Constraints on Photosynthesis on Earth and Earth-Like Planets

Abstract

We discuss how the spectral mismatch between solar radiation at the Earth's surface and the two absorption maxima (440 and 680 nm) of the dominant chlorophyll pigments can be explained as an evolutionary accident of the marine habitat in which photosynthesis evolved on Earth. The geometric rigidity and great stability of chlorophyll make it a likely “universal pigment” given this, together with the spectral absorption properties of water, the evolution of photosynthesis on Earth-like planets (ELPs) orbiting in the habitable zones of A, F and G stars should be relatively straightforward. However for ELPs orbiting cool K and M stars, the effects of variable UV emission from the ELP at earlier epochs and the high absorption of red light by water could lead to a “feast and famine” existence for photosynthetic organisms in the ELP ocean. Pull exploitation of the cool star radiation when UV activity has declined may lead to an evolution of the photosynthetic machinery from the terrestrial two photon to a three photon system.