Which step in the carbon cycle describes how carbon enters the atmosphere?

In the carbon cycle, the step that describes how carbon enters the atmosphere is the combustion of fossil fuels. This process releases significant amounts of carbon dioxide, a greenhouse gas, directly into the atmosphere as fossil fuels such as coal, oil, and natural gas are burned for energy, transportation, and electricity generation. This addition of carbon dioxide from human activities has been a major contributor to the increase in atmospheric carbon levels, which is a key factor in climate change.

While other processes also play a role in the carbon cycle, they either do not directly emit carbon into the atmosphere or represent carbon being absorbed or utilized by living organisms. The absorption of carbon dioxide by plants is a part of photosynthesis, where plants take in carbon dioxide rather than release it. Exhalation by animals during respiration does release carbon dioxide; however, it is a smaller contribution to the overall atmospheric carbon compared to combustion. The decomposition of dead organisms also releases carbon back into the soil and atmosphere, but it is typically a slower process and less impactful in the context of rapid carbon emissions compared to combustion activities.