Phot0, a plausible primeval pigment on Earth and rocky exoplanets.

In view of the existing controversy around the origin of the photosynthesis and, therefore, the first photosynthetic pigments, our work focuses on the theoretical study of a hypothetical first pigment, simpler than those existing today, that collects energy from solar radiation on Earth-like exoplanets. Our theoretical results show that there could exist geochemical conditions that allow the abiotic formation of a primeval pigment that might become sufficiently abundant in the early stages of habitable rocky exoplanets. These conditions would place this pigment before the appearance of life in a very young planet, thanks to chemical routes instead of biochemical transformations. Thus, our results may refute the currently accepted hypothesis that the complex biomolecules that allowed the photosynthesis to be carried out were synthesized through complex and evolved metabolic pathways. In addition, we show that the proposed primeval pigment, which we call Phot0, is also a precursor of the more evolved pigments known today on Earth and demonstrate, for the first time, an abiotic chemical route leading to tetrapyrroles not involving pyrrole derivatives. Our proposal places simple and very abundant raw materials in never-before-proposed geochemical conditions that lead to the formation of biomolecules of biological interest.