CALCIUM CYCLE: CHARACTERISTICS, STAGES AND IMPORTANCE - CHEMISTRY - 2025

The calcium cycle is the circulation and storage on Earth of this element, encompassing living beings, the lithosphere and the hydrosphere. It is a sedimentary biogeochemical cycle in which calcium circulates as an alkaline earth soft metal, lacking a gaseous stage.

The stage of greater circulation of calcium is the biological one, as it is consumed by living beings and used in their structures and metabolism. Once living beings are dead, calcium is reintegrated into the physical environment as part of the soil and the seabed.

Calcium. Source: Pumbaa (original work by Greg Robson) / CC BY-SA 2.0 UK (https://creativecommons.org/licenses/by-sa/2.0/uk/deed.en)

There are extensive deposits of shells and bones especially on the seabed and in the great lakes. These structures mix with sediments and are covered by successive layers over millions of years.

The lower layers of sediments are subjected to high pressures forming sedimentary rocks that are then exposed to the surface due to terrestrial geological processes. Exposed rocks are subjected to weathering and erosion, releasing calcium that is integrated into the soil or is washed away.

In the soil it is absorbed mainly by the roots of plants and in the sea by phytoplankton and other organisms. Calcium is used for different structural and metabolic purposes, for example the manufacture of shells.

The calcium cycle is important since it allows this element to be available in its different stages, fulfilling various functions. Thus, being part of the structure of living organisms, participates in the formation of the terrestrial relief, regulates the pH of soils and waters and serves as raw material for human industry.

General characteristics

- The calcium

Calcium (Ca) is an alkaline earth soft metal with atomic number 20 and atomic mass 40.078, whose ordinary state is solid. Forms oxides that act as strong bases, reacting violently when in contact with acids.

- Your cycle

Calcium fulfills a sedimentary-type biogeochemical cycle, since it lacks a gas phase and the largest reserves are in the lithosphere. It is closely related to the carbon, water and phosphorus cycles.

Rock erosion

The cycle develops from the weathering and erosion of calcareous rocks that release the calcium that is deposited in the soil. Likewise, it can be washed away dissolved in runoff water into rivers, lakes and oceans.

When rainwater comes into contact with atmospheric CO2, it forms H2CO3 that dissolves limestone rock, releasing Ca2 + and HCO3-. On the other hand, the CO2 carried by the rainwater transforms the insoluble carbonate into soluble bicarbonate.

Absorption and use by living beings

Calcium (Ca2 +) in the soil is absorbed by plants and in water bodies by aquatic organisms. In the body, calcium fulfills different metabolic functions and when organisms die, it returns to the physical environment, carried away by runoff water into rivers, lakes and oceans.

Rock formation

Animal skeletons (internal and external or shells) are deposited on the seabed as part of the sediments. The sediment layers are covered and compacted over millions of years to form calcareous rocks.

Calcareous rocks. Source: Ferdous / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Later diastrophic processes (cracks and upward movements of the earth's crust) expose the rocks to the surface. In this way the cycle is closed, because the rocks are again weathering (action of the climatic elements) and are weathered and eroded.

Stages of the calcium cycle

The stages that calcium goes through in its storage and circulation cycle are given by the compartments in which these processes occur. These are the crust and part of the earth's mantle (lithosphere), bodies of water (hydrosphere) and living organisms.

- Geological stage

In the geological stage, compartmentalized in the crust and mantle, it is where the greatest amount of calcium storage is found. Calcium is the fifth most abundant element in the lithosphere, constituting 3.5% of the earth's crust.

It is found forming part of rocks such as limestone, dolomite, marl and marble, while limestone and dolomite form huge mountain ranges throughout the planet. In the same way, it is part of other natural compounds such as gypsum and alabaster (calcium sulfate).

In mineral form, it is obtained as calcium carbonate (CaCO3) from calcite, dolomite and other crystalline forms such as aragonite.

Limestone

It is a very abundant type of sedimentary rock originating from ancient marine or lacustrine deposits (lakes), composed of 99% calcium carbonate. These rocks form horizontal strata or deformed by diastrophic movements and their weathering gives rise to neutral to basic soils (pH 7 or higher), rich in calcium.

Dolomite

It consists of a sedimentary rock formed in shallow marine deposits by a chemical substitution reaction. In this case, magnesium participates in the mineral conformation, forming dolomite or calcium magnesium carbonate (CaMg (CO3) 2).

Margas

They are sedimentary rocks formed by 1/3 to 2/3 of calcium carbonate and the rest of clays. These rocks survive in dry areas, since they are very susceptible to water erosion.

Marble

If limestone rocks are subjected to high temperatures and pressures in deep layers of the earth's crust, marble is formed. This is a very compact metamorphic rock with a high degree of crystallization.

- Hydrological stage

Calcium is dissolved in rivers, lakes and oceans as calcium chloride (being the most abundant ion in this medium) and calcium carbonate. In the oceans, calcium carbonate (CaCO3) is stable at depths less than 4,500 m.

Calcium in this medium is found in living organisms and in limestone deposits on the seabed. This is the depth limit of carbonate compensation, after which CaCO3 dissolves and does not form limestone deposits.

- Biological stage

Movement of calcium from the soil to the roots. From the xylem to the leaves of the plant. Dhagerty / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

At this stage, the calcium cycle reaches its greatest circulation, being vital for living beings because as a Ca2 + ion it is part of the exchange mechanisms of cell membranes. On the other hand, it is an essential constituent of bones, teeth, eggshells and shells.

Calcium shells in bivalves. Source:

In this way, calcium circulates in the biosphere and when organisms die, it returns to the sediments to form new rocks over time.

The human being

An outstanding element of the biological stage of the calcium cycle is the role of human beings in using this element as a raw material. This element is extracted, transported and used in large quantities in different ways.

In open pit mines, limestone is extracted to use it as a construction element or to grind it and use it as an industrial raw material. The shells are also ground to prepare fertilizers and other products.

The shells of foraminifera and mollusks

The shells of these animals are formed from calcium carbonate, crystallized as calcite or aragonite. These are two mineral forms of the same composition (CaCO3) but which crystallize differently.

Mollusks form their shells from a liquid form of calcium secreted by specialized cells. The innermost layer of the shell is the nacre formed of aragonite crystals mixed with the conchiolin protein.

Importance

The circulation of calcium, forming its characteristic cycle, is essential to make this element available to living beings. Thanks to the processes that release calcium from rocks and make it circulate, life exists as we know it.

- Essential element for life

Calcium is essential for life, as it is both a structural and a metabolic element. Structurally, it is a fundamental part in the conformation of both internal and external skeletons.

In bony animals, calcium is the main component of the bones (internal skeleton), also of the teeth. In foraminifera (protists) and mollusks (snails and bivalves) it is the main ingredient for the formation of the external skeleton, that is, the shells.

Metabolism

Calcium is a transport agent in cell membranes, so it plays an important role in metabolism. In cell membranes there are calcium channels that allow the passive entry of this element into cells.

Calcium channels. Source: Ulrich Förstermann - Elsevier GmbH / Public domain

This regulates the relationship of calcium concentrations between the inside and outside of the cell, activating different metabolic processes. For example, these mechanisms are essential for the functioning of the nervous and muscular system and therefore play a relevant role in cardiac function.

- Food and health

From the human point of view, the calcium cycle makes it possible to make this element available to food and human health. Above all it is essential in the production and preparation of dairy foods for children.

Similarly, its ingestion for medicinal purposes is used in the treatment of calcium deficiency diseases such as osteoporosis. This bone-weakening disease is especially serious in older people, especially in women.

- The pearls

When a foreign body invades the oyster, it covers it with mother-of-pearl and thus a pearl is formed. Pearls reach high values ​​in the jewelry market worldwide.

- Industrial raw material

Limestone is used industrially for various purposes, for example the manufacture of cement. Also these stones are used directly as a building material, due to their easy carving.

Furthermore, calcium is used as a deoxidizer and reducing agent in different processes, especially in the metallurgical industry.

Lime

As quicklime, also called building lime, they are calcium oxides that are used as a binder and coating in construction. In the same way, it is used in the manufacture of soap, paper, glass, rubber and in leather tanning.

Likewise, it has various uses in the food industry and in water treatment. While as slaked lime or calcium hydroxide, it is also used in industry and agriculture.

- Soil pH regulation

The content of calcium oxides in the soil affects the regulation of pH. In agriculture quicklime is used as an agricultural amendment to reduce the acidity of soils and also as a fertilizer.

- Calcareous water or hard water

When water circulates in environments rich in calcium and magnesium, it dissolves salts of these elements and is known as calcareous or hard water. The water quality limit is 120 mg CaCO3 / liter, above which the water is considered to be hard.

Water with high calcium content can cause health problems, especially related to the cardiovascular system. In addition, hard water produces calcareous deposits in the pipes that obstruct circulation.

- Calcareous caves and aquifers

In calcareous rocks, hydric erosion often forms underground cave systems with interesting internal configurations. Among these, the formation of stalactites and stalagmites stands out, due to the calcium carbonate deposits from the leaks on the roofs of these caves.

These calcareous systems also perform the filtering function of groundwater due to its porosity, forming aquifers.

References

1. Calow, P. (Ed.) (1998). The encyclopedia of ecology and environmental management.
2. Christopher R. and Fielding, CR (1993). A review of recent research in fluvial sedimentology. Sedimentary Geology.
3. Margalef, R. (1974). Ecology. Omega editions.
4. Miller, G. and TYLER, JR (1992). Ecology and Environment. Grupo Editorial Iberoamérica SA de CV
5. Odum, EP and Warrett, GW (2006). Fundamentals of ecology. Fifth edition. Thomson.