  The chemical environments of young planets are assumed to be largely
influenced by impacts of bodies lingering on unstable trajectories after the
dissolution of the protoplanetary disk. We explore the chemical consequences of
impacts within the context of reducing planetary atmospheres dominated by
carbon monoxide, methane and molecular nitrogen. A terawatt high-power laser
was selected in order to simulate the airglow plasma and blast wave surrounding
the impactor. The chemical results of these experiments are then applied to a
theoretical atmospheric model. The impact simulation results in substantial
volume mixing ratios within the reactor of 5% hydrogen cyanide (HCN), 8%
acetylene (C$_2$H$_2$), 5% cyanoacetylene (HC$_3$N) and 1% ammonia (NH$_3$).
These yields are combined with estimated impact rates for the Early Earth to
predict surface boundary conditions for an atmospheric model. We show that
impacts might have served as sources of energy that would have led to
steady-state surface quantities of 0.4% C$_2$H$_2$, 400 ppm HCN and 40 ppm
NH$_3$. We provide simulated transit spectra for an Earth-like exoplanet with
this reducing atmosphere during and shortly after eras of intense impacts. We
predict that acetylene is as observable as other molecular features on
exoplanets with reducing atmospheres that have recently gone through their own
`Heavy Bombardments', with prominent features at 3.05 $\mu$m and 10.5 $\mu$m.
