In general, irregular periods are very common during the perimenopause. The most common early menstrual irregularity noticed in the perimenopause is a shortening of cycle length.
Abiogenic petroleum origin. Abiogenic petroleum origin is a term used to describe a number of different hypotheses which propose that petroleum and natural gas are formed by inorganic means rather than by the decomposition of organisms.
Gas inside the coal. Hydrocarbon gases are formed in coal beds during the coal matter metamorphism process, i.e. changing of its structure, properties, and composition under exposure to temperature and pressure. Their main component is methane, whose concentration in the mixture reaches from 80 to 98 per cent.