Biochemical evolution II: Origin of life in tubular microstructures on weathered feldspar surfaces

Mineral surfaces were important during the emergence of life on Earth becau se the assembly of the necessary complex biomolecules by random collisions in dilute aqueous solutions is implausible. Most silicate mineral surfaces are hydrophilic and organophobic and unsuitable for catalytic reactions, bu t some silica-rich surfaces of partly dealuminated feldspars and zeolites a re organophilic and potentially catalytic. Weathered alkali feldspar crysta ls from granitic rocks at Shap, north west England, contain abundant tubula r etch pits, typically 0.4-0.6 mu m wide, forming an orthogonal honeycomb n etwork in a surface zone 50 mu m thick, with 2-3 x 10(6) intersections per mm(2) of crystal surface. Surviving metamorphic rocks demonstrate that gran ites and acidic surface water were present on the Earth's surface by simila r to 3.8 Ga. By analogy with Shap granite, honeycombed feldspar has conside rable potential as a natural catalytic surface for the start of biochemical evolution. Biomolecules should have become available by catalysis of amino acids, etc. The honeycomb mould have provided access to various mineral in clusions in the feldspar, particularly apatite and oxides, which contain ph osphorus and transition metals necessary for energetic life. The organized environment would have protected complex molecules from dispersion into dil ute solutions, from hydrolysis, and from UV radiation. Sub-micrometer tubes in the honeycomb might have acted as rudimentary cell walls for proto-orga nisms, which ultimately evolved a lipid lid giving further shelter from the hostile outside environment. A lid would finally have become a complete ce ll wall permitting detachment and flotation in primordial "soup," Etch feat ures on weathered alkali feldspar from Shap match the shape of overlying so il bacteria.