Question

. Where is calcium carbonate found and how does it acts as a natural pH buffer?

Answer 1

Calcium carbonate:

The calcium carbonate is found in sea shells and the bones of sea creatures. And it is settled on layer of ocean. The pH level can be equilibrium with atmospheric $CO_2$. There is constant concentration of $CO_2$ in the water.

The limestone and calcium carbonate is present in the rocks, streams, lakes  is helps to maintain the constant pH in  the minerals present in the rock react with excess acid in the water.

When the acids or bases react with the calcium carbonate ,there is the excess change in the pH. The mixture of calcium carbonate ions in the water to prevent the damage in acid rain.