Carbon Cycle : CO
2 is 0.03% in atmosphere, which is utilized by producers in photosynthesis for making food.
From producers, it goes to consumers and then through decomposers into atmosphere.
The producers, consumers & decomposers may be converted into fossil fuel (petrol, coal etc.) or form carbonate rock after death.
By way of respiration the biotic component returns CO
2 to atmosphere.
CO
2 may get dissolved in water. The lime rocks also contribute to CO
2 in water. The aquatic producer use this CO
2 for photosynthesis and return it by respiration.
By combustion of fossil fuel & also by volcanic activity, CO
2 is returned to the atmosphere.