CHAPTER TWO Alkanes METHANE AND THE BIOSPHERE* ne of the things that environmental scientists the atmosphere, but most of the rest simply ends up do is to keep track of important elements in completing the carbon cycle. It exits the anaerobic the biosphere-in what form do these ele- environment where it was formed and enters the ments normally occur, to what are they transformed, aerobic world where it is eventually converted to car and how are they returned to their normal state? bon dioxide by a variety of processes Careful studies have given clear, although compli- When we consider of methane we have cated, pictures of the"nitrogen cycle, the"sulfur cy- to add" old"methane, methane that was formed carbon ge.cycle, "begins ano ycle, " for example. The millions of years ago but became trapped beneath cle, "and the"phosphorus ends with atmospheric the earth's surface, to the"new"methane just d oxide. It can be represented in an abbrevi- scribed Firedamp, an explosion hazard to miners, oc- in layers of coal and is mostly methane. Petro- leum deposits, formed by microbial decomposition of CO2+ H2o+ energy carbohydrates plant material under anaerobic conditions, are al ways accompanied by pockets of natural gas, which is respiration An interesting thing happens when trapped ubstances of methane leaks from sites under the deep ocean floor. If the pres eno h (50 atm) and th cold enough(4oC), the methane doesn't simply bub Methane is one of literally millions of com- ble to the surface. Individual methane molecules be pounds in the carbon cycle, but one of the most come trapped inside clusters of 6-18 water molecules abundant. It is formed when carbon-containing com- forming methane clathrates or methane hydrates pounds decompose in the absence of air (anaerobic Aggregates of these clathrates stay at the bottom of conditions). The organisms that bring this about are the ocean in what looks like a lump of dirty ice.Ice called methanoarchaea. Cells can be divided into that burns. Far from being mere curiosities, methane three types: archaea, bacteria, and eukarya. clathrates are potential sources of energy on a scale Methanoarchaea are one kind of archaea and may greater than that of all known oil reserves combined rank among the oldest living things on earth. They At present, it is not economically practical to extract can convert a number of carbon-containing com- the methane however pounds, including carbon dioxide and acetic acid, to Methane clathrates have received recent atten- methane tion from a different segment of the scientific com- Virtually anywhere water contacts organic mat- munity. While diving in the Gulf of Mexico in 1997, a ter in the absence of air is a suitable place for research team of biologists and environmental scien- methanoarchaea to thrive--at the bottom of ponds, tists were surprised to find a new species of worm bogs, and rice fields, for example. Marsh gas (swamp grazing on the mound of a methane clathrate.What gas) is mostly methane Methanoarchaea live inside were these worms feeding on? Methane? Bacteria termites and grass-eating animals. One source quotes that live on the methane? A host of questions having 20 L/day as the methane output of a large cow. to do with deep-ocean ecosystems suddenly The scale on which methanoarchaea churn out emerged. Stay tuned methane, estimated to be 10 1-10'2 lb/year, is enor "The biosphere is the part of the earth where life is; it includes the mous. About 10% of this amount makes its way into surface, the oceans, and the lower atmospher n-Butane and isobutane have the same molecular formula but differ in the order in which their atoms are connected. They are constitutional isomers of each other (Section 1.8). Because they are different in structure, they can have different properties. Both are gases at room temperature, but n-butane boils almost 10C higher than isobutane and has a melting point that is over 20C higher Back Forward Main MenuToc Study Guide ToC Student o MHHE Website58 CHAPTER TWO Alkanes METHANE AND THE BIOSPHERE* One of the things that environmental scientists do is to keep track of important elements in the biosphere—in what form do these ele￾ments normally occur, to what are they transformed, and how are they returned to their normal state? Careful studies have given clear, although compli￾cated, pictures of the “nitrogen cycle,” the “sulfur cy￾cle,” and the “phosphorus cycle,” for example. The “carbon cycle,” begins and ends with atmospheric carbon dioxide. It can be represented in an abbrevi￾ated form as: Methane is one of literally millions of com￾pounds in the carbon cycle, but one of the most abundant. It is formed when carbon-containing com￾pounds decompose in the absence of air (anaerobic conditions). The organisms that bring this about are called methanoarchaea. Cells can be divided into three types: archaea, bacteria, and eukarya. Methanoarchaea are one kind of archaea and may rank among the oldest living things on earth. They can convert a number of carbon-containing com￾pounds, including carbon dioxide and acetic acid, to methane. Virtually anywhere water contacts organic mat￾ter in the absence of air is a suitable place for methanoarchaea to thrive—at the bottom of ponds, bogs, and rice fields, for example. Marsh gas (swamp gas) is mostly methane. Methanoarchaea live inside termites and grass-eating animals. One source quotes 20 L/day as the methane output of a large cow. The scale on which methanoarchaea churn out methane, estimated to be 1011–1012 lb/year, is enor￾mous. About 10% of this amount makes its way into CO2 H2O energy carbohydrates naturally occurring substances of numerous types photosynthesis respiration respiration the atmosphere, but most of the rest simply ends up completing the carbon cycle. It exits the anaerobic environment where it was formed and enters the aerobic world where it is eventually converted to car￾bon dioxide by a variety of processes. When we consider sources of methane we have to add “old” methane, methane that was formed millions of years ago but became trapped beneath the earth’s surface, to the “new” methane just de￾scribed. Firedamp, an explosion hazard to miners, oc￾curs in layers of coal and is mostly methane. Petro￾leum deposits, formed by microbial decomposition of plant material under anaerobic conditions, are al￾ways accompanied by pockets of natural gas, which is mostly methane. An interesting thing happens when trapped methane leaks from sites under the deep ocean floor. If the pressure is high enough (50 atm) and the water cold enough (4°C), the methane doesn’t simply bub￾ble to the surface. Individual methane molecules be￾come trapped inside clusters of 6–18 water molecules forming methane clathrates or methane hydrates. Aggregates of these clathrates stay at the bottom of the ocean in what looks like a lump of dirty ice. Ice that burns. Far from being mere curiosities, methane clathrates are potential sources of energy on a scale greater than that of all known oil reserves combined. At present, it is not economically practical to extract the methane, however. Methane clathrates have received recent atten￾tion from a different segment of the scientific com￾munity. While diving in the Gulf of Mexico in 1997, a research team of biologists and environmental scien￾tists were surprised to find a new species of worm grazing on the mound of a methane clathrate. What were these worms feeding on? Methane? Bacteria that live on the methane? A host of questions having to do with deep-ocean ecosystems suddenly emerged. Stay tuned. *The biosphere is the part of the earth where life is; it includes the surface, the oceans, and the lower atmosphere. n-Butane and isobutane have the same molecular formula but differ in the order in which their atoms are connected. They are constitutional isomers of each other (Section 1.8). Because they are different in structure, they can have different properties. Both are gases at room temperature, but n-butane boils almost 10°C higher than isobutane and has a melting point that is over 20°C higher. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website