ABSTRACT

The triple convergence of genetic code structure, atmospheric amino acid synthesis and meteoritic amino acids establishes the heterotrophic nature of the first living cell (Section 1.4). To develop a heterotrophic living cell, a range of biomolecules would have to be sourced from the environment, including building blocks of RNA, proteins, cell membrane and the energy resources to piece them together. Therefore prebiotic chemistry has to identify feasible routes for sourcing organic compounds from either prebiotic synthesis on Earth, or extraterrestrial delivery via meteorites or interstellar dust. The criteria for a meaningful prebiotic synthesis are as follows:6

a. The proposed prebiotic synthesis must be plausible with the starting materials being present in adequate amounts at the site of synthesis;

b. The conditions employed must be consistent with the prebiotic atmosphere and environment (Section 8.3);

c. The reaction must occur in water or in the absence of a solvent;

d. The yield of the reaction must be significant. These criteria help to decide which model abiotic reactions can be

prebiotic and which cannot based on current knowledge. In practice, sometimes optimism may be justified retroactively. For example, it is well known that the formose reaction can give rise to sugars including ribose for the production of RNA, but the yield of ribose is usually so low that doubts have arisen whether ribose synthesis by the formose reaction could be regarded as prebiotic*. However, recent discoveries of high yields of ribose by the formose reaction have increased the ‘prebiotic-ness’ of this plausible source of ribose.