The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. This transformation can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is nitrogen, making it the largest pool of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems. The nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes, including primary production and decomposition. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle]citation needed[.
A 2011 study found that nitrogen from rocks may also be a significant source of nitrogen, that had not previously been included in most calculations and statistics.
Daidokoro (台所;lit. "kitchen") is the place where food is prepared in a Japanese house. Until the Meiji era, a kitchen was also called kamado (かまど; lit. stove) and there are many sayings in the Japanese language that involve kamado as it was considered the symbol of a house. The term could even be used to mean "family" or "household" (much as "hearth" does in English). Separating a family was called kamado wo wakeru, or "divide the stove". kamado wo yaburu (lit. "break the stove") means that the family was broken.
In the Jōmon period, from the 10,000 BC to 300 BC, people gathered into villages, where they lived in shallow pit dwellings. These simple huts were between 10 to 30 square meters and had a hearth in the center. Early stoves were nothing more than a shallow pit (jikaro 地床炉), but they were soon surrounded by stones to catch the fire sparks. A bottomless clay vase soon replaced the stones as these became hot quickly and occupants had to be careful around a stove. This type of stove is called umigamero (埋甕炉; lit. "buried vase stove"). As the stove became safer, it was moved from the center of house to the side and, by the late Kofun period (6th century), almost all houses had a stove at one end of the house. Some rich families in the Kofun period built a separate house where cooking was done. In these houses, food was stored in sacks and pots in a hole dug on the floor. Houses were constructed near a river or a spring for easy access to water.
Household chemicals are non-food chemicals that are commonly found and used in and around the average household. They are a type of consumer goods, designed particularly to assist cleaning, pest control and general hygiene purposes.
Food additives generally do not fall under this category, unless they have a use other than for human consumption. Cosmetics products can partially be counted in, because even though they are not for direct application to parts of the human body, they may contain artificial additives that have nothing to do with their dedicated purpose (e.g. preservatives and fragrances in hair spray). Additives in general (e.g. stabilizers and coloring found in washing powder and dishwasher detergents) make the classification of household chemicals more complex, especially in terms of health - some of these chemicals are irritants or potent allergens - and ecological effects.