Title: Spectra of Earth-like Planets Through Geological Evolution Around FGKM Stars,
Abstract: Future observations of terrestrial exoplanet atmospheres will occur for
planets at different stages of geological evolution. We expect to observe a
wide variety of atmospheres and planets with alternative evolutionary paths,
with some planets resembling Earth at different epochs. For an Earth-like
atmospheric time trajectory, we simulate planets from prebiotic to current
atmosphere based on geological data. We use a stellar grid F0V to M8V
($T_\mathrm{eff}$ = 7000$\mskip3mu$K to 2400$\mskip3mu$K) to model four
geological epochs of Earth's history corresponding to a prebiotic world
(3.9$\mskip3mu$Ga), the rise of oxygen at 2.0$\mskip3mu$Ga and at
0.8$\mskip3mu$Ga, and the modern Earth. We show the VIS - IR spectral features,
with a focus on biosignatures through geological time for this grid of Sun-like
host stars and the effect of clouds on their spectra.
We find that the observability of biosignature gases reduces with increasing
cloud cover and increases with planetary age. The observability of the visible
O$_2$ feature for lower concentrations will partly depend on clouds, which
while slightly reducing the feature increase the overall reflectivity thus the
detectable flux of a planet. The depth of the IR ozone feature contributes
substantially to the opacity at lower oxygen concentrations especially for the
high near-UV stellar environments around F stars. Our results are a grid of
model spectra for atmospheres representative of Earth's geological history to
inform future observations and instrument design and are publicly available
online.