In discussions about the smell surrounding landfills, the common theory is that it’s an overabundance of methane produced by rotting and fermenting material. Well, that is half true.
When organic matter decomposes, it gives off an odor that is most times considered to be offensive. Methane, however, is odorless. This makes it non-offensive to be around initially, but possibly dangerous if it unknowingly collects and ignites.