FIG. 3.
Reflectance spectrum of the Proterozoic Earth assuming 0.1% PAL O2 (Planavsky et al., 2014b), generated using the Atmos coupled climate-photochemical model (Arney et al., 2016). Note the absence of strong O2 features, but its photochemical byproduct O3 produces a relatively strong feature in the UV from 0.2 to 0.3 μm. This figure was generated using the LUVOIR simulator available at https://asd.gsfc.nasa.gov/luvoir and described in Robinson et al., (2016). LUVOIR, Large UltraViolet Optical Infrared Surveyor. (Credit: G. Arney)