Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone, which contains both of those minerals) and is the main component of pearls and the shells of marine organisms, snails, and eggs.
An ordinary breath for a 70-kg adult is about 500ml of air. We call this the tidal volume. Since oxygen is 21% by volume of air, then the volume of oxygen inhaled is about 105ml. The density of pure oxygen at sea level is 1.43kg per cubic metre.
Humans normally breathe approximately 5 to 6 liters of air per minute through the nose when at rest, but use the mouth as the primary passageway for air when ventilation is increased to approximately 20 to 30 liters per minute during exercise. ACE's Essentials of Exercise Science for Fitness Professionals, p. 8.