During my late teens some friends entered me in a dance endurance contest. Unbeknownst to me, they laid bets about how long I could go before my pace would slow down. Long after I’d worn out five dance partners and won the contest, they asked me if I was starting to tire. When I answered that I felt the same as when the contest first started I earned the nickname “Dynamo.”
The moniker may have said more about my friends’ knowledge of physics than it did about my level of physical fitness. As every physicist knows, dynamos do wear out. Earth’s dynamo, however, seems exceptional. It’s run for billions of years, with no sign of winding down. Thanks to this strong and enduring dynamo, life—advanced life in particular—is possible on Earth’s surface. The magnetic field generated by Earth’s dynamo prevents solar radiation from sputtering away the planetary atmosphere (see figure 1). That same magnetic field establishes Van Allen Belts (see figure 2) that shield Earth’s life from devastation by cosmic rays.
A team of researchers from the University of Hawaii and the University of California at Berkeley developed a detailed model to ascertain how permanent dynamos would be on rocky planets of varying masses and distances from their host stars.1 The four scientists proved the worth of their model by successfully reproducing the properties of both Earth’s and Venus’ interior and magnetic field. With Venus, for example, the team demonstrated that the planet’s dehydrated, high-viscosity mantle demonstrated that Venus’ dynamo either shut down very early in its geological history or never operated at all.
The team aimed to apply their model to the kinds of rocky planets astronomers should soon discover in large numbers. Their model predicted that, at a fixed planet mass, the bigger the planet’s core, the longer lived is the planet’s dynamo and the stronger its magnetic field. The model also showed that the higher a planet’s mantle viscosity, the briefer is its dynamo history. Likewise, the higher the thermal conductivity of the planet’s core the briefer the dynamo history. Other factors they found that affect a planet’s dynamo history included the thermal expansivity of the core, the initial core temperature, and the heat flow across the core-mantle boundary.
The model established that rocky planets larger than 3.0 Earth-masses will not develop inner cores and, consequently, will possess either very weak dynamos or no dynamos at all. Planets between 2.0 and 3.0 Earth-masses will lack solid inner cores and, thus, fail to produce long-lived dynamos. Likewise, planets lacking mobile lids—that is, plate tectonics—and planets lacking an interior structure consisting of both a silicate mantle and a near pure iron core will also fail to produce long-lasting dynamos.
Through their research, the four scientists working on this model added to the weight of the rare-Earth doctrine’s evidence. This doctrine states that while planets the size and mass of Earth may prove to be abundant, planets with the just-right characteristics and physical and chemical composition to enable the support of advanced life will prove either rare or non-existent.
The researchers showed that the advanced life requirements for a planet with a long-lasting dynamo demands:
- a fine-tuned mass
- a fine-tuned core mass
- a fine-tuned set of mobile lids
- a fine-tuned mantle viscosity
- a fine-tuned ratio of the solid inner core radius compared to the liquid outer core radius
- a fine-tuned core thermal conductivity
- a fine-tuned core thermal expansivity
- a fine-tuned rate of heat flow across the core-mantle boundary
- a fine-tuned initial core temperature
- a fine-tuned inner core composition
- a fine-tuned outer core composition
The sum total of such precision defies any conceivable naturalistic explanation. This much fine-tuning is consistent only with the Bible’s message that God supernaturally designed Earth, its planetary partners, and its life for the specific benefit of human beings.
- Eric Gaidos et al., “Thermodynamic Limits on Magnetodynamos in Rocky Exoplanets,” Astrophysical Journal 718 (August 1, 2010): 596–609.