A model of the carbon cycle typically shows that the amount of Earth’s carbon is constant. This is because carbon is continuously recycled through various processes, such as photosynthesis, respiration, decomposition, and combustion. While the forms of carbon (like carbon dioxide in the atmosphere, organic carbon in living organisms, and carbon in fossil fuels) can change, the total amount of carbon in the Earth system remains relatively stable over time.
So the correct response is: The amount of Earth’s carbon is constant.