Title: Chemosynthesis- vs. photosynthesis-based ecosystems

have been found, leaving the history of the first 600 million years missing. The oldest evidence for life can be traced back to between 3800 and 3500 million years and is based on chemical signatures, putative microfossils, and layered rocks known as stromatolites. Based on phylogenetic analyses it has been suggested that the first organisms were hyperthermophilic prokaryotes living at temperatures above 80°C. These organisms used energy derived from the oxidation of chemical compounds to build up biomass – a mode of life referred to as chemosynthesis. The chemical compounds that are required for chemosynthetic primary production are not distributed evenly on the Earth, but are restricted to particular sites like submarine volcanoes or cavities in deep crustal rocks. Only the advent of another mode of primary production allowed organisms to spread across the whole planet. Unlike chemosynthetic organisms, photosynthetic organism use sunlight as energy source to build up biomass. This innovation increased biological activity by an order of magnitude (Rosing et al., 2006). The oldest photosynthetic organisms were bacteria that produced no oxygen – so called anoxygenic phototrophs. This group of organisms thus provides the means to understand the origin of photosynthesis (Hanada, 2003), a process that dramatically changed the face of Earth. Anoxygenic phototrophs are also held responsible for the production of massive rock formations on early Eart