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Planet Formation: Problems with Water, Carbon, and Air

Thanks to a study from two MIT planetary scientists, the rare planet doctrine now finds additional support.

This is the conclusion that Earth has many unique, apparently designed features that enable it to support life and, in particular, advanced life. The reseachers model degassing during the accretion phase of planetary formation for planets ranging in mass from 1 to 30 times the mass of Earth.1 Their study was motivated in part by the recent discovery of several “super-Earths,” planets outside the solar system ranging in mass from 3 to 10 times Earth’s mass.

These scientists begin by pointing out that planets in general possess three different opportunities for gaining an atmosphere: capture from the protoplanetary disk surrounding their primordial star, degassing during the planetary accretion process, or later degassing resulting from the planet’s tectonic activity. While capture from the protoplanetary disk certainly is the dominant means for the buildup of atmospheres around the gas giant planets, planetary scientists are still uncertain of the degree to which such capture plays a role for planets the size of Earth or a few times larger. Thus, the MIT team decided to consider only the role of degassing during the planetary accretion process.

They based their models on measurements of the bulk compositions in the most primitive meteorites found in the solar system. These ancient remnants of the solar system’s protoplanetary disk represent the material from which Earth formed. They contain up to 20 percent of water by mass. The team used the range of water and carbon found in such meteorites and modeled how much of it would be retained in the formation process by Earths and super-Earths. The scientists determined that degassing during accretion alone would result in water and carbon compounds making up to 20 percent and 5 percent of the mass of Earths and super-Earths, respectively. They found, too, that using even modest estimates of water and carbon in the meteorites resulted in Earths and super-Earths ending up with very deep oceans and very thick atmospheres.

Both results pose major problems for potential habitability. Due to deep oceans, no conceivable amount of plate tectonic activity would ever produce continents. Without continents there would be no possibility for land life. Additionally, many important nutrient-recycling mechanisms would be absent. Thick atmospheres loaded with carbon compounds would trap tremendous amounts of heat, and would result in atmospheric pressures that would make lungs inoperable and block out so much stellar light as to impede photosynthesis.

This study underscores just how anomalous our Earth is. For a planet as large as it is and as far away from its star, Earth is miraculously water- and carbon-poor. Water makes up just 0.02 percent of Earth’s mass; carbon just 0.003 percent. While water and carbon are essential for life, too little or too much proves deadly, especially in the case of advanced life. Earth possesses the just-right amount of each.

Furthermore, the report demonstrates that Earth, like all planets its size and distance from its star, started off with a huge amount of water and carbon. Thanks to an exquisitely designed collision event early in the planet’s history, Earth lost just the right amounts of water and carbon. This event also led to the formation of the Moon.2

The MIT team’s research study illustrates a Christian apologetics principle. It shows that the more we learn about the physics of extrasolar planetary systems, the more evidence we accumulate for the supernatural, super-intelligent design of the Milky Way Galaxy, the solar system, and Earth for the benefit of all life on Earth, both simple and complex.

Other related resources of interest:

10 Breakthroughs of 2010 booklet

Small Extrasolar Water World Discovered” web article





  1. Linda T. Elkins-Tanton and Sara Seager, “Ranges of Atmospheric Mass and Composition of Super-Earth Exoplanets,” Astrophysical Journal 685 (October 1, 2008): 1237-46.
  2. Hugh Ross, Creation as Science (Colorado Springs: NavPress, 2006), 111-15.