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Re-emergence of life after catastrophic extinction event
(Chen & Benton 2012) |
Many times we hear about habitability or the habitability zones within stellar exoplanetary systems which is closely related to the presence of liquid water as a precursor to life. However, to have the heavier elemental components making up planets much like our Solar System required generations of stellar evolution to create those elements in the abundances we measure today. If we make the assumption that life evolves in a similar environment, then there is a dependence on the age, evolution and position of an exoplanetary system in a galaxy--or, put another way, a galactic habitable zone (GHZ) (e.g.,
Lineweaver et al. 2004,
Dosovic et al. 2019).
Another way to think of GHZs is to assess the components within a galaxy that could hinder or damage the formation of life on an exoplanet. For example, an exoplanetary system being too close to a number of supernovae or where the star formation rate is high creating gamma rays, X-rays and cosmic rays could strip atmospheres of UV blocking. Also, complex life seems to require complex heavy elements which implies that the location of the exoplanetary system in a galaxy would need to lie somewhere in the very narrow 'young thin disc' (how narrow? see
Yoachim & Dalcanton 2006). This is the region where star formation and evolution is most active and produces the heavier elements through supernova explosions.
One hopeful component for habitability in general is that life seems robust. On Earth, for example, life rebounded quickly after catastrophic events or within millions or tens of millions of years (e.g. see
Chen & Benton 2012) which is only approximately 1 to 5% of the age of the planet. Given that, any life on exoplanets would have the ability to rebound and evolve to some form of intelligence over 10x within a habitable galactic zone once critical local habitability conditions for life were established.
