Sunday, July 29, 2018

Our Uncommon Earth

From Monsignor Charles Pope:
I have written more on these factors (sometimes called “Rare Earth” Hypothesis) here: Earth is a Rare Jewel.    But the essential point of the theory is that there are many factors that have made life possible on earth by providing a stable setting for life to arise and develop. Here are just some of the many:
  1. Earth is at just the right distance from the Sun so that it is warm enough for ice to melt, but not so hot as to boil and steam away. Water is also able, in this habitable zone (the so-called “Goldilocks” region), to both evaporate and condense at lower levels in the atmosphere, thus permitting a more even distribution of water and the cycle of water over dry land known as precipitation.
  2. For suns to spawn Earth-like planets they must have sufficient “metallicity,” which is necessary for the formation of terrestrial rather than gaseous planets.
  3. Earth is in a “habitable zone” within the galaxy as well. Closer to the center of galaxies, radiation and the presence of wandering planetoids make life there unlikely.
  4. Earth exists in a disk-shaped spiral galaxy (the Milky Way) rather than in an elliptical (spheroid) galaxy. Spiral galaxies are thought to be the only type capable of supporting life.
  5. Earth’s orbit around the sun is an almost perfect circle rather than the more common “eccentric” (elongated) ellipse. Steep elliptical orbits take a planet relatively close to and then relatively far from the sun, with great consequences for warmth and light. Earth’s stable, nearly circular orbit around the sun keeps our distance from it relatively constant, and hence the amount of heat and light does not vary tremendously.
  6. Two nearby “gas giants” (Jupiter and Saturn) attract and catch many wandering asteroids and comets and generally keep them from hitting Earth. The asteroid belts also keep a lot of flying rock in a stable orbit and away from us.
  7. Our molten core creates a magnetic field that holds the Van Allen radiation belts in place. These belts protect Earth from the most harmful rays of the sun.
  8. Earth’s volcanism plays a role in generating our atmosphere and in cycling rich minerals widely.
  9. Our sun is just the right kind of star, putting out a fairly steady amount of energy. Other types of stars are more variable in their output and this variance can utterly destroy life or cause it to be unsustainable due to the extremes.
  10. Earth’s fairly rapid rotation reduces the daily variation in temperature. It also makes photosynthesis viable because there is enough sunlight all over the planet.
  11. Earth’s axis is tilted just enough relative to its orbital plane to allow seasonal variations that help complex life, but not so tilted as to make those variations too extreme.
  12. Our moon causes tides that are just strong enough to permit tidal zones (a great breeding ground for diverse life) but not so severe as to destroy life.
It would appear that for complex life to be sustained, many factors must come together in just the right way. (Read more.)
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