Reasons to Believe

Volcanism and Plate Tectonics on Earthlike Planets

At long last astronomers are recognizing that their quest to find a life-friendly, earthlike planet will not be fulfilled simply by discovering a planet approximating the mass of Earth that orbits its star at a distance that would permit surface liquid water to exist.

For advanced life to be possible, the planet's surface must possess both landmasses and oceans. Both features must cover a large fraction of the planet's surface (see here) and must do so continuously for hundreds of millions of years. These requirements demand a finely tuned and highly stable level of plate tectonic activity.1

A team of planetary scientists at the University of California, Berkeley and the University of Hawaii have studied yet another example of fine-tuning required for a planet to possibly sustain advanced life: the need to ensure that volcanism, with respect to time over the history of planet, is maintained at the just-right levels.2 In their analysis of the geodynamics of planets approximating the mass of Earth, the team determined that plate tectonics physics and chemistry must be carefully fine-tuned to guarantee that the needed continents, oceans, and levels of volcanism are sustained for long enough periods of time.

Just-right continent building and volcanism are critical ingredients for bringing about changes in Earth's atmosphere and surface so as to adequately compensate for changes in the Sun's luminosity—the problem of the faint Sun paradox.3 Degassing from volcanic activity helps with this vital compensation by bringing about changes in the chemistry of Earth's atmosphere.

The researchers used thermal evolution models "to explore the dependence of convection-driven decompression mantle melting on planet mass."4 Their analysis uncovered several problems for earthlike planets more massive than Earth. First, they found that a planet's crust gets thicker as its mass increases. When a crust gets too thick, crustal plates, if any develop, are less likely to slip past or under one another (subduction). Good plate movement is necessary to recycle nutrients, rebuild eroded continents, and remove greenhouse gases from the atmosphere. A too-thick crust also decreases the amount of a planet's volcanic activity. Too little volcanic activity lowers the flux of important minerals to the planet's surface and the flux of gases to the atmosphere.

Second, the team found that plate tectonics, if it does develop on planets more massive than Earth, is more likely to shut down sooner. Strong plate tectonic activity that has persisted for more than four billion years is one reason why Earth can sustain advanced life.

Third, the team discovered that planets more massive than Earth will produce a lot more buoyant crust. Too much buoyant crust would eliminate the possibility of subduction. No subduction implies no plate tectonics.

The researchers' models also demonstrated that even if a planet maintains strong plate tectonic activity for billions of years it does not guarantee that the planet can support advanced life. They pointed out that in many cases volatiles (gases) generated by volcanic activity would never reach the planet's surface. The volatiles could be trapped in magma melts that are so dense that they sink to the bottom of the planet's mantle.

A second problem arises if the planet's atmospheric pressure is too great. If the pressure of the volcanic volatiles is less than that of the atmosphere, they will never be released into the atmosphere. This issue is far from trivial. Earth possesses an atmosphere that is only one percent as dense as planetary formation models would predict. Thanks to a highly fine-tuned collision event early in its history with a Mars-sized planet, Earth lost virtually all its primordial atmosphere.5

Our planet's abnormally thin atmosphere permitted Earth to release the volcanic volatiles and, thus, made possible a continuous and abundant presence of life for the past 3.8 billion years. For example, without volcanic volatiles releases Earth would have become permanently sterilized due to unending snowball events. It goes without saying that the release of too great of a quantity of volcanic volatiles would prove deadly for advanced life also. Both the quantity and kind of volcanic volatiles released into the atmosphere must be fine-tuned.

The planetary science research team did not write specifically about the fine-tuning design of Earth for the benefit of advanced life. However, their analysis did reveal that although plate tectonic activity is a necessary ingredient for advanced life, they must manifest features that planet formation models predict would rarely occur. Likewise, while the release of volcanic volatiles into a planet's atmosphere is a requirement for advanced life, planet formation models predict that the needed amounts and kinds of volatiles released into the atmosphere would rarely occur. As seen through this research, the more we learn about all planetary systems and planetary formation, the more evidences we find for the supernatural, super-intelligent design of Earth, its star, and its accompanying planets for the benefit of life.

Subjects: Extrasolar Planets, Solar System Design

Dr. Hugh Ross

Reasons to Believe emerged from my passion to research, develop, and proclaim the most powerful new reasons to believe in Christ as Creator, Lord, and Savior and to use those new reasons to reach people for Christ. Read more about Dr. Hugh Ross.

References:

  1. Hugh Ross, More Than a Theory (Grand Rapids: Baker, 2009), 152-64.
  2. E. S. Kite, M. Manga, and E. Gaidos, "Geodynamics and Rate of Volcanism on Massive Earth-Like Planets," Astrophysical Journal 700 (August 1, 2009): 1732-49.
  3. Ross, 153-62.
  4. E. S. Kite, M. Manga, and E. Gados: 1732.
  5. Ross, 135-37.