  There is growing evidence that brown dwarfs may be comparable to
main-sequence stars in terms of their abundance. In this paper, we explore the
prospects for the existence of life on Earth-like planets around brown dwarfs.
We consider the following factors: (i) the length of time that planets can
exist in the temporally shifting habitable zone, (ii) the minimum photon fluxes
necessary for oxygenic photosynthesis, and (iii) the lower limits on the fluxes
of ultraviolet radiation to drive prebiotic reactions ostensibly necessary for
the origin of life. By taking these effects into consideration, we find that it
is unlikely for brown dwarfs with masses $\lesssim 30 M_J$ to host habitable
planets over geologically significant timescales. We also briefly discuss some
of the major biosignatures that might arise on these planets, assess the
likelihood of their detection, and highlight some avenues for further study.
