How the Earth Recycles Elements: Biogeochemical Cycles

The way in which an element—or, in some cases, a compound such as water—moves between living factors also called biotic factors  and nonliving factors also called abiotic factors is called a biogeochemical cycle. This name reflects the importance of chemistry and geology as well as biology in helping us understand these cycles.

Which biogeochemical cycles are key to life? 

Water, Carbon, Hydrogen, Nitrogen,  Oxygen,  Phosphorus, and Sulfur are conserved in biogeochemical cycles.

The water cycle, also known as the hydrologic cycle, is the continuous movement of water on, above, and below the surface of the Earth. It is a complex system that involves water exchange between the atmosphere, land, and oceans. The water cycle is essential for life on Earth, as it provides us with the freshwater we need to survive.

hydrogen cycle

The carbon cycle begins with photosynthesis. During photosynthesis, plants use carbon dioxide from the atmosphere to create glucose, which is a sugar that plants use for energy. When plants die, their remains are broken down by decomposers, such as bacteria and fungi. This process releases carbon dioxide back into the atmosphere.

Carbon can also be released into the atmosphere through other processes, such as respiration, combustion, and volcanic eruptions. Respiration is the process by which living things use oxygen to break down glucose for energy. Combustion is the process of burning, which releases carbon dioxide into the atmosphere. Volcanic eruptions can also release carbon dioxide into the atmosphere.


The hydrogen cycle is the process by which hydrogen atoms continually travel from the Earth’s surface to the atmosphere and back to the Earth’s surface. This biogeochemical process  involves both living (biotic) and nonliving (abiotic) factors.


oxygen cycle

The oxygen cycle begins with the production of oxygen by plants through photosynthesis. Plants use sunlight, water, and carbon dioxide to produce glucose and oxygen. The oxygen that is produced by plants is released into the atmosphere, where it is used by animals and other organisms for respiration.

Respiration is the process by which organisms break down food to produce energy. During respiration, oxygen is consumed and carbon dioxide is produced. The carbon dioxide that is produced by organisms is released into the atmosphere, where it is used by plants for photosynthesis.

The oxygen cycle also involves the exchange of oxygen between the atmosphere and the oceans. Oxygen is dissolved in ocean water and is used by marine organisms for respiration. The oxygen that is dissolved in ocean water is also exchanged with the atmosphere through the process of diffusion.

The oxygen cycle is an important part of the Earth’s climate system. Oxygen is a greenhouse gas, and it helps to regulate the temperature of the Earth’s atmosphere. The oxygen cycle also helps to maintain the Earth’s atmosphere by removing carbon dioxide from the air.

The phosphorus cycle begins with the weathering of rocks that contain phosphorus. This releases phosphorus into the soil, where it can be taken up by plants. Plants use phosphorus to produce food and energy. When plants die, the phosphorus they contain is returned to the soil.

Phosphorus can also be released into the environment through the activities of animals. When animals eat plants, they absorb the phosphorus that is contained in the plants. The phosphorus is then excreted in the animal’s feces.

Phosphorus can also be released into the environment through human activities. When we use fertilizers, we are adding phosphorus to the soil. When we burn fossil fuels, we are releasing phosphorus into the air.

The sulfur cycle begins with the release of sulfur from the Earth’s crust through volcanic activity and the weathering of rocks. This sulfur is then converted to sulfate by bacteria and archaea. Sulfate is the most common form of sulfur in the environment, and it is found in both water and soil.

Sulfate can be taken up by plants and incorporated into organic matter. When plants die, their organic matter is decomposed by bacteria and archaea, which release sulfur back into the environment. Sulfur can also be released into the atmosphere through the burning of fossil fuels.

In the atmosphere, sulfur can be converted to sulfur dioxide and sulfur trioxide by sunlight and other chemical reactions. These gases can then react with water to form sulfuric acid, which is a major component of acid rain.

Sulfuric acid can return to the Earth’s surface through rain and snow. It can also be deposited on land and water surfaces through dry deposition. Once on the ground, sulfuric acid can dissolve rocks and release sulfur back into the environment.