There is a continuous supply of calcium ions into waterways from rocks, organisms, and soils.[1][2] Calcium ions are consumed and removed from aqueous environments as they react to form insoluble structures such as calcium carbonate and calcium silicate,[1][3] which can deposit to form sediments or the exoskeletons of organisms.[4] Calcium ions can also be utilized biologically, as calcium is essential to biological functions such as the production of bones and teeth or cellular function.[5][6] The calcium cycle is a common thread between terrestrial, marine, geological, and biological processes.[7] Calcium moves through these different media as it cycles throughout the Earth.