Question

In 2004, atmospheric methane ($CH_4$) was detected on Mars. Because methane is rapidly destroyed by solar ultraviolet radiation in the Martian atmosphere, its ongoing presence implies an active source. Two scientists discuss whether this methane has a biological or non-biological origin.

Scientist 1
The atmospheric methane on Mars is produced by subterranean methanogenic microbes. These microbes reside deep underground where liquid water is present and geothermal heat provides a stable environment. They metabolize carbon dioxide ($CO_2$) and hydrogen ($H_2$) to produce methane. The seasonal fluctuations in atmospheric methane levels observed by orbiters are due to changes in microbial metabolic activity; as subterranean temperatures rise during the Martian summer, the microbes become more active and produce more methane, which then diffuses to the surface.

Scientist 2
The atmospheric methane on Mars is abiotic, produced by serpentinization—a chemical reaction between water, dissolved carbon dioxide, and olivine-rich rocks in the Martian crust. This reaction occurs deep underground at high temperatures. The methane is stored in subsurface ice cages called clathrates. The seasonal fluctuations in atmospheric methane levels are not caused by changes in the rate of methane production, but rather by the seasonal melting of surface ice seals. During the Martian summer, increased solar radiation warms the surface, cracking the ice seals and allowing trapped methane to escape into the atmosphere.

Scientist 1 and Scientist 2 differ in their views regarding which of the following aspects of Martian methane?