Towards a ladder of cosmic habitability

Earth is a part of the solar system located on the fringes of the Milky Way, one of the (roughly) 200 billion galaxies that exist in the Universe. Given the existence of life here on Earth, some inevitable questions are, “Are we alone in the vastness of the cosmos? Is the habitability of Earth run-of-the-mill or a cosmic anomaly? When and how did the earth become habitable?” These questions lie at the very heart of the field of astrobiology. The requirements for habitability are generally summed up in three main quantities: (i) the presence of metals (elements heavier than hydrogen) required to assemble "terrestrial" (earth-like) planets; (ii) the presence of a nearby star for light and energy and; (iii) the lack of any "deleterious" radiation from nearby sources such as exploding massive stars (supernovae), black holes or explosions producing enormous amounts of gamma rays (gamma ray bursts). The YAG interdisciplinary PhD offers a unique opportunity to really synergise astrophysics and biology to make progress in this field. The idea would be to build a ladder of habitability (from stellar to galactic to cosmological scales) accounting for crucial "missing" ingredients such as:
● reformulating the notion of "habitability" accounting for evolutionary biology. This requires defining what “life” is, inspired by but not restricted to life as we know it from evolutionary history and current biology on Earth, before detailing critical environmental conditions for “habitability”
● accounting for the (currently ignored) different timescales involved in galaxy formation, planet formation, planetary cooling, formation of an atmosphere (if this is deemed relevant), cell formation and formation of other prerequisites for life including mechanisms of self replication and deleterious radiation source formation/explosion.