What happened to the carbon that poisoned the atmosphere on earth?

I believe that the answer is that Carbon dioxide (CO2) is still, building up in the atmosphere because we are still burning fossil fuels (coal, oil and natural gas) which emits CO2, and we are still cutting down trees which will not remove CO2 from the atmosphere. The natural carbon cycle is unable to remove all the extra CO2, maybe only 60% of it, so the carbon is building up in the atmosphere and causing global warming.