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VII. Pedia Sapiens: A Genesis Future on Earth and in the Heavens

C. An Earthropic Principle: Novel Evidence About a Special Planet

Waltham, Dave and Lewis Dartnell. Is the Earth Special? Astronomy & Geophysics. Vol. 53, August, 2012. A report on a Royal Astronomical Society, and Astrobiological Society of Britain, December 2011, conference by this title. In light of the recent exoplanet findings and other research studies, a 21st century universe seems graced by a propensity to fill (seed) itself with solar systems and potential bioplanets. With Jim Kasting and Helmut Lammer as keynoters, a stellar array such as Monica Grady, Nick Lane, and Richard Nelson scanned the range of cosmic and evolutionary causes and contingencies in search of an answer. If an early consensus might be entered, unicellular microbes are likely to be widespread. But many steps over a billion year planetary life span, such as plate tectonics and a good moon, are required to reach sentient, intelligent beings (as if a cosmos trying to gain its own vision and voice) which serves to distinguish our precious orb. So (great) Earth may indeed be an extraordinary occasion in the galactic heavens.

Recent developments in cosmology suggest an unimaginably vast `multiverse' generated by the process of cosmological inflation. According to ideas from fundamental physics, such as string theory, in such a vast space physical laws themselves may vary from region to region. In at least some cases, theories may allow a probabilistic determination of cosmological parameters (in the same way one might attempt to determine the probability distribution for the number of planets orbiting a typical star). However, such probabilities, and hence the properties of our region of the Universe, may be strongly preconditioned by our own existence as observers. As an example, these arguments --- sometimes referred to as the anthropic string landscape --- currently provide the most compelling explanation for the Universe's observed acceleration. The same ideas may have implications in assessing the likelihood of intelligent life on other planets. (Andrew Liddle “Special Earth, Special Universe?”)

Complex and intelligent life has arisen late in the history of the Earth, towards the end of the period that it will be habitable by complex organisms. I have argued that this is consistent with such life being contingent on a sequence of intrinsically unlikely events, and that we can even be quantitative about some aspects of these events. We’d conclude that the universe is very sparsely populated with such life, but this is not primarily due to the rarity of postulated astronomical Goldilocks factors. Rather it is due to the fact that an unlikely sequence of coupled biological and whole-system evolutionary steps must occur on a planet for it host the transition from basic chemistry through to conscious beings, as has happened here on Earth. (Andrew Watson “Goldilocks: Biology or Astronomy?”)

The Fermi Paradox refers to the non-detection of extraterrestrial intelligence (ETI), and in particular the apparent non-intereference with the Earth's biosphere by ETI over Earth's history. The 'Rare Earth Hypothesis' is a popular solution to the Fermi Paradox because, if the Earth is uniquely special as an abode of life, ETI will necessarily be rare (or even non-existent). However, while accepting that the Fermi Paradox very likely does indicate that ETI are rare in the Galaxy, I shall argue that this is unlikely to be due to unique properties of the Earth as a planet. Rather, even if Earth-like planets are common (which seems increasingly likely), I shall argue that intelligent life is probably rare owing to the low probability of either the origin of life itself or, more likely, of key evolutionary events (such as endosymbiosis in the origin of eukaryotic cells) which have occurred here but which may not happen even on essentially identical planets. In other words, I shall argue that the abundance (and probable rarity) of intelligent life in the universe depends more on the quirks of evolutionary biology than uniquely favourable astronomical or planetary conditions. (Ian Crawford “Does the Fermi Paradox Imply that the Earth is Special?”)

Waltham, David. Half a Billion Years of Good Weather: Gaia or Good Luck? Astronomy & Geophysics. 48/3, 2007. Earth’s climate over the past 550 million years of the Phanerozoic era of “visible animal life” has been an order of magnitude more stable than previous eons. A University of London geologist finds such consistency in accord with a biosphere that maintains atmospheric conditions favorable to its flora and fauna. A large Moon and a gap between Jupiter and Saturn further contribute to a preferential “anthropic” milieu. In an expanded cosmic perspective then, the human imperative not to upset this conducive global environment becomes even more critical.

Perhaps most importantly of all, this discovery would imply that climate stability is far from inevitable and that human-induced (or other) climate change could be far more dramatic and damaging than we have previously believed. (26)

Waltham, David. Lucky Planet: Why Earth is Exceptional – and What That Means for Life in the Universe. New York: Basic Books, 2014. The University of London astrobiologist and geologist contends that our relatively stable biosphere climate over a billion years is why we are here to witness. But such a stretch of benign weather is so improbable as to make it statistically unique. By one man’s analysis and opinion, no other neighbors are out there, this Earth is it. But could we just as well proffer that Earth is a “Plucky Planet” whereupon innate Gaian feedback processes have served to regulate, and life’s cooperative intelligence has keep evolution on an ascendant course?

As we discover countless exoplanets orbiting other stars, we become ever more hopeful that we may come across extraterrestrial life. Yet even as we become aware of the vast numbers of planets outside our solar system, it has also become clear that Earth is exceptional. In Lucky Planet, astrobiologist David Waltham argues that Earth’s climate stability is one of the primary factors that makes it able to support life, and that nothing short of luck made such conditions possible. Describing the three factors that typically control a planet’s average temperature—the heat received from its star, how much heat the planet absorbs, and the concentration of greenhouse gases in the atmosphere — Waltham paints a complex picture of how special Earth’s climate really is. Citing factors such as the size of our Moon and the effect of an ever-warming Sun, Waltham challenges the prevailing scientific consensus that other Earth-like planets have natural stabilizing mechanisms that allow life to flourish. (Publisher excerpts)

Waltham, David. Star Masses and Star-Planet Distances for Earth-like Habitability. Astrobiology. 17/1, 2017. The Royal Holloway University of London exoplanet researcher and author of Lucky Planet: Why Earth is Exceptional (2014) discusses current studies about how conducive stellar types and solar systems may or may not be conducive for life to originate, inhabit and evolve.

Wang, Haiyang, et al. The Volatility Trend of Protosolar and Terrestrial Elemental Abundances. arXiv:1810.12741. Australian National University, Canberra astrophysicists including Charles Lineweaver provide a detailed quantification of stellar and planetary chemical affinities via dynamic out-gassings over the ages of solar system evolution. See also Enhanced Constraints on the Interior Composition and Structure of Terrestrial Exoplanets by this group at arXiv:1810.04615 In regard, still another variable is involved with the relative habitability of a candidate exoEarth.

We present new estimates of protosolar elemental abundances based on an improved combination of solar photospheric abundances and CI chondritic abundances. These new estimates indicate CI chondrites and solar abundances are consistent for 60 elements. We compare our new protosolar abundances with our recent estimates of bulk Earth composition, thereby quantifying the devolatilization in going from the solar nebula to the formation of the Earth. (Abstract)

To first order, Earth is a devolatilized piece of the solar nebula. Similarly, rocky exoplanets are usually devolatilized pieces of the stellar nebulae out of which they and their host stars formed. If this is correct, we can estimate the chemical composition of rocky exoplanets by measuring the elemental abundances of their host stars, and then applying a devolatilization algorithm. The main goal of this paper is to go beyond the usual comparison of the silicate Earth with CI chondrites. We do this by comparing the bulk elemental abundances of Earth and Sun, and thus calibrate this potentially universal process associated with the formation of terrestrial planets. (1)

Watson, Andrew. Gaia and Observer Self-selection. Schneider, Stephen, et al, eds. Scientists Debate Gaia. Cambridge: MIT Press, 2004. Some thoughts on a “biological anthropic principle” whereof only conducive planets that evolve complex sentient beings can achieve their own intelligent discovery and self-recognition.

Webb, Stephen. If the Universe is Teeming with Aliens-- Where is Everybody? New York: Springer, 2015. The entry is a second, award-winning edition of the British physicist’s 2002 volume with the same Fermi paradox title. Since huge advances have been made since, especially about myriad exoplanets, 25 more possible answers have been added to the original 50 as to why amongst billions of galaxies, each with billions of solar systems, there are as yet no overt signs of extraterrestrial civilizations. The work is also seen as an update to Rare Earth (2003) by Peter Ward and Donald Brownlee whence celestial, geologic, and evolutionary stages that need to happen or be passed through (Lineweaver) pile up even more, such as just the right degree of asteroid impacts.

While an argument has long been the immense number of chances, by this further winnowing out (Morbidelli, Pliat-Lohinger, Tinetti, et al, herein) an auspicious resolve may begin to dawn upon us. The new additions are in a long chapter that sums up the author’s conclusion – They Don’t Exist! Here is an awesome 2010s finding as Earth’s evolution and history enters a critical phase of emergent personsphere self-sapience, of intentional peaceable sustainability or runaway nuclear, ecological devastation, indeed much a cosmic and planetary self-selection of Kinder or cinder.

Weinberger, Alycia. Building Planets in Disks of Chaos. Sky & Telescope. November 13, 2008. Reviewed in the Exoearths section, this article by a Carnegie Institution of Washington, DC astronomer is also noted here, along with “Planetary Peculiarities” by Ken Croswell in the September S. & T., “Are Super-Sized Earths the New Frontier” by Ray Jayawardhana in the November 2008 Astronomy, and other such postings, because the latest celestial research conveys how stochastic and variable are the occasions, orbits and kinds of myriad terrestrial worlds. We human beings have the rarest of opportunities to therefore choose Earth as a fruitful abode of future, peaceful, sustainable, life and mind, a child of the expectant cosmos.

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