Darwin first postulated - 145 years ago - that life might have originated in “…some warm little pond with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc. present, that a protein compound was chemically formed, ready to undergo still more complex changes…”. However, the 1970’s discovery of deep sea black smokers and their rich vent fauna, together with evidence from the mitochondrial tree of life, led to the currently prevailing view that life got started at deep sea vents. But it turns out that the energy required for polymerisation of organic molecules from simple amino acids comes from expelling a water molecule. In addition, the cytoplasm of cells from all three branches of life have K+/Na+ ratios more aligned with fresh water than seawater, and that certain key elements (B, Zn, Mn) required as catalysts for polymerisation are hard to concentrate in the uniform marine reservoir. Thus, it turns out that the oceans, or any permanently wet environment, are
not suitable for prebiotic chemistry and thus a land-based environment undergoing wet-dry cycles is required for an Origin of Life setting. But what kind of environment? Previous authors have suggested a desert with seasonal rain, or a river flowing over komatiitic crust as possible sites for the Origin of Life. But these cold-water environments lack the capacity for compositional complexity and highly reactive interfaces. Recent discoveries from an ancient analogue site in Western Australia’s Pilbara region provide support for an Origin of Life in terrestrial hot springs. The 3.48 Ga Dresser Formation is well known as hosting some of Earth’s oldest convincing evidence of life (stromatolites, fractionated stable isotopes, and putative microbial remains), all within an active volcanic caldera characterised by voluminous hydrothermal fluid circulation. Previously, the depositional environment was considered as shallow marine, but the recent discovery of geyserite and other siliceous sinter deposits containing biosignatures and spatially closely associated with stromatolites, point to a thriving terrestrial hot spring setting with wet-dry cycles. A parallel, key, discovery is of concentrations of the critical elements required for prebiotic chemistry (B, Zn, and Mn), which arise from hot water-rock interactions. These discoveries are leading to a developing model for the Origin of Life in terrestrial hot spring fields, and have implications for Astrobiology and the search for life elsewhere in the Solar System. On Mars, we advocate for the Columbia Hills site that has known hotspring deposits identified from a previous rover mission. Further afield, advocates for exploration of the icy water moons of Saturn and Jupiter face the problem of a permanently wet environment that appears not to be favourable for life to develop.
[mehr]
