Prebiotic Evolution: The Self-Assembly of Primordial Biomolecules

Abiogenesis is a prebiotic evolution, an interacting network of primordial prebiomolecules. We can gain insight into how this network developed by examining molecular fossils available on Earth and in space. Initial investigations were limited to studies that could be conducted from the Earth’s surface, the composition of meteorites, particularly the carbonaceous chondrites, and spectroscopy within the optical, infrared, and radio bands. Radio astronomy revealed the rich mix present in the interstellar medium, from which spectroscopic measurements have detected more than 300 molecular fossils that occupy niches on the path to life. Mass spectrometry of meteorites showed that many prebiomolecules spontaneously self-assembled protected by shadowing from the radiation environment of outer space. With the advent of space exploration, several other important sources of molecular fossils became available, including the compositions of planets, comets, and asteroids. The result of this data storm was to find that prebiomolecules were found everywhere one looked. Polycyclic aromatic hydrocarbons, the kind that are produced in your charcoal grill, were found to be ubiquitous. Early parallel laboratory experiments, begun by Stanley Miller, showed how easy it was to form amino acids, the constituents of proteins. The self-assembly of amino acids into peptides was subsequently demonstrated. The presence on Earth of phosphorus, a rate-limiting ingredient in life, is examined. Recent data from the sample-return mission to Ryugu indicates that nucleic acid bases spontaneously formed during the 4.5-GYa asteroid-forming epoch in the evolution of the solar system. We also review the formation of nucleic acids, the purines and the pyrimidines, as well as the synthesis of essential ribose and both the nucleosides and nucleotides, and the nucleic acid polymers. The prebiotic synthesis of carbohydrates and lipids is presented as a fait accompli.