Calcium is an element that participates in various structures of living beings, bones, shells, cell walls of plant cells, calcareous eggshells, and acts on some physiological processes such as muscle concentration and blood coagulation in vertebrates.
The main sources of this element are limestone rocks, which, over time, release it to the middle. In the soil, it is absorbed by the vegetables and, through the food chains, passes to the animals. Tons of limestone are often used to correct soil acidity, notably in Brazilian savannas, a procedure that at the same time releases calcium for use by vegetation and animals.
In the oceans the calcium obtained by animals can be used to build their limestone coverings. With the death of these beings, the decomposition of the structures containing limestone - mollusk shells, foraminiferous coatings - at the bottom of the oceans, a process that contributes to the formation of limestone-containing land and rocks. Earth's crustal movements favor the outcropping of these lands, making calcium again available for use by living beings.