48 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”Earlier, Cairn-Smith pointed out the importance of clay as a poten-
tial cradle of life.^34 Gunter Wachtershauser suggested that life started on
the surface of a mineral of iron sulfide called pyrite, which has a positive
charge, being able to attract pre-biotic negatively charged molecules,
since most biomolecules are anionic.^46 He later proposed that this took
place on the seafloor near the hydrothermal vents. On these sites the
reducing power of the volcanic exhalations (H 2 S and NH 3 ) led to carbon
fixation on an inorganic substratum of catalytic iron and other transition
metal centers. The pioneer metabolism could become autocatalytic and
build up a layer of organic superstructure on top of the inorganic sub-
structure on the seafloor.^47 A general review on the hypothesis of sub-
marine hydrothermal vents as the nurseries of life has been published.^48
It has been demonstrated in the laboratory that mineral surfaces
promote the polymerization of nucleotides and amino acids. For instance,
polyadenylates containing more than 50 monomers were formed on the
clay montmorillonite, whereas polyglutamates of 55 monomers were
formed on illite.25,49 The results hint at the spontaneous formation of
small RNA and proteins. Montmorillonite is a type of clay consisting of
stacks of sheets, each made up of oxygen, aluminum, silicon, magne-
sium, iron and hydroxyl ion, arranged in regular arrays. It is formed by
the weathering of volcanic ash and is likely to be present on the primitive
Earth. Interestingly, montmorillonite has the ability to catalyze the con-
version of fatty acid micelles into cell-like vesicles, a prototype of plasma
membrane.^50 Thus, montmorillonite takes on an added significance in
the origin of life.
In recent papers, it was demonstrated that, in the presence of
mineral catalysts, a host of life-relevant molecules can originate from
a single compound — formamide (H 2 NCOH) — believed to be pres-
ent on the primeval Earth. At temperatures of 90–160°C, and in the
presence of a variety of minerals (silica, alumina, CaCO 3 , TiO 2 , zeolites,
common clays, kaolin, montmorillonites, olivines and phosphate miner-
als), formamide condenses into a large number of nucleobases (includ-
ing adenine, hypoxanthine, cytosine, uracil, thymine; excluding guanine