The carbon cycle and the oxygen cycle (environmental science)

Part 4 of the carbon cycle

CO2 flux also occurs between the atmosphere and oceans. CO2 is more soluble in cool water than warm water. This is why it tends to be transferred from the warmer parts of the ocean to the atmosphere (90 Pg/year). Similarly, CO2 is transferred from the atmosphere to the cooler parts of the ocean (92 Pg/year). The activity of burning fossil fuel contributes greatly to the flux of CO2 in the atmosphere (6 Pg/year). This carbon was initially a part of the lithosphere in the form of coal and petroleum. The process of burning of fossil fuel largely has altered the carbon cycle relative to its natural state, thereby increasing the CO2 concentration in the atmosphere.

The Carbon Cycle

Carbon, in its organic and inorganic forms, is stored in the Earth in a number of categories or pools. The four most prominent pools include the Earth's crust, oceans, atmosphere, and the biosphere. About 99.9 percent of the carbon on Earth is stored in sedimentary rocks. It amounts to about 100,000,000 petagrams of carbon (PgC, where one petagram is one billion tons). The carbon is largely stored in carbonate mineral form; however, it is also present as organic matter. The Earth's crust also stores 4,000 PgC as petroleum hydrocarbons. The ocean is the second largest pool of carbon deposits. It consists of about 38,000 PgC of dissolved inorganic carbon. The atmosphere contains merely 750 PgC of carbon in the form of CO2. The biosphere contains 560 PgC. The soil contains an additional 1,500 PgC, mainly in the form of organic carbon.

Part 2 of Importance of Carbon and Oxygen to Life

In its inorganic form, carbon is usually found in solid forms. Examples include diamond, graphite, and carbonates. Carbon bonds with oxygen to form carbon dioxide (CO2). Carbonates are derived from carbon dioxide, its dissolved forms (carbonate), and the mineral precipitates of its dissolved forms (calcium carbonate). For example, the shells of oysters and snails are composed of calcium carbonate. Terrestrial plants acquire carbon present in the atmosphere. Aquatic plants obtain their carbon requirements from the carbonates that are dissolved in water. Autotrophs are organisms that convert inorganic substances to nutritional organic substances through light or chemical energy (photosynthesis) for their subsistence. They produce organic compounds and oxygen from water and carbon dioxide. Algae and certain types of bacteria are examples of autotrophs.

Importance of Carbon and Oxygen to Life

Living organisms need both carbon and oxygen to survive, grow, and reproduce. Carbon is a resource that is finite in nature; however, it cycles through the Earth in several forms. This process ensures that carbon is available in most places wherever it is required, namely for living organisms, the atmosphere, and water bodies. Environmental chemists describe carbon as existing in organic and inorganic forms. In its organic form, carbon is usually (not always) related to the metabolic processes of living organisms. It is found in compounds such as amino acids, alcohols, oils, hydrocarbon gases, and carbohydrates, among others. The organic carbon molecules are complex in nature. Most of the compounds present in the cells of living organisms are considered to be organic. This way, it is quite evident that carbon indeed is essential to life.

Part 2 of the carbon cycle

Movement of material from one particular place to another is known as flux. It is also defined as the rate of transfer from one reservoir to another. Carbon fluxes indicate the movement of carbon from one pool to another. Several processes result in the flux of carbon between the surface of the Earth and its lithosphere (crust of the Earth). Volcanic activity is responsible for about 0.1 Pg/year flux of carbon from the lithosphere to the atmosphere and oceans. Organic and inorganic carbon flux (0.1 Pg/year) occurs due to sedimentation in the lakes and oceans. The chemical process of weathering of rocks is responsible for releasing the carbon stored in it. The chemical process also converts CO2 from the atmosphere to dissolved carbonates. The carbon is released as dissolved inorganic carbon in rivers, which is then transferred to the oceans (0.8 Pg/year).

Part 3 of Importance of Carbon and Oxygen to Life

Oxygen is essential to life because most organisms consume oxygen and produce carbon dioxide. Oxygen forms about one fifth of the atmosphere. However, in its organic molecular form, it is found in smaller proportion than carbon. Carbonate compounds such as CO2 have a higher percentage of oxygen in their composition. The process of photosynthesis by autotrophs cannot be completed without this gas. Oxygen easily combines with most elements to form compounds. Water (H2O) is the most common compound of oxygen. Ozone (O3) is a type of oxygen that is pale blue in color. It is poisonous and explosive by nature. O3 forms a part of the upper atmosphere known as the ozone layer. It is helpful in that state because it protects the Earth's surface from the sun's ultraviolet radiation. CO2, being an important greenhouse gas, helps in regulating the Earth's climate.

The Oxygen Cycle

Oxygen is one of the most important elements on Earth because most organisms need it to create energy in living cells, by the process of respiration. Oxygen also forms the largest components of most rock-forming minerals, containing about 46.6 percent of the Earth's crust and 94 percent of its volume. The ice and water present on the Earth form the next large reservoir of oxygen. The water molecules contain 89 percent oxygen by mass. Thus, almost all the Earth's water is formed from oxygen. Similarly, the human body, being mostly comprised of water, has a mass that contains about 65 percent of oxygen.

Part 3 of the oxygen cycle

The O2 gets absorbed at the surface level of the water bodies. It sometimes gets exhausted in sediments and deep lakes because of the process of organic matter decomposition. This results in anoxic conditions. Anoxic waters are those portions of water bodies that have a depleted oxygen content. The ozone layer helps protect the Earth's surface from the ultraviolet (UV) rays of the sun. The UV rays react with the O2 molecules, thereby leading to the depletion of the ozone layer. The oxygen cycle is linked to the carbon cycle because oxygen and carbon are usually combined in a molecule.

Part 2 of the oxygen cycle

The molecular oxygen (O2) comprises about 21 percent of the atmosphere, Earth1.1×1018 kg by weight. To a certain extent, the oxygen and carbon cycle overlap. This is because oxygen combines with carbon to form carbon dioxide. Thus, the carbon cycle that involves carbon dioxide forms a part of the oxygen cycle as well. Dissolved O2 is found in the Earth's water bodies. Just like CO2, O2 is less soluble in warm water than in cool water. Thus, the cooler parts of the oceans have a higher quantity of dissolved O2 when compared to the warmer parts of the water bodies. Just like the living beings on land, even the aquatic animals consume O2 and produce CO2. The autotrophs consume CO2 and produce O2 during the process of photosynthesis.

Part 3 of the carbon cycle

The process of photosynthesis converts inorganic carbon to organic carbon in the biosphere (120 Pg/year). Again, a high proportion of the organic carbon is utilized as energy by plants that release it back to the atmosphere in the form of CO2 (60 Pg/year). Soils also contain organic matter in the form of litterfall (transfer of dead organic matter such as stems and leaves from the trees and plants to the ground). The decomposers such as bacteria, fungi, worms, and so on in the soil further convert the organic matter back to CO2 by decomposing it (60 Pg/year). Usage of land and deforestation also contribute toward the same (0.9 Pg/year).

What is an example of inorganic form of carbon? - shells of oyster - graphite - water - aerobic respiration

graphite

Which natural activity consists of transferring dead organic material to the ground? - volcanic activity - burning of fossil fuel - litterfall - photosynthesis

litterfall

Where can you find dissolved O2? - rocks - air - ozone layer - oceans

oceans