Astrobiologists have used the term for many decades. This shell encompasses the distance at which a planet in a fairly circular orbit could maintain liquid water on its surface.
Mathematician Granville Sewell has argued in these pages that evolutionary theory is at crosscurrents with the second law of thermodynamics (the law of entropy), dooming it to failure.
Bill Nye, among others, has speculated that "We May Discover Life on Europa."
With the landing of a probe on comet 67P, excitement has centered on the idea that life arose in water carried here by comets.
At best, closely examining a comet may illustrate a scenario whereby organic molecules were delivered to our planet, or to another.