The average human exhales around 2.3 pounds of CO2 per day [0]. That means that in a lifetime (70 years), a human breathes out around 59,000 pounds of CO2, whic

The average human exhales around 2.3 pounds of CO2 per day [0]. That means that in a lifetime (70 years), a human breathes out around 59,000 pounds of CO2, which is 608,000 moles of CO2 or 3.7 * 10^29 atoms of CO2 [2]. By your gigaton number then there will be on average less than one atom of his CO2 production in 50,000 years [3]. What happens if we consider total carbon footprint instead? Various sources cite around 20 metric tons per year as the average carbon footprint for someone living in the US. That's about 120 times higher than the amount exhaled, and since log(a*b) = log(a) + log(b) we can just add 3540 years [4] to our above calculation ~= 54,000 years. So above a millennium, but much less than a billion years. [0] https://slate.com/news-and-politics/2009/08/are-you-heating-the-planet-when-you-breathe.html https://slate.com/news-and-politics/2009/08/are-you-heating-... [1] https://www.wolframalpha.com/input/?i=59000+pounds+%2F+mass+of+carbon+dioxide https://www.wolframalpha.com/input/?i=59000+pounds+%2F+mass+... [2] https://www.wolframalpha.com/input/?i=608,000+moles+to+atoms https://www.wolframalpha.com/input/?i=608,000+moles+to+atoms [3] https://www.wolframalpha.com/input/?i=-log_(739%2F740)(3.6614616%C3%9710%5E29) https://www.wolframalpha.com/input/?i=-log_(739%2F740)(3.661... [4] https://www.wolframalpha.com/input/?i=-log_(739%2F740)(120) https://www.wolframalpha.com/input/?i=-log_(739%2F740)(120)