KLD6
Keynote (EXOA): Kinetic Windows for RNA Evolution on Rocky Worlds
Co-organized by EXOA
Conveners:
Giovanni Poggiali,
Stavro Lambrov Ivanovski
Abstract
Life on Earth emerged within a narrow time window delimited by the cessation of late accretion bombardment on the one hand, and evidence gleaned from molecular phylogenetic studies, isotopic biosignatures and morphological traces on the other. Molecular clock analyses place the median age for the Last Universal Common Ancestor (LUCA) population of all contemporary DNA life at ca. 4.2 Ga. Cryptic isotopic biosignatures go back as far as 4.1± 0.01 Ga in Hadean zircons (δ¹³C = -24 ± 5‰) and more robustly in Eoarchean rocks at ca. 3.83 Ga (δ¹³C ≈ -35‰). Morphological remains including microfossils and microbially mediated sedimentary structures are almost as ancient (ca. 3.5 Ga). Here, I parameterize the kinetic windows for abiogenesis and show that before the LUCA, a postulated RiboNucleic Acid (RNA) and/or RiboNucleoProtein (RNP) World persisted for less than ~130 Myr. Earth’s kinetic windows stand out compared to other worlds in our Solar System and provide a guide for searching for biospheres on rocky worlds around other stars: sustained stable liquid water from ca. 4.4 Ga, wet-dry cycling under an atmosphere, effective crustal recycling to rejuvenate disequilibrium chemistry, available key elements for chemistry, mechanisms to concentrate prebiotic reaction products, and sufficient spatial scales for geochemical and proto-biochemical evolution. I also argue that the emergence of the RNA World and its subsequent evolution required organic precursors coordinated with environmental conditions in time with each transition – from prebiotic chemistry to cellular life – governed by distinct rate-limiting processes operating over 10⁵–10⁸ year timescales.