ABSTRACT
Calcium is the fifth most abundant element in the biosphere, after iron,
aluminum, silicon, and oxygen. Seawater contains approximately 10 mmol calcium per liter, that is approximately eight times higher than the calcium
concentration in the extracellular water of higher vertebrates. Freshwaters
contain calcium at concentrations of 1 to 2 mmol. In most soils, calcium
exists as an exchangeable cation in the soil colloids. It is taken up by plants,
where calcium concentrations are highest in the leaves, lower in the stems
and roots, and lowest in the seeds. In addition, calcium is the stuff of lime-
stone and marble, coral and pearls, seashells, and antlers and bones.
