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.
Back to the Energy Systems Map. Conventional Gas refers to natural gas that can be produced from reservoirs using traditional drilling, pumping and compression techniques. Natural gas is a hydrocarbon gas formed over thousands of years from the burying of dead plants and animals.