Origins, Worlds, and Life A Decadal Strategy for Planetary Science and Astrobiology 2023-2032 (2022) / Chapter Skim
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12 Question 9: Insights from Terrestrial Life What conditions and processes led to the emergence and evolution of life on Earth, what is the range of possible metabolisms in the surface, subsurface and/or atmosphere, and how can this inform our understanding of the likelihood of life elsewhere? Astrobiology is a holistic field of research into the origin, evolution, distribution, and distribution of life in the universe.
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There is an extensive literature (and debate) about the major milestones in the history of Earth and the history of life, the nature of the earliest life as discerned from fossils and chemical signatures, and the pathways and timing for the evolution of life and for key metabolisms (Betts et al.
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The diversity of terrestrial life, and its plasticity to respond to different levels of nutrient and energy availability, transport and flux, inform the detectability of biospheres that might exist in habitable environments beyond Earth. Insights gained from the biochemistry, structure and physiology of terrestrial organisms, and how they have evolved through deep time, are the basis to develop comprehensive frameworks to search for evidence of life on other worlds.
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bombardment, gave rise to the dynamic, diverse, and interconnected environments from which the chemistry that led to life's origins arose (NASEM 2019 and references therein)
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it has been demonstrated that even organic carbon with "light" carbon isotope values requires careful contextual investigation of the microstructure of minerals and fracture infillings between and across those mineral boundaries to determine the abiotic versus biotic nature of macromolecular carbon (Ménez et al.
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FIGURE 12.2 Question 9. Order of prebiotic and origin of life events, and approximate timing of major transitions in the history of the biosphere.
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FIGURE 12.3 Question 9. Universal phylogenetic trees over the last 30 years.
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Strategic Research for Q9.1 ● Characterize the surface and subsurface processes (e.g., impactor flux, atmospheric conditions, volcanism, tectonism) and the range of chemical inventories (e.g., volatiles, organics)
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FIGURE 12.4 Question 9. Representative idealized cross section of Earth's crust showing the diversity of so-called "extreme" habitable environments and their approximate location.
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As a result, biological potential in different environments can also vary significantly. At the high end of the spectrum, light-dependent ecosystems can support large amounts of biomass recycled in short periods of time.
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Q9.2b How Does the Biological Potential (i.e., Abundance, Productivity, Diversity) of Light Dependent Ecosystems Compare to That of Light-Independent Ones?
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Q9.2d How and When Did Viruses Originate and What Role Have They Played, and Continue to Play, in the Evolution of Life on Earth? Viruses are key contributors to Earth's ecosystems, but there is much yet unknown regarding their influence on cellular life, their role in evolutionary history, their physical interactions with the Earth system, and their persistence and decay under various environmental conditions (Figure 12.5)
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of subsurface habitats on Earth is one of the most readily actionable strategies to address questions about the processes governing habitability and the nature, diversity, and preservation of both extant and extinct subsurface communities on Earth and other worlds (see also Question 10)
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as well as the rate at which reactants are mined from the system. In parallel, the bulk composition and mineralogy of the host rock influences which key chemical species are removed from or enriched in the circulating fluid relative to the original source fluid.
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surface biosphere (Onstott et al. 2019 and references therein)
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Q9.3d How Does the Biological Potential of Life Vary in the Subsurface, How Much of the Total Planetary Biomass Is Represented by Subsurface Communities, and What Are the Mechanisms for Life's Dispersal and Transport Within and Out of the Subsurface? The total volume of subsurface habitats on Earth is immense, but life is heterogeneously distributed, and the biological potential (abundance, productivity, diversity, and others)
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comes from not only the probability of life having produced it, but also from the improbability of nonbiological processes producing it (NASEM 2019 and references therein)
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FIGURE 12.8 Question 9. Decision tree describing the biosignature potential of a given environment (terrestrial or non-terran)
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sub-units or atomic ratios, systematic isotopic ordering at molecular and intramolecular levels, and uneven distribution patterns (e.g., carbon number, concentration, δ13C) of structurally related compounds (Summons et al.
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and energy flux, can affect these latter two criteria of survivability (metabolic and biosynthetic rates) and detectability (rates of destruction and attrition of biosignatures)
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is perhaps the most well-known example of an environment suppressing the rise of a biosignature. The exact timing of oxygenic photosynthesis and the detection of O2 in Earth's atmosphere remains controversial (Lyons et al.
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detection in geological samples older than 1 million years highly problematic (NASEM 2019)
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Strategic Research for Q9.5 ● Assess the ways in which physical and chemical processes in Earth's habitable environments affect biosignature and abiosignature detectability and whether those processes favor the detection of certain biosignatures over others using field, laboratory, theoretical and remote sensing approaches designed to investigate the rates of biosignature production and destruction and rates of physical and chemical processes. ● Investigate the processes and environmental conditions on Earth that are most likely to result in the preservation of biosignatures with field studies of biosignature preservation in relevant planetary environments and laboratory studies of the alteration of proposed biosignatures under planetary environmental conditions.
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Chan, M.A., N.W. Hinman, S.L.
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Hoehler, T
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McDermott, J.M., J.S. Seewald, C.R.
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Shock, E.L.
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Q10 PLATE: A composite image of Saturn's moons, Enceladus (foreground) and Titan (background)
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