Statistical physics and stromatolite growth: new perspectives on an ancient dilemma

This paper outlines our recent attempts to model the growth and form of microbialites from the perspective of the statistical physics of evolving surfaces. Microbialites arise from the environmental interactions of microbial communities (microbial mats). The mats evolve over time to form internally laminated organosedimentary structures (stromatolites). Modern day stromatolites exist in only a few locations, whereas ancient stromatolitic microbialites were the only form of life for much of the Earth's history. They existed in a wide variety of growth forms, ranging from almost perfect cones to branched columnar structures. The coniform structures are central to the heated debate on the oldest evidence of life. We proposed a biotic model which considers the relationship between upward growth of a phototropic or phototactic biofilm and mineral accretion normal to the surface. These processes are sufficient to account for the growth and form of many ancient stromatolities. These include domical stromatolites and coniform structures with thickened apical zones typical of Conophyton. More angular coniform structures, similar to the stromatolites claimed as the oldest macroscopic evidence of life, form when the photic effects dominate over mineral accretion.Comment: 8 pages, 3 figures. To be published in Proceedings of StatPhys-Taiwan 2004: Biologically Motivated Statistical Physics and Related Problems, 22-26 June 200

A case for biotic morphogenesis of coniform stromatolites

Mathematical models have recently been used to cast doubt on the biotic origin of stromatolites. Here by contrast we propose a biotic model for stromatolite morphogenesis which considers the relationship between upward growth of a phototropic or phototactic biofilm ($v$) and mineral accretion normal to the surface ($\lambda$). These processes are sufficient to account for the growth and form of many ancient stromatolities. Domical stromatolites form when $v$ is less than or comparable to $\lambda$. Coniform structures with thickened apical zones, typical of Conophyton, form when $v >> \lambda$. More angular coniform structures, similar to the stromatolites claimed as the oldest macroscopic evidence of life, form when $v >>> \lambda$.Comment: 10 pages, 3 figures, to appear in Physica