The Hot Spring Hypothesis for an Origin of Life

Abstract

We present a testable hypothesis related to an origin of life on land in which fluctuating volcanic hot spring pools play a central role. The hypothesis is based on experimental evidence that lipid-encapsulated polymers can be synthesized by cycles of hydration and dehydration to form protocells. Drawing on metaphors from the bootstrapping of a simple computer operating system, we show how protocells cycling through wet, dry, and moist phases will subject polymers to combinatorial selection and draw structural and catalytic functions out of initially random sequences, including structural stabilization, pore formation, and primitive metabolic activity. We propose that protocells aggregating into a hydrogel in the intermediate moist phase of wet-dry cycles represent a primitive progenote system. Progenote populations can undergo selection and distribution, construct niches in new environments, and enable a sharing network effect that can collectively evolve them into the first microbial communities. Laboratory and field experiments testing the first steps of the scenario are summarized. The scenario is then placed in a geological setting on the early Earth to suggest a plausible pathway from life's origin in chemically optimal freshwater hot spring pools to the emergence of microbial communities tolerant to more extreme conditions in dilute lakes and salty conditions in marine environments. A continuity is observed for biogenesis beginning with simple protocell aggregates, through the transitional form of the progenote, to robust microbial mats that leave the fossil imprints of stromatolites so representative in the rock record. A roadmap to future testing of the hypothesis is presented. We compare the oceanic vent with land-based pool scenarios for an origin of life and explore their implications for subsequent evolution to multicellular life such as plants. We conclude by utilizing the hypothesis to posit where life might also have emerged in habitats such as Mars or Saturn's icy moon Enceladus. Key Words: Origin of life-Prebiotic chemistry-Hydrothermal systems-Protocells-Progenotes-Microbial communities. Astrobiology 20, 429-452. ''To postulate one fortuitously catalyzed reaction, perhaps catalyzed by a metal ion, might be reasonable, but to postulate a suite of them is to appeal to magic.''

A Constructive Way to Think about Different Hydrothermal Environments for the Origins of Life

“…This would help to address the "crucial experiment" established by John Platt regarding the origins of life [34]. Addressing this obstacle would allow us to further develop the hydrothermal vent hypothesis in a fashion like, but not limited to, the hot-spring hypothesis [35][36][37]. Once polymers are shown to be produced in this system further work can address the effects of selection on said polymer species.…”

Impact of Wet-Dry Cycling on the Phase Behavior and Compartmentalization Properties of Complex Coacervates

“…9,15 Despite the likelihood of prebiotic wet-dry cycling and its demonstrated benefits for polymerization reactions, [11][12]16 reports of its impact on molecular self-assembly and compartmentalization have thus far been restricted to lipid vesicles. 17 A study showed that vesicles could survive numerous hydration-dehydration cycles, 18 while others demonstrated that cycling can help in vesicle formation and encapsulation of macromolecules within. [19][20] Membraneless compartments, such as those produced by complex coacervation and other forms of liquid-liquid phase coexistence, are vigorously investigated for their potential in concentrating molecules and assisting reactivity.…”

Getting Beyond the Toy Domain. Meditations on David Deamer’s “Assembling Life”

“…Damer and Deamer, in AL and elsewhere (e.g., [11]) imply that much of this woolly language is analogy or metaphor to illustrate key points, and I afraid that here they push one of my (metaphorical) buttons, because analogies, similies and metaphors make for terrible science. Robbie Burns could sing "My love is like a red, red rose" and not expect his listeners to infer that his belovéd derived her blushing colour from anthocyanins.…”

“…The chapter then goes through the steps, the evidence, and future tests. This has been expanded in [9,11], and in both book…”

“…In my opinion, a vesicle encapsulating random organic molecules is almost as far from life as the bulk "prebiotic soup" from which it was made. To draw "Protocells → Progenote" in a diagram [11] skips over everything about how that transition happens, i.e., how life originates! And again, polymers that stabilize a vesicle are said to have the function of stabilizing the vesicle, but "function" implies contribution to an aggregate goal of the system that is not implicit in its parts (as the function of a shoe is to protect the foot).…”