Dust evolution, a global view: IV. Tying up a few loose ends

This work is an attempt to tie together some of the, seemingly disparate, loose ends from the preceding papers in this series into the global view of dust evolution in the interstellar medium. In particular, the nature of the hydro-carbonaceous, infrared absorption and emission band carriers is discussed within the context of a simple poly- hexa-cyclic molecular view. The sequence of interstellar dust mantle accretion and grain- grain coagulation into aggregates, and their consequences for the interstellar dust size distribution, extinction and dust thermal emission, is explored. The effects of accretion and coagulation on the interstellar gas-to-dust ratio in the Milky Way and in distant galaxies are estimated. The importance of interstellar grain-surface epoxide species is re-visited and the likely and consequent connection between dense interstellar cloud dust and cometary dust explored. A possible connection between and the origin of the suite of interstellar OCN-containing molecules, and their interesting chemistry, is discussed. Finally, pathways to amino acid formation and their likelihood as a universal basis for life everywhere in the universe is speculated upon.