"A review of habitable zones—for animals as well as microbes, and in the galaxy and Universe as well as around our sun—leads to an inescapable conclusion: Earth is a rare place indeed"(RE:33).
Posted: July 20, 2005
Last Updated: October 1, 2005
'Rare Earth Factors':
Habitat for complex life. Liquid water near surface. Far enough to avoid tidal lock.
Long enough lifetime. Not too much ultraviolet.
Retain atmosphere and ocean. Enough heat for plate tectonics. Solid/molten core.
CO2-silicate thermostat. Build up land mass. Enhance biotic diversity. Enable magnetic field.
Clear out comets and asteroids. Not too close, not too far.
Right distance. Stabilizes tilt.
Seasons not too severe.
Enough for life. Not enough for Runaway Greenhouse.
Invention of photosynthesis. Not too much or too little. Evolves at the right time.
Not in center, edge or halo.
Maintenance of adequate temperature, composition and pressure for plants and animals.
Few giant impacts. No global sterilizing impacts after an initial period.
Snowball Earth. Cambrian explosion. Inertial interchange event.
Enough heavy elements. Not small, elliptical, or irregular" (RE:xxxi-xxxii).