Instruct: Given a question, retrieve relevant documents that answer the question.
Query: Where does methane come from naturally?
The Arctic region is one of the many natural sources of the greenhouse gas methane. Global warming accelerates its release, due to both release of methane from existing stores, and from methanogenesis in rotting biomass. Large quantities of methane are stored in the Arctic in natural gas deposits, permafrost, and as undersea clathrates. Permafrost and clathrates degrade on warming, thus large releases of methane from these sources may arise as a result of global warming. Other sources of methane include submarine taliks, river transport, ice complex retreat, submarine permafrost and decaying gas hydrate deposits.
Sewer gas can contain methane and hydrogen sulfide, both highly flammable and potentially explosive substances. As such, ignition of the gas is possible with flame or sparks.
The methane concentration in open sewers is lower (7 to 15 ppmv) than the closed drains (up to 300 ppmv) in samples collected 2 cm above the level of sewage.
The stability of the atmosphere in Earth is not a consequence of chemical equilibrium. Oxygen is a reactive compound, and should eventually combine with gases and minerals of the Earth's atmosphere and crust. Oxygen only began to persist in the atmosphere in small quantities about 50 million years before the start of the Great Oxygenation Event. Since the start of the Cambrian period, atmospheric oxygen concentrations have fluctuated between 15% and 35% of atmospheric volume. Traces of methane (at an amount of 100,000 tonnes produced per year) should not exist, as methane is combustible in an oxygen atmosphere.
The atmosphere contains various simple compounds such as water, methane (CH), hydrogen sulfide (HS), ammonia (NH) and phosphine (PH). Their abundances in the deep (below 10 bar) troposphere imply that the atmosphere of Jupiter is enriched in the elements carbon, nitrogen, sulfur and possibly oxygen by factor of 2–4 relative to the Sun. The noble gases argon, krypton and xenon also appear in abundance relative to solar levels (see table), while neon is scarcer. Other chemical compounds such as arsine (AsH) and germane (GeH) are present only in trace amounts. The upper atmosphere of Jupiter contains small amounts of simple hydrocarbons such as ethane, acetylene, and diacetylene, which form from methane under the influence of the solar ultraviolet radiation and charged particles coming from Jupiter's magnetosphere. The carbon dioxide, carbon monoxide and water present in the upper atmosphere are thought to originate from impacting comets, such as Shoemaker-Levy 9. The water cannot come from the troposphere because the cold tropopause acts like a cold trap, effectively preventing water from rising to the stratosphere (see Vertical structure above).
Fracking is a colloquial term for "horizontal drilling and hydraulic fracturing." During the 19th century natural gas was easy to extract from moderate depths using vertical wells. Sometimes wells were not needed at all because the gas was so plentiful it would bubble up from the ground. As non-renewable energy resources become more scarce, advances in fracking technology have allowed access to natural gas reserves accumulated in shale formations. Reserves of natural gas in the Marcellus Shale rock formation are valued at around $500 billion in Pennsylvania alone. 
While coal production in Appalachia has been in decline, advances in fracking technology have contributed to the regional "natural gas boom." The coal deposit of eastern Kentucky and southern West Virginia's coal fields have been mined longer than other reserves in the United States. The remaining deposits in these areas are deeper and the costs of extraction has increased.
Myanmar, is a developing country and an important natural gas and petroleum producer in Asia. It is home to one of the world's oldest petroleum industries, with its first crude oil exports dating back to 1853. Today, the country is one of the major natural gas producers in the Asian continent. Decades of isolation, sanctions, a lack of technical capacity, opaque government policies and insufficient investment has impeded the country's efforts to develop an upstream hydrocarbon sector. Recent but slow political reform has led the international community to ease sanctions on Burma, giving rise to hopes of greater investment and economic growth.
Tetrafluoromethane is the product when any carbon compound, including carbon itself, is burned in an atmosphere of fluorine. With hydrocarbons, hydrogen fluoride is a coproduct. It was first reported in 1926. It can also be prepared by the fluorination of carbon dioxide, carbon monoxide or phosgene with sulfur tetrafluoride. Commercially it is manufactured by the reaction of hydrogen fluoride with dichlorodifluoromethane or chlorotrifluoromethane; it is also produced during the electrolysis of metal fluorides MF, MF using a carbon electrode.
Polycyclic aromatic hydrocarbons (PAHs) are aromatic hydrocarbons that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH. PAHs occur in oil, coal, and tar deposits, and are produced as byproducts of fuel burning (whether fossil fuel or biomass). As pollutants, they are of concern because some compounds have been identified as carcinogenic, mutagenic, and teratogenic. PAHs are also found in cooked foods. Studies have shown that high levels of PAHs are found, for example, in meat cooked at high temperatures such as grilling or barbecuing, and in smoked fish.
Polycyclic aromatic hydrocarbons are discussed as possible starting materials for abiotic syntheses of materials required by the earliest forms of life.
The main concern raised against fracking is of the environment. In order to extract the gas, water and chemicals must be blasted into the shale at high pressures. This process concerns opponents of fracking because of the potentially chemical leaks into sub-surface aquifers, which could affect thousands of hectares of land for many years. Radioactive particles could also pollute groundwater, which is already scarce in the Karoo. Proponents of the process argue that a well-maintained regulatory environment, with emergency event control protocols, would prevent environmental catastrophes from occurring. In the United States, leakage has been reported in less than 1% of wells. Proponents also argue that more casing can be used while drilling to prevent leakages and environmentally friendly chemicals have been developed to prevent leaks from being harmful to local water supplies. Finally, proponents contend that aquifers depended on for human use in the Karoo are generally shallow, while shale pockets that could be extracted from are deeper, so contamination is less likely.
Jupiter's troposphere contains a complicated cloud structure. The upper clouds, located in the pressure range 0.6–0.9 bar, are made of ammonia ice. Below these ammonia ice clouds, denser clouds made of ammonium hydrosulfide ((NH)SH) or ammonium sulfide ((NH)S, between 1–2 bar) and water (3–7 bar) are thought to exist. There are no methane clouds as the temperatures are too high for it to condense. The water clouds form the densest layer of clouds and have the strongest influence on the dynamics of the atmosphere. This is a result of the higher condensation heat of water and higher water abundance as compared to the ammonia and hydrogen sulfide (oxygen is a more abundant chemical element than either nitrogen or sulfur). Various tropospheric (at 200–500 mbar) and stratospheric (at 10–100 mbar) haze layers reside above the main cloud layers. The latter are made from condensed heavy polycyclic aromatic hydrocarbons or hydrazine, which are generated in the upper stratosphere (1–100 μbar) from methane under the influence of the solar ultraviolet radiation (UV). The methane abundance relative to molecular hydrogen in the stratosphere is about 10, while the abundance ratio of other light hydrocarbons, like ethane and acetylene, to molecular hydrogen is about 10.
The Caspian Depression is below sea-level, consisting of large areas of marshlands in the eastern region. It is one of the largest flat lowland areas in Central Asia, covering approximately . The area is very rich in underground oil and gas reserves, and oil and natural gas pipelines cross the depression from north to south and east to west. Many geologists believe the Caspian Sea and the depression were formed by tectonic forces. Some of them also believe that the North Caspian depression became separated from the open ocean in ancient times to form an enormous salt lake. Part of the ancient Silk Road ran through this region. The two largest cities in the depression are Astrakhan in Russia, and Atyrau in Kazakhstan. Today, the region is used mainly for livestock raising.
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually not found in organisms, but instead as three main classes of esters: triglycerides, phospholipids, and cholesterol esters. In any of these forms, fatty acids are both important dietary sources of fuel for animals and they are important structural components for cells.
The conversion of nitrogen gas (N) into nitrates and nitrites through atmospheric, industrial and biological processes is called nitrogen fixation. 
Atmospheric nitrogen must be processed, or "fixed", into a usable form to be taken up by plants. Between 5x10 and 10x10 g per year are fixed by lightning strikes, but most fixation is done by free-living or symbiotic bacteria known as diazotrophs. These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia, which is converted by the bacteria into other organic compounds. Most biological nitrogen fixation occurs by the activity of Mo-nitrogenase, found in a wide variety of bacteria and some Archaea. Mo-nitrogenase is a complex two-component enzyme that has multiple metal-containing prosthetic groups. An example of free-living bacteria is "Azotobacter". Symbiotic nitrogen-fixing bacteria such as "Rhizobium" usually live in the root nodules of legumes (such as peas, alfalfa, and locust trees). Here they form a mutualistic relationship with the plant, producing ammonia in exchange for carbohydrates. Because of this relationship, legumes will often increase the nitrogen content of nitrogen-poor soils. A few non-legumes can also form such symbioses. Today, about 30% of the total fixed nitrogen is produced industrially using the Haber-Bosch process, which uses high temperatures and pressures to convert nitrogen gas and a hydrogen source (natural gas or petroleum) into ammonia.
The growing awareness of the negative effects of embalming fluid on the environment has caused some people to consider green burials where there are either no harsh chemicals used in the embalming process. As a result embalming chemical manufacturers now offer less effective "Green" Chemicals, as an option. For example the Champion Company began producing their Enigma Line in the early 2000's and these fluids are approved by the Green Burial Council or there is no embalming process at all.
People of lower socioeconomic status are found to be more vulnerable to air pollutant, PM 2.5, due to their location. PM 2.5 is an air pollutant, arising from the blend of power plants, refineries, and diesel engines, among other sources, and this particle penetrates the lungs. Communities of low socioeconomic statuses are frequently concentrated in areas near highways, busy roads, and refineries. Therefore, limiting one's exposure to air pollution in an impoverished environment is nearly impossible. Communities of low socioeconomic status face an unequal access to environmental health services and resources.
Originally a land-locked fresh water lake, the Black Sea was flooded with salt water from the Mediterranean Sea during the Holocene. The influx of salt water essentially smothered the fresh water below it because a lack of internal motion and mixing meant that no fresh oxygen reached the deep waters, creating a meromictic body of water. The anoxic environment, which is hostile to many biological organisms that destroy wood in the oxygenated waters, provides an excellent testing site for deep water archaeological survey.
In addition to protecting against mining contamination, Idaho Conservation League works to protect Idaho’s ground water from hydraulic fracturing, otherwise known as “fracking,” a process used in natural gas extraction. When a natural gas company began exploration in western Idaho in 2011, ICL asked the Idaho oil and Gas Conservation Commission to prohibit carcinogenic chemicals and require companies to provide a bond protecting Idaho communities in the case of a fracking emergency. ICL has one main goal in regards to fracking, that "Idaho has rules protective of the people's groundwater" that set limitations on the use of hazardous substances.
A very wide variety of fuels may occur as gases, droplet fogs, or dust suspensions. Oxidants include halogens, ozone, hydrogen peroxide and oxides of nitrogen. Gaseous detonations are often associated with a mixture of fuel and oxidant in a composition somewhat below conventional flammability ratios. They happen most often in confined systems, but they sometimes occur in large vapor clouds. Other materials, such as acetylene, ozone, and hydrogen peroxide are detonable in the absence of dioxygen.
Platinum is a member of the platinum group of elements and group 10 of the periodic table of elements. It has six naturally occurring isotopes. It is one of the rarer elements in Earth's crust, with an average abundance of approximately 5 μg/kg. It occurs in some nickel and copper ores along with some native deposits, mostly in South Africa, which accounts for 80% of the world production. Because of its scarcity in Earth's crust, only a few hundred tonnes are produced annually, and given its important uses, it is highly valuable and is a major precious metal commodity.
According to the National Resources Defense Council, cancer causing pollutants such as benzene, formaldehyde, and diesel have been found in the air near fracking sites. These pollutants generate wastewater, which is linked to groundwater contamination, threatening nearby drinking water and causing concern for anyone who is exposed. Studies done by The National Institute for Occupational Safety and Health, found that “Fracking also uses crystalline silica, which is a type of sand that’s used to keep the fractures open.” Exposure to this, along with dust and other air pollutants produced from fracking, can cause respiratory problems.
Today most methanol is produced from methane through syngas. Trinidad and Tobago is currently the world's largest methanol exporter, with exports mainly to the United States. The natural gas that serves as feedstock for the production of methanol comes from the same sources as other uses. Unconventional gas resources such as coalbed methane, tight sand gas and eventually the very large methane hydrate resources present under the continental shelves of the seas and Siberian and Canadian tundra could also be used to provide the necessary gas.
Another source of methane emissions has been identified in Russia. Near Yamburg and Urengoy exist gas fields with a methane concentration of 97 percent. The gas obtained from these fields is taken and exported to Western and Central Europe through an extensive pipeline system known as the Trans-Siberian natural gas pipeline system. In accordance with the IPCC and other natural gas emissions control groups, measurements had to be taken throughout the pipeline to measure methane emissions from technological discharges and leaks at the pipeline fittings and vents. Although the majority of the natural gas leaks were carbon dioxide, a significant amount of methane was also being consistently released from the pipeline as a result of leaks and breakdowns. In 2001, natural gas emissions from the pipeline and natural gas transportation system accounted for 1 percent of the natural gas produced. Fortunately, between 2001 and 2005, this number reduced to 0.7 percent, and even the 2001 value is still significantly less than that of 1996.
Tens of thousands of methane wells have been drilled, and extensive support facilities such as roads, pipelines, and compressors have been installed for CBM extraction in the Powder River Basin of northeast Wyoming and southeast Montana and now in India at West Bengal- Ranigunj, Panagarh etc. Seven percent of the natural gas (methane) currently produced in the United States comes from CBM extraction. Methane from coalbed reservoirs can be recovered economically, but disposal of water is an environmental concern.
According to officials at the L.A. Department of Building and Safety, "Methane is an old story in Los Angeles and the standards the city requires at Playa Vista are the strictest in the country. Hence, Playa residents we spoke to cited areas where the gas has not been mitigated - such as Venice, Santa Monica, and nearly all of the Westside - as more dangerous." Many also argue that "much of the methane is natural - not the kind that comes from the gas company."