  The search for biosignatures on exoplanets connects the fields of biology and
biochemistry to astronomical observation, with the hope that we might detect
evidence of active biological processes on worlds outside the solar system.
Here we focus on a complementary aspect of exoplanet characterisation
connecting astronomy to prebiotic chemistry: the search for molecules
associated with the origin of life, prebiosignatures. Prebiosignature surveys
in planetary atmospheres offer the potential to both constrain the ubiquity of
life in the galaxy and provide important tests of current prebiotic syntheses
outside of the laboratory setting. Here, we quantify the minimum abundance of
identified prebiosignature molecules that would be required for detection by
transmission spectroscopy using JWST. We consider prebiosignatures on five
classes of terrestrial planet: an ocean planet, a volcanic planet, a
post-impact planet, a super-Earth, and an early Earth analogue. Using a novel
modelling and detection test pipeline, with simulated JWST noise, we find the
detection thresholds of hydrogen cyanide (HCN), hydrogen sulfide (H2S),
cyanoacetylene (HC3N), ammonia (NH3), methane (CH4), acetylene (C2H2), sulfur
dioxide (SO2), nitric oxide (NO), formaldehyde (CH2O), and carbon monoxide (CO)
in a variety of low mean molecular weight (<5) atmospheres. We test the
dependence of these detection thresholds on M dwarf target star and the number
of observed transits, finding that a modest number of transits (1-10) are
required to detect prebiosignatures in numerous candidate planets, including
TRAPPIST-1e with a high mean molecular weight atmosphere. We find that the
NIRSpec G395M/H instrument is best suited for detecting most prebiosignatures.
