Meteorites and the RNA World: Synthesis of Nucleobases and Ribose in Carbonaceous Planetesimals and the Role of Initial Volatile Content
The origin of life might be sparked by the polymerization of the first RNA molecules in Darwinian ponds during wet-dry cycles. The nucleobases (adenine, guanine, cytosine, uracil, thymine [DNA]) and the sugar ribose are key life-building blocks and were found in carbonaceous chondrites. Their exogenous delivery onto the Hadean Earth could be a crucial step toward the emergence of the RNA world. I will present results from simulating the formation of these prebiotic organics through the Strecker synthesis and a simplified version of the formose reaction inside carbonaceous chondrite parent bodies. By using an up-to-date thermochemical equilibrium model coupled with a 1D thermodynamic planetesimal model, we calculated the abundances of these molecules within planetesimals of different sizes and heating histories. Different from previous studies, we assumed the initial volatile concentrations more appropriate for the formation zone of carbonaceous chondrite parent bodies. This represents more accurately cosmochemical findings that these bodies have formed inside the inner, ∼2–5 au, warm region of the solar system. We performed laboratory experiments using catalysts present in carbonaceous chondrites to infer the yield of ribose among all pentoses forming during the formose reaction. These laboratory yields were used to tune our theoretical model that can only predict the total abundance of pentoses. We found that the calculated nucleobase (Paschek et al. 2023) and ribose (Paschek et al. 2022) abundances were matching or similar to the ones measured in carbonaceous chondrites. In conclusion, the Strecker synthesis and aqueous formose reaction might produce most of these organics in carbonaceous chondrites. The life-building blocks of the RNA world could be synthesized inside parent bodies and later delivered onto the early Earth.