<P> Biogas typically refers to a mixture of gases produced by the breakdown of organic matter in the absence of oxygen . Biogas is produced by anaerobic digestion with anaerobic bacteria or fermentation of biodegradable materials such as manure, sewage, municipal waste, green waste, plant material, and crops . It is primarily methane (CH) and carbon dioxide (CO) and may have small amounts of hydrogen sulphide (H S), moisture and siloxanes . </P> <P> Natural fibres are a class of hair - like materials that are continuous filaments or are in discrete elongated pieces, similar to pieces of thread . They can be used as a component of composite materials . They can also be matted into sheets to make products such as paper or felt . Fibres are of two types: natural fibre which consists of animal and plant fibres, and man made fibre which consists of synthetic fibres and regenerated fibres . </P> <P> Renewable resources are endangered by non-regulated industrial developments and growth . They must be carefully managed to avoid exceeding the natural world's capacity to replenish them . A life cycle assessment provides a systematic means of evaluating renewability . This is a matter of sustainability in the natural environment . </P> <P> National Geographic has described ocean over fishing as "simply the taking of wildlife from the sea at rates too high for fished species to replace themselves ." </P>

Land is a renewable resource because it can be formed by natural processes