Parsons I, Lee M R, Smith J V
Department of Geology and Geophysics, University of Edinburgh, Edinburgh EH9 3JW, United Kingdom.
Proc Natl Acad Sci U S A. 1998 Dec 22;95(26):15173-6. doi: 10.1073/pnas.95.26.15173.
Mineral surfaces were important during the emergence of life on Earth because 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, but some silica-rich surfaces of partly dealuminated feldspars and zeolites are organophilic and potentially catalytic. Weathered alkali feldspar crystals from granitic rocks at Shap, north west England, contain abundant tubular etch pits, typically 0.4-0.6 microm wide, forming an orthogonal honeycomb network in a surface zone 50 microm thick, with 2-3 x 10(6) intersections per mm2 of crystal surface. Surviving metamorphic rocks demonstrate that granites and acidic surface water were present on the Earth's surface by approximately 3.8 Ga. By analogy with Shap granite, honeycombed feldspar has considerable 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 would have provided access to various mineral inclusions in the feldspar, particularly apatite and oxides, which contain phosphorus and transition metals necessary for energetic life. The organized environment would have protected complex molecules from dispersion into dilute solutions, from hydrolysis, and from UV radiation. Sub-micrometer tubes in the honeycomb might have acted as rudimentary cell walls for proto-organisms, which ultimately evolved a lipid lid giving further shelter from the hostile outside environment. A lid would finally have become a complete cell wall permitting detachment and flotation in primordial "soup." Etch features on weathered alkali feldspar from Shap match the shape of overlying soil bacteria.
在地球生命起源过程中，矿物表面至关重要，因为在稀水溶液中通过随机碰撞组装必要的复杂生物分子是不太可能的。大多数硅酸盐矿物表面是亲水且憎有机的，不适合催化反应，但部分脱铝长石和沸石的一些富含二氧化硅的表面是亲有机的且具有潜在催化性。来自英格兰西北部沙普花岗岩的风化碱性长石晶体含有丰富的管状蚀刻坑，通常宽0.4 - 0.6微米，在50微米厚的表面区域形成正交蜂窝状网络，每平方毫米晶体表面有2 - 3×10⁶个交叉点。现存的变质岩表明，花岗岩和酸性地表水在大约38亿年前就已出现在地球表面。类比沙普花岗岩，蜂窝状长石作为生物化学演化起始的天然催化表面具有相当大的潜力。生物分子应该是通过氨基酸等的催化作用而形成的。蜂窝状结构可以使长石中的各种矿物包裹体，特别是含有高能生命所需的磷和过渡金属的磷灰石和氧化物得以接触。这种有组织的环境可以保护复杂分子不分散到稀溶液中，不被水解，也不受紫外线辐射。蜂窝状结构中的亚微米管可能充当了原始生物的原始细胞壁，这些原始生物最终进化出了脂质盖，进一步抵御恶劣的外部环境。脂质盖最终可能变成了完整的细胞壁，使原始生物能够脱离并漂浮在原始“汤”中。沙普风化碱性长石上的蚀刻特征与覆盖其上的土壤细菌形状相符。
