What makes the carbon cycle so important? what step in the carbon cycle makes carbon readily available for plants?

Without the carbon cycle we wouln't have air to breathe, we would die due to the lack of air.

Plants use carbon dioxide and sunlight to make their own food and grow. The carbon becomes part of the plant. Plants that die and are buried may turn into fossil fuels made of carbon like coal and oil over millions of years. When humans burn fossil fuels, most of the carbon quickly enters the atmosphere as carbon dioxide.