Some months ago someone (whom I can’t recall) drew my attention to a
distinction between the habitable zone and the abiogenesis zone, and a
paper that makes this distinction, “The origin of
RNA precursors on exoplanets.” The distinction
between the abiogenesis zone—where life can start—and the circumstellar
habitability zone (CHZ)—where life can come to maturity, perhaps in the
form
of a planetary-scale biosphere, has many possibilities, among them that
it can be extended to alternative forms of emergent complexity such as
I have postulated in what I call emergent complexity pluralism, which was the
central idea of my presentation at the IBHA conference in Milan last July.
For each form of emergent
complexity, there could be one set of boundary conditions that holds for the
emergence of this particular emergent complexity, and another set of boundary
conditions that must be present for the expansion, development, and longevity
of that same form of emergent complexity. Now that I think of it (I didn’t put
this in the essay), my hunch is that in some cases, these two sets of
boundary conditions will coincide, while in other cases these two sets will
overlap, and, perhaps yet more rarely, these sets of boundary conditions will
be disjoint.
The only instance of disjoint boundary
conditions (and this marginal at best) that I can think of are the
conditions for the emergence of strong artificial intelligence and the
conditions for the expansion and longevity of strong artificial
intelligence. Some expositions of a possible
post-human “intelligence explosion” imply that humanity is a genetic
condition
for the advent of artificial intelligence, but, once AI begins to expand
explosively, it would benefit from ridding itself of humanity; this
scenario
strikes me as something approximately similar to disjoint conditions for
the
genesis and for the maturity of AI. Part of this formulation, however,
comes down to how we define boundary conditions, since if we put enough
of these conditions into our background assumptions, then only disjoint
conditions—the differentia—will remain in the foreground. In
other words, what we assume and what we do not assume will make a
difference in how we formulate boundary conditions.
Another point to be made here is that the paper cited above,
“The origin of
RNA precursors on exoplanets” (from which the image and caption
below are taken), assumes a particular mechanism for the origins of life
that is dependent upon UV radiation. There are many proposed origin of
life mechanisms, not all of which require a UV flux above a given
threshold. But the power of the distinction between genetic boundary
conditions and maturity boundary conditions is that it is independent of
this particular mechanism. If another origin of life mechanism—say, for
example, the nuclear geyser model—is employed, we might also observe that the boundary conditions for nuclear geysers are likely distinct from from boundary conditions for life spawned by nuclear geysers to thrive. For any given origin of life mechanism, or for any given combination of origin of life mechanisms, there may be abiogenesis boundary conditions distinct from the boundary conditions for the life thus produced to come to maturity in a planetary-scale biosphere.
Indeed, we now have pretty good evidence that the conditions under which life initially appeared on Earth, whatever the mechanism by which it appeared, approximates the conditions that we would today identify as conditions for extremophile life. But for life to have evolved to its present level of complexity, i.e., a planetary-scale biosphere of multi-cellular organisms, life itself changed the conditions of our homeworld to produce an environment that is clement for us and for other biological beings like ourselves, which is a large-scale distinction between conditions of emergence and conditions of maturity.
Fig. 4 Abiogenesis zone. A period-effective temperature diagram of confirmed exoplanets within the liquid water habitable zone (and Earth), taken from a catalog (1, 42, 43), along with the TRAPPIST-1 planets (3) and LHS 1140b (4). The “abiogenesis zone” indicates where the stellar UV flux is large enough to result in a 50% yield of the photochemical product. The red region shows the propagated experimental error. The liquid water habitable zone [from (44, 45)] is also shown.