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Planet Habitability Requires a Lifetime of Fine-Tuning

In my youth I would frequently backpack to remote mountains. For a trip lasting only two days I would pack just a tarp and some twine. For a trip lasting more than a week I needed a tent with sealed seams, a large rain fly, and an entryway. Just as longer tent habitability requires much more design, according to several teams of astronomers the same is true for planet habitability.

Up until now, astrobiologists (scientists who investigate the possible existence of living organisms on planets other than Earth) have limited their research efforts to determining what planetary features are necessary for habitability. Short-lived habitability can sustain only microorganisms. For advanced life to be possible, a planet must be able to sustain habitable conditions for several billion years.

Three astronomers from Arizona State University demonstrated that the abundance ratios of several elements—carbon, sodium, magnesium, and especially oxygen—relative to iron in a planet’s host star dramatically impact the planet’s potential habitability lifetime.1 For example, only a star with an oxygen-to-iron ratio as high as the Sun’s will remain in a sufficiently stable burning mode for a long-enough time that advanced life on a planet orbiting it becomes feasible.

This requirement supports the “rare Sun” doctrine. While astronomers have found a few planet-bearing solar-type stars with oxygen-to-iron ratios the same as the Sun’s, their discoveries yield no evidence for stars that––like the Sun––have remained in a stable burning mode for at least four billion years.

A star’s elemental composition also affects its rocky planets’ mineralogy. A second research team, an Australian-British-American combination, showed that a star with an elemental composition different from the Sun’s will fail to produce a planet with the kind of atmosphere and geochemical cycles necessary to sustain life for billions of years.2

A third group of three American astronomers pointed out that unless the solar system’s primordial planets were exposed to a certain kind of supernova (exploding star) where the latter stages of r-process nucleosynthesis was efficiently expressed, Earth would seriously lack rare-earth elements (lanthanides––fifteen metallic chemical elements, plus scandium and yttrium).3 It is the relatively high abundance of these seventeen elements in Earth’s crust that makes high-technology civilization possible.

Without enduring, strong plate tectonic activity the nutrient recycling necessary for long-standing life and for the feasibility of advanced life is impossible, as affirmed by yet a fourth team of researchers, two American astronomers from Rice and Harvard Universities. They published a paper explaining that long-lasting, strong plate tectonics requires delicate fine-tuning of a planet’s (1) size, (2) internal energy content, (3) distance from its host star, (4) crustal rock strength, (5) viscosity, (6) thermal conductivity, (7) surface liquid water properties, and (8) a host of different properties of its mantle and core. Such plate tectonics also requires significant constraints on the planet’s geologic and climatic histories.4 This long list of fine-tuning design prerequisites implies that planets capable of possibly sustaining advanced life must be very rare indeed.

A fifth research effort by three other American astronomers established that a long habitability lifetime requires enduring, continuous, aggressive silicate (rocks comprising 95 percent of Earth’s crust) weathering.5 Erosion of exposed silicates through rainfall is the only means by which enough greenhouse gases can be removed from a planet’s atmosphere to adequately compensate for the host star’s increasing luminosity (brightness). Such erosion is possible only if a planet has both surface continents and oceans.

A complicating factor is that the silicate erosion rate must increase with time. Different kinds and quantities of surface life either speed up or slow down silicate erosion rates. Consequently, another requirement for advanced life is for the planet to possess precisely the right kinds, quantities, and diversities of life on its surface at different times for billions of years. These factors allow the planet’s atmospheric greenhouse gas quantity to remain continuously at varying just-right levels while optimal variation yields planetary surface temperatures ideal for life.

Astrobiologists define habitable planets as bodies with the necessary features for surface liquid water to be possible. In truth, even primitive life needs many, many more fine-tuned planetary features.6 Advanced life requires the previous existence of several billions of years of primitive life. These five studies establish that habitability lifetimes in the billions of years demand such a long list of exceptionally fine-tuned planetary characteristics as to defy naturalistic explanations. It seems reasonable to identify a Fine-Tuner: “The earth is the Lord’s and everything in it.”

  1. Patrick A. Young, Kelley Liebst, and Michael Pagano, “The Impact of Stellar Abundance Variations on Stellar Habitable Zone Evolution,” Astrophysical Journal Letters 755 (August 20, 2012): L31.
  2. J. C. Bond et al., “Beyond the Iron Peak: r- and s-Process Elemental Abundances in Stars with Planets,” Astrophysical Journal 682 (August 1, 2008): 1234–47.
  3. Matthew R. Mumpower, G. C. McLaughlin, and Rebecca Surman, “The Rare Earth Peak: An Overlooked r-Process Diagnostic,” Astrophysical Journal 752 (June 20, 2012): 117.
  4. A. Lenardic and J. W. Crowley, “On the Notion of Well-Defined Tectonic Regimes for Terrestrial Planets in this Solar System and Others,” Astrophysical Journal 755 (August 20, 2012): 132.
  5. Dorian S. Abbot, Nicolas B. Cowan, and Fred J. Ciesla, “Indication of Insensitivity of Planetary Weathering Behavior and Habitable Zone to Surface Land Fraction,” Astrophysical Journal 756 (September 10, 2012): 178.
  6. Hugh Ross, RTB Design Compendium (2009)