Where does most methane come from? Some can be traced to non-biological sources, including volcanic eruptions and serpentinization reactions on the ocean floor. 90-95% of the methane on Earth, however has a biological origin.

The two main types of biological methane are thermogenic and biogenic. Thermogenic methane is produced deep in the ground from the buried remains of organisms, which gradually become fossil fuels after being exposed to heat and pressure for centuries. Biogenic methane (biogas) is produced by methanogens, methane-producing micro-organisms that are usually found in anaerobic environments.

How will your lab test these isotopic ratios?
In your lab, you use the stable isotope ratios of carbon (¹³C/¹²C) and deuterium/hydrogen (²H/¹H or D/H) to determine the origin of methane samples. to do this, you combust a pure methane sample, producing carbon dioxide and water. The CO₂ is purified and then tested with a Mass Spectrometer. You can calculate the ¹³C/¹²C ratio by dividing the intensity of peak 45(¹³C¹⁶₂) by that of the peak 44(¹²C¹⁶₂). For added certainty, you sometimes also find deuterium/hydrogen ratios from the water that was produced in combustion.