How are biogenic methane and thermal methane formed differently?

Biogenic methane and thermal methane are formed through distinct geological and biological processes:

• Biogenic Methane: This gas is produced during the immature, or biological, stage of petroleum formation. It results from the decomposition of organic material by anaerobic microorganisms (methanogenic archaea) that cannot tolerate oxygen or high concentrations of sulfate. Because of these requirements, biogenic gas generation is restricted to specific environments, such as swamps, marshes, and certain marine environments beneath the zone of active sulfate reduction.12

• Thermal Methane: This gas is generated during the postmature stage, typically at depths below 5,000 metres (16,000 feet), where temperatures are high enough that liquid hydrocarbons are no longer stable. Thermal methane is the product of the "cracking" or thermal destruction of existing liquid hydrocarbons. Unlike biogenic methane, which relies on microbial activity, thermal methane is a result of geological heat and pressure acting on organic matter over long periods.31