The Carbon Cycle is probably better known as The Circle of Life. Since it is a continuous cycle, there is really no beginning of the cycle but we will start with the plants.

First the plants absorb carbon from the air through their leaves.
Then herbivores eat the plants and the plants give a percentage of their energy and their carbon to the herbivore.
Next carnivores eat the herbivores and that passes along energy and carbon as well.
Finally the carnivore dies, decomposes, and the carbon returns to the soil that eventually grows grass and other plants.

The atmosphere receives carbon from various sources but here are a couple:
- Burned fossil fuels.
- When animals exhale. (Including humans.)
- Believe it or not, volcanoes!
- Plant respiration. (When Plants "breathe" in, they also inhale oxygen so they exhale a portion of carbon dioxide.)

When you eat dirt for the first time and leave your family to build a shack in the woods