the nucleic acid purine and pyrimidine bases dissolved in surface water on crystalline graphite. The bases exhibited different adsorption behavior, generating an elution series: guanine > adenine > hypoxanthine > thymine > cytosine > uracil. Such differential adsorption properties may have been relevant to the prebiotic chemistry of the bases, and may have influenced the composition of the primordial genetic architecture."S.J. Sowerby et al: Proc. Natl. Acad. Sci. US 30 Jan 01 98:820


Anonymous Anonymous said...

If the PubMed link takes you to the Search page rather than the article, simply copy and paste the Title.

12:07 PM  

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