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From page 309... ... 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 likeli hood of life elsewhere? Astrobiology is a holistic field of research into the origin, evolution, and distribution of life in the universe.1 As such, planetary science and astrobiology encompass a continuous spectrum spanning the multidisciplinarity of life and physical sciences and investigate the codependence and coevolution of life and the environment. Read the entire page →
From page 310... ... 310 ORIGINS, WORLDS, AND LIFE TABLE 12-1 Extremophiles Nomenclature and Ranges Low → Higha pH Hyperacidophile Acidophile Neutrophile (pH 5–9) Alkaliphile (.pH 9) Read the entire page →
From page 311... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 311 FIGURE 12-1 Generalized model of biogeochemical cycling of energy and essential elements (CHNOPS) on Earth. Read the entire page →
From page 312... ... 312 ORIGINS, WORLDS, AND LIFE Q9.1a How Was the Emergence and Evolution of Life on Earth Influenced by Volatiles, Impacts, and Planetary Evolution in Early Solar System Environments? What were the principal components of the early solar system environment and how did controls on these components (such as available volatile inventory, volatile delivery via impacts and comets, and compositional changes in response to large impacts and planetary evolution) Read the entire page →
From page 313... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 313 molecules in chemical and biological systems. These approaches, which form the basis of systems chemistry and systems biology, can enhance our knowledge of abiotic synthetic routes to the building blocks of life and to possible pathways that the earliest forms of life on Earth, or life elsewhere, might have adopted. Read the entire page →
From page 314... ... 314 ORIGINS, WORLDS, AND LIFE FIGURE 12-2 Question 9. Order of prebiotic and origin of life events (left) Read the entire page →
From page 315... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 315 FIGURE 12-3 Universal phylogenetic trees over the past 30 years. Read the entire page →
From page 316... ... 316 ORIGINS, WORLDS, AND LIFE Q9.1f What Does the Last Universal Common Ancestor (LUCA) Represent (e.g., a Single Individual, a Species, or a Population of Species) Read the entire page →
From page 317... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 317 FIGURE 12-4 Representative idealized cross section of Earth's crust showing the diversity of so-called extreme habitable environments and their approximate location. SOURCE: Merino et al. Read the entire page →
From page 318... ... 318 ORIGINS, WORLDS, AND LIFE FIGURE 12-5 Microscopic images of life at environmental extremes on Earth, including (a) a fungal-prokaryote colony in vesicular basalt, Koko Seamount, Pacific Ocean, 67.5 m below the seafloor; (b) Read the entire page →
From page 319... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 319 energy released through organisms' metabolic functions, as chemicals react back toward equilibrium (see Figure 12-1; NASEM 2019a) Read the entire page →
From page 320... ... 320 ORIGINS, WORLDS, AND LIFE to adapt to poly-extremes. Laboratory and modeling studies, along with research in Earth environments, allow us to probe the fringes of this multi-dimensional space, and the effect on biological potential. Read the entire page →
From page 321... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 321 latter providing critical endmembers likely to be applicable to the search for life off-Earth (Onstott et al. Read the entire page →
From page 322... ... 322 ORIGINS, WORLDS, AND LIFE FIGURE 12-6 Plot using submarine vent data from the mid-ocean ridges in the Atlantic Ocean and Caribbean Sea to illustrate how the cumulative energy theoretically available from water–rock interactions for chemolithotrophic microbial metabolism is subject to multilateral co-variability. Key parameters include physical conditions under which water and rocks react in the subsurface (shown = pressure, temperature; not shown = flow rate) Read the entire page →
From page 323... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 323 create energy sources (e.g., methane and molecular hydrogen) to support life (Schrenk et al. Read the entire page →
From page 324... ... 324 ORIGINS, WORLDS, AND LIFE Processes such as transport, flux, preservation, degradation, concentration, and dilution can modify and impact the distribution and activity of life in the subsurface, and habitable niches may be ephemeral or isolated (Lin et al. 2006; Lollar et al. Read the entire page →
From page 325... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 325 FIGURE 12-7 Biosignature features and measurements ranging in strength of evidence and ease of measurement. Clockwise from top: Structural preferences in organic molecules (nonrandom and enhancing function) Read the entire page →
From page 326... ... 326 ORIGINS, WORLDS, AND LIFE FIGURE 12-8 Decision tree describing the biosignature potential of a given environment (terrestrial or nonterran) in terms of measurable properties that might result in the environment being associated with detectable probable biosignatures that can be confidently ascribed to biology and have a high probability of preservation, along with those environmental properties that might result in a higher probability of false positive or false negative detections. Read the entire page →
From page 327... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 327 In the coming decade, biosignature research needs to include a concerted effort to better understand abiosignatures (i.e., a signature of abiotic processes and phenomena) , in particular those that may mimic biosignatures (see also Question 11) Read the entire page →
From page 328... ... 328 ORIGINS, WORLDS, AND LIFE Strategic Research for Q9.4 • Assess how the essential traits of Earth life, such as metabolism or bioenergetics, arose from the geochemical environment through theoretical, field, and laboratory studies of the connectivity and stoichiometry of metabolic networks, and the geological availability of exploitable redox gradients. • Develop a comprehensive framework for biosignature categories of Earth life to guide the understanding of what biosignatures will be prevalent in life through community-level dialog and consensus, supported by laboratory/experimental and modeling/theoretical research as well as field work on environmentally relevant biosignature classes as well as abiosignatures. Read the entire page →
From page 329... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 329 TABLE 12-2 Biosignature Reliability, Detectability, and Preservation Vary with Time in the Geologic Record Biosignature Type Reported Geochemistry/ Organic Age (Ma) Isotope Mineralogy Morphology Carbon Lipid Forms Formation Type (location) Read the entire page →
From page 330... ... 330 ORIGINS, WORLDS, AND LIFE Q9.5b Which Biosignatures Are Most Likely to Survive in the Environment, and at What Timescales of Preservation? The timescales and mechanisms of survivability make up a core research area that includes the survivability of a modern biosignature against processes that would act to destroy it as it forms; the survivability of a fossil biosignature against geological forces such as weathering, diagenesis, influx of brines or groundwaters; and metamorphism, and/or the survivability of abiosignatures (inherently the study of the relative rates of abiotic and biological, and potentially cryptic, processes) Read the entire page →
From page 331... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 331 et al. Read the entire page →
From page 332... ... 332 ORIGINS, WORLDS, AND LIFE Chan, M.A., N.W. Hinman, S.L. Read the entire page →
From page 333... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 333 Furnes, H., K Muehlenbachs, T Read the entire page →
From page 335... ... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 335 NASEM (National Academies of Sciences, Engineering, and Medicine) Read the entire page →
From page 336... ... 336 ORIGINS, WORLDS, AND LIFE Spinks, S.C., J Parnell, and S.A. Read the entire page →
From page 338... ... Q10 PLATE: A composite image of Saturn's moons, Enceladus (foreground) and Titan (background) Read the entire page →

From page 309...

... 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 likeli hood of life elsewhere? Astrobiology is a holistic field of research into the origin, evolution, and distribution of life in the universe.1 As such, planetary science and astrobiology encompass a continuous spectrum spanning the multidisciplinarity of life and physical sciences and investigate the codependence and coevolution of life and the environment.