What factors could cause changes in the carbon dioxide and oxygen gas levels of Earth’s atmosphere?

On Earth, human activities are changing the natural greenhouse. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO2). This happens because the coal or oil burning process combines carbon with oxygen in the air to make CO2.

the three components of a nucleotide are the nitrogenous base, the phosphate group and the five-carbon sugar.