  Biomolecules can be synthesized in interstellar ice grains subject to UV
radiation and cosmic rays. I show that on time scales of $\gtrsim 10^{6}$
years, these processes lead to the formation of large percolation clusters of
organic molecules. Some of these clusters would have ended up on proto-planets
where large, loosely bound aggregates of clusters (superclusters) would have
formed. The interior regions of such superclusters provided for chemical
micro-environments that are filtered versions of the outside environment. I
argue that models for abiogenesis are more likely to work when considered
inside such micro-environments. As the supercluster breaks up, biochemical
systems in such micro-environments gradually become subject to a less filtered
environment, allowing them to get adapted to the more complex outside
environment. A particular system originating from a particular location on some
supercluster would have been the first to get adapted to the raw outside
environment and survive there, thereby becoming the first microbe. A collision
of a microbe-containing proto-planet with the Moon could have led to fragments
veering off back into space, microbes in small fragments would have been able
to survive a subsequent impact with the Earth.
