I’m one of those who think Natural Gas was here from the beginning of the planet..................
Some probably was. Methane is the most stable form (without the presences of oxygen) for Carbon and Hydrogen to exist. But decaying matter clearly produces methane. Swamps, dumps, etc, all produce methane. When algae, plankton, etc, gets trapped in sediment on the bottoms of oceans and lakes, then gets covered up under layer and layer, having methane down there should be expected.