Editor’s note: Dr. Denton is a biochemist and Senior Fellow with Discovery Institute’s Center for Science & Culture. His work, including his books Evolution: A Theory in Crisis and Nature’s Destiny: How the Laws of Biology Reveal Purpose in the Universe, has had a critical impact on the debate over Darwinian evolution. His thinking will form the subject of an upcoming documentary, Privileged Species.
In his new book, Lucky Planet: Why Earth is Exceptional — and What That Means for Life in the Universe,1 astrobiologist David Waltham presents arguments for believing that rocky planets with stable climatic condition for billions of years and capable of sustaining the evolution of complex life forms may be very rare in the universe. They may be so rare, he writes, that the chances of ever finding another within our galaxy or even within the observable universe are remote. (Waltham’s book was the subject of earlier comments by Casey Luskin; see here.)
Waltham’s argument is based on the notion that the environmental conditions for complex life, including a stable temperature and climate, which he describes in the case of the Earth as being "almost too good to be true,"2 depend on a set of wildly improbable contingencies. These start with our good fortune in having a "Goldilocks Moon" — i.e., a moon with just the right properties to stabilize the Earth’s orbit and axial tilt over billions of years — ensuring that the climate remains bio-friendly over a sufficiently long period of time to allow for the origin and evolution of complex intelligent life forms. As he points out,3 "We must be living on a planet suitable for intelligent life even if such worlds are extraordinarily rare and peculiar." He claims that the only explanation we need to explain our infinite good fortune is anthropic selection or observer bias. And he concludes that given the probably extreme rarity of Goldilocks planets, "We are looking at the most severe case of observational bias in the history of science"4 (my emphasis).
Of course not all researchers agree that habitable worlds will be as rare as Waltham argues. For an example of the contrary view, which is probably the majority view among astrophysicists, see James Kasting’s excellent How to Find a Habitable Planet.5But even if we accept for the sake of argument his notion that Lucky Earths are fantastically rare, dependent on a vastly improbable chain of unique contingent cosmical and planetary events "which got us through the past four billion years by the skin of our teeth"; even if we accept his postulate of their necessity for intelligent observers to evolve (but see caveat below), they are in themselves not sufficient. It is only because of an extraordinary non-contingent bio-fitness in the main constituents of the atmosphere and hydrosphere that the four-billion-year saga turned out so successfully. The fact is that the day-to-day, month-to-month, year-to-year, eon-to-eon constancy in the Earth’s mean temperature and climatic constancy has a very great deal to do with the non-contingent fitness of many of the core constituents that make up the Earth’s hydrosphere and atmosphere.
Water is the prime example. Unless the various physical and chemical properties of water (particularly its thermal properties) were almost exactly as they are, there would be no Hadley cells, trade winds, oceanic currents6; no transfer of heat from the tropics to higher latitude to moderate the climate in both the tropics and the higher latitudes; no thermohaline circulation to mix and refresh the oceans7; no cold trap to prevent the loss of hydrogen to space and the consequent evaporation of the oceans8; no water cycle to erode and recycle (in conjunction with the tectonic cycle) the minerals of the hydrosphere and crust, refreshing and maintaining the elemental constancy of the world’s oceans. No matter how fortuitous the Earth-Moon system or the configuration of the solar system, without the extraordinary fitness of the thermal and other physical properties of water — its viscosity, solvation properties and so forth — no rocky planet anywhere in the cosmos, no matter how "lucky," would be capable of sustaining a carbon-based biosphere.9
Stick just with the fitness of water for the tectonic system, a system without which we would certainly not be here and whose intricate design and fitness for life as it exists on Earth is critically dependent on the properties of water in so many ways. As Marcia Bornjerud comments on the tectonic system in her book Reading the Rocks10:
All parts of the fabrication and recycling process are cleverly linked and powered largely by water. The destruction of ocean crust via subduction leads to the formation of continental crust through water-facilitated melting. The destruction of continental crust via water-driven erosion ultimately replenishes the mantle for the next round of ocean crust production. Efficient, sustainable, robust, and elegant, the system would win top honors in an industrial design competition. [My emphasis.]
Earth’s unrivalled stability and clemency can be attributed to the ways in which the planet maintains communication and exchange between its interior and exterior. And in almost every one of these transactions, water is involved as emissary, diplomat, shipper, or provocateur.
Moreover it is not just the material properties of water that must be almost exactly as they are if the tectonic machine is to function. The properties of all the other major constituents of the Earth’s crustal rocks must also be almost exactly what they are.12
And for warm-blooded, air-breathing (oxygen-utilizing) beings such as ourselves, there are other non-contingent elements of fitness that have made possible our thriving on planet Earth and that are genuine universals. There is the cooling effect of the evaporation of water, the attenuation of the reactivity of oxygen at ambient temperatures, the fact that the gases of the atmosphere let through just the right light for photosynthesis and the generation of oxygen while at the same time absorbing all the harmful EM radiation on either side of the visual window. Commenting on the narrowness of this crucial window, the Encyclopaedia Britannica remarks13: "Considering the importance of visible sunlight for all aspects of terrestrial life, one cannot help being awed by the dramatically narrow window in the atmospheric absorption…and in the absorption spectrum of water" (my emphasis).
Whatever role good fortune (contingent events such as acquiring a Goldilocks Moon) may have played in conferring long-term climatic stability on our home planet, there is not the slightest element of contingency in the unique bio-fitness of the chemical and physical properties of the constituents of rocky planets, which have also played a critical role in climatic stability and without which we would certainly not be here. Nor is there the slightest contingency in those elements of bio-fitness that underlie our own existence as advanced air-breathing intelligent observers. These non-contingent elements of fitness are genuine universals and will work their magic on any Earth-like planet throughout the cosmos. They give every impression of design for life and have nothing to do with observer bias.14
(1) Waltham, David. Lucky Planet: Why Earth Is Exceptional — and What That Means for Life in the Universe. New York: Basic Books, 2014.
(2) Ibid, p 1.
(3) Ibid, p 4.
(4) Ibid, p 4.
(5) Kasting, James F. How to Find a Habitable Planet. Science Essentials Series. Princeton, N.J: Princeton University Press, 2010.
(6) Vallis, Geoffrey K. Climate and the Oceans. Princeton Primers in Climate. Princeton: Princeton University Press, 2012. See Chapters 5 and 6. For more on the Hadley cell, see Wikipedia’s entry.
(7) Vallis, op cit. Chapter 4.
(8) Wallace, John M. and Hobbs PV. Atmospheric Science: An Introductory Survey. 2nd ed. International Geophysics Series v. 92. Amsterdam; Boston: Elsevier Academic Press, 2006. p. 11.
Lenton, Tim and Watson AJ Revolutions That Made the Earth. Oxford, New York: Oxford University Press, 2011. pp. 67-68
(9) Baross, J.A., S.A. Benner, et al. The Limits of Organic Life in Planetary Systems. Washington, D.C.: National Academies Press, 2007.
(10) Bjornerud, Marcia. Reading the Rocks: The Autobiography of the Earth. Cambridge, MA: Westview Press, 2005. pp. 130-131.
(11) Ibid, p 113.
(12) Ibid, p 119.
(13) Encyclopaedia Britannica, 15th ed. (1994), vol. 18, p. 203.
(14) Unless one extends observer bias to explaining the bio-fitness of the properties of matter such as water to the conception of the multiverse. See Rees, Martin J. Just Six Numbers: The Deep Forces That Shape the Universe. New York: Basic Books, 2000.
Image: Earthrise Revisited/Wikipedia.