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Archean Haze Models

During the Archean Eon (approximately $4.0$ to $2.5$ billion years ago), Earth's atmosphere was rich in methane ($CH_4$) and carbon dioxide ($CO_2$) but lacked oxygen ($O_2$). Solar ultraviolet (UV) radiation drove photochemical reactions in this atmosphere, producing a hydrocarbon haze. Proponents of three models debate the characteristics and climate impacts of this Archean haze.

Model 1 (Organic Haze Model)
Proponents of Model 1 propose that the haze was composed of complex organic polymers formed at high altitudes (above $40\text{ km}$) where solar UV flux was greatest. These polymer particles grew as fluffy, fractal aggregates (non-spherical shapes). Proponents believe that because of their high fractal dimension, the aggregates scattered incoming solar radiation poorly but allowed thermal infrared radiation from Earth's surface to pass through. Thus, the haze did not cause global cooling (an "anti-greenhouse" effect), allowing $CH_4$ and $CO_2$ in the lower atmosphere to maintain liquid surface water.

Model 2 (Sulfate-Shielded Haze Model)
Proponents of Model 2 argue that volcanic emissions of sulfur dioxide ($SO_2$) reacted with atmospheric water vapor, forming sulfate ($H_2SO_4$) aerosols in the lower atmosphere (below $15\text{ km}$). These polar sulfate droplets coated the organic polymers, causing the aggregate structures to collapse into compact, smooth spheres. Proponents believe that these spherical particles highly efficiently scattered incoming solar radiation back into space, creating a strong anti-greenhouse cooling effect. Proponents assume that surface liquid water was maintained only because the cooling was offset by extremely high concentrations of greenhouse gases ($CO_2$ and $H_2S$) trapped in the lower troposphere.

Model 3 (Biogenic Carbonate Haze Model)
Proponents of Model 3 suggest that windblown biogenic carbonate dust ($CaCO_3$) from early microbial mats served as the primary nucleation sites for organic haze throughout the entire atmospheric column. These composite dust-organic particles had a carbonate core and an organic shell. Proponents believe that this unique structure allowed the haze to actively absorb outgoing thermal infrared radiation, directly contributing to greenhouse warming. Proponents assume that a biological feedback loop existed: cooler surface temperatures reduced microbial activity, decreasing carbonate dust emission and haze density, which subsequently mitigated cooling.

Based on the descriptions of Model 2 and Model 3, the proponents of these two models would most likely disagree on which of the following questions regarding the Archean atmospheric haze?