Enceladus: First Observed Primordial Soup Could Arbitrate Origin-of-Life Debate

Abstract

A recent breakthrough publication has reported complex organic molecules in the plumes emanating from the subglacial water ocean of Saturn's moon Enceladus (Postberg et al., 2018, Nature 558:564–568). Based on detailed chemical scrutiny, the authors invoke primordial or endogenously synthesized carbon-rich monomers (<200 u) and polymers (up to 8000 u). This appears to represent the first reported extraterrestrial organics-rich water body, a conceivable milieu for early steps in life's origin (“prebiotic soup”). One may ask which origin-of-life scenario appears more consistent with the reported molecular configurations on Enceladus. The observed monomeric organics are carbon-rich unsaturated molecules, vastly different from present-day metabolites, amino acids, and nucleotide bases, but quite chemically akin to simple lipids. The organic polymers are proposed to resemble terrestrial insoluble kerogens and humic substances, as well as refractory organic macromolecules found in carbonaceous chondritic meteorites. The authors posit that such polymers, upon long-term hydrous interactions, might break down to micelle-forming amphiphiles. In support of this, published detailed analyses of the Murchison chondrite are dominated by an immense diversity of likely amphiphilic monomers. Our specific quantitative model for compositionally reproducing lipid micelles is amphiphile-based and benefits from a pronounced organic diversity. It thus contrasts with other origin models, which require the presence of very specific building blocks and are expected to be hindered by excess of irrelevant compounds. Thus, the Enceladus finds support the possibility of a pre-RNA Lipid World scenario for life's origin.

Protobiotic Systems Chemistry Analyzed by Molecular Dynamics

“…Among the strengths of the GARD model are its realistic depiction of the emergence of life-like entities from a prebiotic mixture of random chemicals [100], and its capacity to underlie a concrete molecular basis for molecular dynamics simulations. The foregoing roadmap is intended to indicate some of the possible computer experiments that could attempt to confirm the dynamic non-equilibrium features of the GARD model, which underlie the emergence of lipid-based compositional replicators.…”

Protobiotic Systems Chemistry Analyzed by Molecular Dynamics

“…Among the strengths of the GARD model are its realistic depiction of the emergence of life-like entities from a prebiotic mixture of random chemicals [96], and its capacity to underlie a concrete equilibrium features of the GARD model, which underlie the emergence of lipid-based compositional replicators. This should enhance the model's realism, whereby rather than being based on statistically-derived catalytic properties, the newly simulated GARD will be grounded in bona fide atomically-detailed molecules.…”

Polyesters as a Model System for Building Primitive Biologies from Non-Biological Prebiotic Chemistry

“…Most of these classes are dominated by compounds not used in present-day biology [18]. In light of this, it seems plausible that a similarly complex compound suite was provided to primitive Earth (or existed on another planet [19]) from one or more sources (e.g., [20][21][22]), and indeed various prebiotic chemistry simulations similarly produce a complex array of organic products ( Figure 2) [23]. In fact, the number and diversity of compounds in the Murchison meteorite can only be crudely estimated due to analytical challenges [13], suggesting that the actual organic complexity may be far greater.…”

“…A notional example of such "chemical opportunism" is the emergent systemic autocatalysis proposed by [30]. The idea that the first autocatalytic chemical systems could have been composed of non-biomolecules has also been proposed by Lancet and coworkers [19,29]. More nuanced examples of primitive non-biomolecular systems, include those incorporating purely in vitro-produced polymers (themselves produced from biomolecular components such as amino acids) which do not participate in modern biology, have also been explored including self-assemblies of lipid-like peptides [31].…”