Without air; the opposite of aerobic. This term is used to describe environmental conditions where oxygen is not present and where decay of organic material is partially or completely stopped. Anaerobic conditions are usually waterlogged but may also occur when a layer or clay, plant, or animal remains is sealed. The remains survive much better than under normal conditions because there is insufficient oxygen for bacterial or fungal growth. The organic materials reach a state of equilibrium beyond which they do not decay.