Question

Although the Martian atmosphere is composed primarily of carbon dioxide ($CO_2$), planetary missions have detected trace amounts of methane ($CH_4$). Because atmospheric methane is rapidly destroyed by solar ultraviolet radiation, its persistent presence suggests an ongoing source of replenishment. Scientists have proposed two models to explain the origin and release of methane on Mars.

Model 1 (Biogenic Hypothesis)
Martian methane is produced by subsurface methanogenic archaea residing in deep liquid-water aquifers. These micro-organisms consume carbon dioxide and hydrogen gas ($H_2$) to sustain their metabolism, releasing methane as a byproduct. Proponents of Model 1 believe that subsurface biological activity is directly influenced by seasonal temperature cycles. During the Martian summer, localized subsurface warming increases microbial metabolic rates and causes thermal expansion of the aquifers, forcing accumulated methane gas upward through seasonal fractures in the overlying cryosphere.

Model 2 (Abiogenic Hypothesis)
Martian methane is produced abiotically through serpentinization, a reaction between water and ultramafic rocks rich in the mineral olivine ($(Mg,Fe)_2SiO_4$) within the Martian crust. This reaction occurs at high temperatures and pressures deep underground, yielding hydrogen gas ($H_2$) as a byproduct. The hydrogen subsequently reacts with dissolved carbon dioxide ($CO_2$) via a mineral-catalyzed Fischer-Tropsch-type synthesis to form methane. Proponents of Model 2 believe that because geothermal heat is stable, methane production occurs at a constant rate. Its release into the atmosphere is regulated solely by episodic tectonic fracturing that opens pathways from the deep crust to the surface, completely independent of seasonal variations in surface temperature.

Which of the following assumptions is implicitly required by Model 1's hypothesis regarding the seasonal variation of Martian atmospheric methane, but is NOT required by Model 2?