  We study the spectrum of a planetary atmosphere to derive detectable features
in low resolution of different global geochemical cycles on exoplanets - using
the sulphur cycle as our example. We derive low resolution detectable features
for first generation space- and ground- based telescopes as a first step in
comparative planetology. We assume that the surfaces and atmospheres of
terrestrial exoplanets (Earth-like and super-Earths) will most often be
dominated by a specific geochemical cycle. Here we concentrate on the sulphur
cycle driven by outgassing of SO2 and H2S followed by their transformation to
other sulphur-bearing species which is clearly distinguishable from the carbon
cycle which is driven by outgassing of CO2. Due to increased volcanism, the
sulphur cycle is potentially the dominant global geochemical cycle on dry
super-Earths with active tectonics. We calculate planetary emission, reflection
and transmission spectrum from 0.4 to 40 micrometer with high and low
resolution to assess detectable features using current and Archean Earth models
with varying SO2 and H2S concentrations to explore reducing and oxidizing
habitable environments on rocky planets. We find specific spectral signatures
that are observable with low resolution in a planetary atmosphere with high SO2
and H2S concentration. Therefore first generation space and ground based
telescopes can test our understanding of geochemical cycles on rocky planets
and potentially distinguish planetary environments dominated by the carbon and
sulphur cycle.
