Question

Methane ($CH_4$) has been detected in trace amounts in the Martian atmosphere. The passage below presents two models explaining its origin.

### Models of Martian Methane
Methane ($CH_4$) has been detected in trace amounts in the Martian atmosphere. Because atmospheric methane is rapidly destroyed by ultraviolet (UV) photolysis, with a chemical lifetime of approximately $300$ years, its ongoing presence implies a modern source of replenishment. Scientists have proposed two primary models to explain the source of Martian methane.

Model 1 (Biotic Origin)
Model 1 proposes that Martian methane is produced by subsurface microbial life (methanogens). These micro-organisms live deep underground where liquid water is available, utilizing carbon dioxide ($CO_2$) and hydrogen ($H_2$) to produce energy, releasing methane as a metabolic byproduct. Methane release under this model is seasonally dynamic, peaking during warmer seasons when microbial activity increases and subsurface transport pathways open. The model predicts that Martian methane will show a high depletion of carbon-13 ($^{13}\text{C}$), a signature characteristic of biological carbon fixation.

Model 2 (Abiotic Origin)
Model 2 proposes that Martian methane is produced by serpentinization, an abiotic geological process. In this process, liquid water circulating deep within the crust reacts with magnesium- and iron-rich silicate minerals (such as olivine, $(\text{Mg},\text{Fe})_2\text{SiO}_4$). This reaction releases hydrogen gas ($H_2$), which subsequently reacts with dissolved carbon dioxide via Fischer-Tropsch-type reactions to form methane. Under this model, methane is trapped in underground clathrate hydrates and released episodically into the atmosphere through tectonic fractures. The isotopic signature of this methane is expected to show standard geological $^{13}\text{C}$ levels, with significantly less carbon-13 depletion than biologically produced methane.

Based on the models provided, match each statement regarding Martian methane to the model(s) that support it.