Factoring Origin of Life Hypotheses into the Search for Life in the Solar System and Beyond

Abstract

Two widely-cited alternative hypotheses propose geological localities and biochemical mechanisms for life’s origins. The first states that chemical energy available in submarine hydrothermal vents supported the formation of organic compounds and initiated primitive metabolic pathways which became incorporated in the earliest cells; the second proposes that protocells self-assembled from exogenous and geothermally-delivered monomers in freshwater hot springs. These alternative hypotheses are relevant to the fossil record of early life on Earth, and can be factored into the search for life elsewhere in the Solar System. This review summarizes the evidence supporting and challenging these hypotheses, and considers their implications for the search for life on various habitable worlds. It will discuss the relative probability that life could have emerged in environments on early Mars, on the icy moons of Jupiter and Saturn, and also the degree to which prebiotic chemistry could have advanced on Titan. These environments will be compared to ancient and modern terrestrial analogs to assess their habitability and biopreservation potential. Origins of life approaches can guide the biosignature detection strategies of the next generation of planetary science missions, which could in turn advance one or both of the leading alternative abiogenesis hypotheses.

Formation of Thiophene under Simulated Volcanic Hydrothermal Conditions on Earth—Implications for Early Life on Extraterrestrial Planets?

“…According to recent literature [ 7 , 36 ], thiophenes per se should not be named biomarkers, due to their possible abiotic origin, but the presence of thiophenes, as easily detectable molecules, could indicate samples or sites, which should be investigated in more detail for the presence of additional organic molecules like amino acids or fatty acids. It is also suggested that terrestrial origin-of-life conditions could be used as a guideline in the search for life on extraterrestrial planets [ 37 ].…”

Origin of Life: The Point of No Return

“…Another scenario describes lipid lamellae on the earth's surface with the potential to trap polymers (e.g., short RNA and peptides) undergoing a selection process accompanied by dry/wet cycles. The assumption of the gradual emergence of Darwinian evolution within multiple networks of lipid vesicles based on polymer interactions is presented as the next step but again, no mechanism is provided [2,23]. Lipid vesicles or lamellae may sustain integrity, but positive feedback from the vesicle structure to an information source capable of determining the synthesis of the same stable lipid vesicles is unspecified.…”

“…In searching for the first living cell, at some moment, a proto-cell(s) capable of evolving should emerge. The newly established proto-cell must have a relatively simple structure with heredity and a primordial metabolism [1,2]. However, the process leading to the formation of a proto-cell must consist of a multi-step process that begins with the precursors of nucleic acids, peptides, lipids, and energy followed by polymer interactions and enzymatic metabolic reactions.…”

“…However, the process leading to the formation of a proto-cell must consist of a multi-step process that begins with the precursors of nucleic acids, peptides, lipids, and energy followed by polymer interactions and enzymatic metabolic reactions. Based on our understanding of evolution, we can picture a scenario where multiple variants of proto-cells initially emerged but most adapted, survived, and evolved as the Last Universal Common Ancestor (LUCA) [2,3]. An obvious question is "What are the critical steps for living matter to emerge?"…”

To What Inanimate Matter Are We Most Closely Related and Does the Origin of Life Harbor Meaning?

“…This generates a hybrid between a pond and a vent, relying on UV light as an energy source like Oparin and Haldane did at a time before anyone knew how cells conserve energy or grow. The hot spring hypothesis [107][108][109] goes back to the warm little pond, with the settings changed in that the pond is fed by hydrothermal springs (providing thermal energy and wet-dry cycles with first molecules possibly coming from meteorites). There is no chemical role for the vent in the hot spring narrative, it just supplies water and salts, nor is there a connection to the lifestyle of the first cells.…”