Also, many shallow marine environments are often associated with carbonate factory zones. In these zones, processes that remove the CO₂ from water to cause the bicarbonate ions to change into carbonate ions are important and support lime precipitation. Increasing temperature, intense evaporation, and mixing water that is high in CO₃ and low in calcium cations with seawater are some examples of processes that change bicarbonate ions to carbonate ions. Carbon dioxide is removed from the atmosphere by being dissolved in water and is turned into carbonic acid. The carbonic acid then weathers rocks, creating bicarbonate and other ions. Then the calcium carbonate is a precipitate from calcium and the bicarbonate ions that formed through organisms like coral, and then the carbon is stored in layers of limestone on the seafloor. In terms of geologic time, the composition of limestone has changed from calcite rich limestone to aragonite rich limestone. The presence of magnesium ions at certain concentrations inhibits the ability to precipitate calcite. Aragonite, however, has the same chemical formula as calcite but it is in a different crystal system that is much less prone to the magnesium preventing the precipitation of this mineral, which would prevent it from forming carbonate rocks. At times in geologic history where the Mg and Ca ratio were different, and the seas were more abundant in calcite and this was as a result of the high rates of seafloor spreading because of tectonic plate movement and action. The more spreading, the more the Magnesium gets removed, so more calcite is precipitated, and calcite will be more abundant than aragonite.
