III. Ecosmos: A Revolutionary Fertile, Habitable, Solar-Bioplanet, Incubator Lifescape

I. Our EarthMost Distinction: A Rarest Planetary Confluence of Life in Person Favorable Conditions

Spohn, Tilman. Special Issue: Planetary Evolution and Life. Planetary and Space Science. 98/1, 2014. An introduction to this edition with six co-editors including Helmut Lammer and Frances Westall as we Earthlings began our near and far cosmic census of habitable ecobiospheres. With this home world as a measure, the 21st century project going forward involves quantifying an array of features such as core composition, geochemistry, outgasings, atmospheres, mantle hydration, and much more. See for example herein Plate Tectonics on Rocky Exoplanets, Earth-Like Habitats in Planetary Systems, and Biotic vs. Abiotic Earth. But an inkling seems to carry through the papers that this precious animate orb looks increasingly special and maybe unique.

Stern, Robert and Taras Gerya. The importance of continents, oceans and plate tectonics for the evolution of complex life: implications for finding e. Nature Scientific Reports. 14/8552, 2024. A UT Dallas Earth system scientist and an ETU Zurich geochemist make a latest strong case that our past billion years of drifting surface forms with a general land/sea ratio of 30/70 ratio is especially conducive for a life’s developmental emergence and also seems to be a rarest habitable planet occasion.

Within astronomical and biological parameters, the Drake Equation predicts that there should be many exoplanets in our galaxy with active communicative civilizations (ACCs). This optimism, however, is not supported by evidence, often referred to as the Fermi Paradox. Here, we elaborate on the importance of planetary tectonics for biological evolution by adding two additional terms to the Drake Equation: foc (the fraction of habitable exoplanets with continents and oceans) and fpt (the fraction of habitable exoplanets with continents and oceans that have had plate tectonics operating for at least 0.5 Ga). We propose that an absence of ACCs reflects the scarcity of continents and oceans on exoplanets with primitive life. (Excerpt)

Stern, Robert J.. Is Plate Tectonics Needed to Evolve Technological Species on Exoplanets? Geoscience Frontiers. 7/4, 2016. The UT Dallas geoscientist states a thorough case why a long term, global surface condition of relatively balanced, mobile land and ocean ratios is a vital necessity for life to make it all the way from single cells to a sapient species able to learn this and begin to look outward. See also Stagnant Lid Tectonics: Perspectives from Silicate Planets, Dwarf Planets, Large Moons, and Large Asteroids by the author in this journal (9/2, 2018).

Stern, Robert J.. The Evolution of Plate Tectonics. Philosophical Transactions of the Royal Society A. Vol.376/Iss.2132, 2018. Plate tectonics is a very unusual convective style for a silicate planet. All other active silicate bodies are encased in a single lithospheric lid. (17). In a Earth Dynamics and the Development of Plate Tectonics issue, the UT Dallas geoscientist reconstructs ancient crustal comings and goings in graphic stages of asthenosphere and lithosphere convections and subductions. Comparisons are made to single lid Venus and Mars, along with Europa and Io moons. Only Earth has a mobile, “fragmented” mantle, which then has major influences on animal evolution. Amongst the 15 papers are Magma Oceans as a Critical Stage in Tectonics, Biogeodynamics, and Geological Archive of Plate Tectonics. A century after its discovery by Alfred Wegener (1880-1930), the edition achieves a comprehensive noosphere verification. See also Biogeodynamics: Bridging the Gap between Surface and Deep Earth Processes by Aubrey Zerkle in this collection.

To understand how plate tectonics became Earth's dominant mode of convection, we need to address three related problems. (i) What was Earth's tectonic regime before the present episode of plate tectonics began? (ii) Given the preceding tectonic regime, how did plate tectonics become established? (iii) When did the present episode of plate tectonics begin? The tripartite nature of the problem complicates solving it, but, when we have all three answers, the requisite consilience will provide greater confidence than if we only focus on the long-standing question of when did plate tectonics begin? Earth probably experienced episodes of magma ocean, heat-pipe, and increasingly sluggish single lid magmatotectonism. A Neoproterozoic transition (~1,000 to 540 mya) from single lid to plate tectonics also explains kimberlite ages, the Neoproterozoic climate crisis and the Neoproterozoic acceleration of evolution. (Abstract excerpt)

Stevens, Adam, et al. Observational Signatures of Self-Destructive Civilizations. International Journal of Astrobiology. Online October, 2015. Since Earth life seems threatened by nuclear annihilation, bioterrorism, planetary pollution, asteroids, runaway technology, and much more, British astrophysicists including Duncan Forgan contend that extraterrestrial intelligent civilizations will likewise be prone to “total planetary destruction.” Somewhat akin to Jason Wright, et al herein about signs of astroengineering, since this might be an inevitable demise, the archaeological detection of their remains could help answer the issue of the prevalence or absence of other lifekind.

We address the possibility that intelligent civilizations that destroy themselves could present signatures observable by humanity. Placing limits on the number of self-destroyed civilizations in the Milky Way has strong implications for the final three terms in Drake's Equation, and would allow us to identify which classes of solution to Fermi's Paradox fit with the evidence (or lack thereof). Using the Earth as an example, we consider a variety of scenarios in which humans could extinguish their own technological civilization. Each scenario presents some form of observable signature that could be probed by astronomical campaigns to detect and characterize extrasolar planetary systems. Some observables are unlikely to be detected at interstellar distances, but some scenarios are likely to produce significant changes in atmospheric composition that could be detected serendipitously with next-generation telescopes. (Abstract)

Stevenson, David. Planetary Diversity. Physics Today. April, 2004. An introduction to a special issue on why the scientific study of how planets form has come into recent prominence. Foremost is the ability to detect by observation and inference the presence of many extrasolar planets, along with a growing understanding of extraterrestrial geology and atmospheres. From these advances a wider definition of what constitutes a planetary object has occurred. Stevenson goes on to imagine that a Darwinian selection might apply whereby planetary accretion by angular momentum seeks out all possible solar orbital niches. In this view, only a precious few such our Earth might become fertile with sentient life.

Stevenson, David S.. Planetary Mass, Vegetation Height and Climate. International Journal of Astrobiology. Online January, 2019. The British biologist (search) continues his unique studies so as to add another factor that would affect the relative habitability of an Earth to super-Earth size planet. As the Abstract says, a preferred, optimum arboreal height is a necessity for floral and faunal life to devolve and develop.

The maximum height trees can grow on Earth is around 122–130 meters. The height is constrained by two factors: the availability of water, and where water is not limiting, the pressure available to drive the column of water along the xylem vessels against the pull of gravity. In turn the height of trees impacts the biodiversity of the environment in a number of ways. On Earth the largest trees are found in the maritime temperate Pacific Northwest coasts of northern California and southern Oregon. These forests provide many secondary habitats for species and serve as moisture pumps that return significant volumes of water to the lower atmosphere. In this work, we apply mathematical rules to show how super-terran planets will have significantly smaller trees, with concomitant effects on the habitability of the planet. (Abstract)

Stojkovic, neda, et al. Habitability of Galaxies and Application of Merger Trees in Astrobiology. arXiv:1908.05935. University of Belgrade astrophysicists NS, Branislav Vukotic and Milan Cirkovic (search) advance a latest, extensive consideration of how relatively conducive might myriad galactic neighborhoods be for living, evolutionary systems. Their studies draw upon mathematic and geometrics method as described Exploring the Cosmic Evolution of Habitability with Galaxy Merger Trees by Elizabeth Stanway, et al in the Monthly Notices of the Royal Astronomical Society (475/2, 2018).

Galaxies represent the main form of organization of matter in our universe. Here we present a systematic attempt to list and categorize major causal factors playing a role in an emergent galactic habitability. We argue that the methodology of cosmological merger trees can be useful in delineating what are systematic and lawful astrobiological properties of galaxies at the present epoch vs. those which are due to historical contingency. In a sense, this approach is directly complementary to using large-scale cosmological simulations to study habitable zones of individual galaxies with high mass/spatial resolution. Altogether, these endeavors serve to advance a new era of synergy and synthesis between cosmology and astrobiology. (Abstract edit)

Synder-Beattie, Andrew, et al. The Timing of Evolutionary Transitions Suggests Intelligent Life is Rare. Astrobiology. November, 2020. Oxford University, Mathematical Ecology Research Group and Future of Humanity Institute scholars including Anders Sandberg point out one more check-point for emergent life, mind and selves to cope with and pass through. They argue that these nested stages from earliest rudiments to aware sentience are dauntingly difficult. For an array of reasons they appear to be prohibitive filters. So another barrier is erected on the way to our possible EarthMost fitness.

It is unknown how abundant extraterrestrial life is, or whether such life might be complex or intelligent. On Earth, the emergence of complex intelligence required a series of evolutionary transitions such as abiogenesis, eukaryogenesis, sexual reproduction, and multicellularity. Some of these transitions could have been extraordinarily improbable, even in conducive environments. Using a Bayesian model we demonstrate that expected transition times likely exceed the lifetime of Earth. Arriving at the opposite conclusion would require very conservative priors, evidence for earlier transitions, multiple instances, and more. Our study provides an initial basis to evaluate how biological assumptions and fossil record data impact the probability of evolving intelligent life. (Abstract excerpt)

Tegmark, Max. We're Not Insignificant After All. www.edge.org. In this response to the 2007 Edge question: "What Are You Optimistic About," the MIT cosmologist offers a most positive vista whereby conscious, informed living entities might be able to expand into and transform the future universe. Human beings may be a rarity but yet possess such a potential to influence the fate of cosmic destiny. Indeed, as the quote avers, the next century could decide whether this path is taken. Here is a diametric alternative to the moribund physical multiverse whereof people are of no account. Our hope for this website is to document welling support for this grand option, to wit therefore choose life and earth.

Moreover, this brief century of ours is arguably the most significant one in the history of our universe: the one when its meaningful future gets decided. We'll have the technology to either self-destruct or to seed our cosmos with life. The situation is so unstable that I doubt that we can dwell at this fork in the road for more than another century. If we end up going the life route rather than the death route, then in a distant future, our cosmos will be teeming with life that all traces back to what we do here and now. I have no idea how we'll be thought of, but I'm sure that we won't be remembered as insignificant.

Tinetti, Giovanna, et al. The EChO Science Case. arXiv:1502.05747. With some 350 authors and 50 pages, this is a manifesto for an Exoplanet Classification Observatory project over the next decade as a scientific survey of a grand new genesis universe that fills itself with stars and planets so that an intelligent species can achieve its own self-comprehension. A sample of diverse subjects might be: exoplanet core to atmospheric composition, how many large gaseous planets, what is the range of planetary spin, orbit shape, dynamic movement, and can planets around low mass stars keep their atmospheres. And akin to the views of Elke Pilat-Lohinger above, a significant finding is just being realized. Our own solar system which contains a bioplanet able to do this is not typical at all, and especially conducive due to its long term stability. Whatever to make of this?

EChO has been conceived to address the following fundamental questions:• Why are exoplanets as they are? • What are the causes for the observed diversity? • Can their formation and evolution in history be traced back from their current composition? EChO would provide spectroscopic information on the atmospheres of a large, select sample of exoplanets allowing the composition, temperature, size and variability to be determined at a level never previously attempted. This information can be used to address a wide range of key scientific questions relative to exoplanets: • What are they made of? • Do they have an atmosphere? • What is the energy budget? • How were they formed? • How do they evolve? • How do weather conditions vary with time? And of course: • Do any of the planets observed have habitable conditions?

Conclusion: Our knowledge of planets other than the eight “classical” Solar System bodies is in its infancy. We have discovered over a thousand planets orbiting stars other than our own, and yet we know little or nothing about their chemistry, formation and evolution. Planetary science therefore stands at the threshold of a revolution in our knowledge and understanding of our place in the Universe: just how special are the Earth and our Solar System? It is only by undertaking a comprehensive chemical survey of the exoplanet zoo that we will answer this critical question.

Tobin, John, et al. Astro2020 Science White Paper: The Formation and Evolution of Multiple Star Systems. arXiv:1904.08442. A project proposal by 16 astronomers from across the USA to study these stellar duplexes because “nearly half of Solar-type stars are have been found to lie in binary or higher-order multiple systems.” An inference, one might add, is that such common pairing would be another obstacle for a long-term habitability.

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