Natural gas, as we find it deep in the ground, was formed millions of years ago as countless ancient organisms broke down under great pressure and temperatures. This process released gases that were trapped in the layers of sediment, while the organic matter itself went on to become seams of coal or oil reservoirs, which is why gas reservoirs are often found nearby other fossil fuels.
Natural gas is mostly made of methane; around 20 per cent is other hydrocarbons plus impurities such as carbon dioxide and water. The entire gas processing system actually creates several commercial by-products in addition to the gas itself, including ethane, propane, butane and liquid condensate (in the case of condensate wells), which is sent for ‘cracking’ at an oil refinery.
The natural gas that enters your home is nearly pure methane and has no smell, which is why a chemical called mercaptan, or thiol, is added as a safety measure to create its distinctive odour.