If humans and all other animals are constantly producing carbon dioxide, and is a very stable gas, why does it make up only a tiny percentage of the earths atmosphere?

Could it be that something is using the CO2. Plants use CO2.

That is a good answer, but it does seem too simple to me. But maybe it really is a simple question.

I might just add that when plants use CO2 they produce sugars and oxygen. And since oxygen is abundant in the atmosphere then perhaps the concentration of oxygen remains unchanged relative to CO2?

Here is a site that is VERY good reading. Scroll down to the section that is titled "concentration." Note that 95% of the CO2 emitted is caused by sources other than humans which accounts roughly for the small changes in CO2 concentration. Note also that there is a very small (but measurable) concentration change in CO2 between spring and winter months in the northern hemisphere which is assumed to be the fluctuation caused by spring flowers versus winter's loss of photosynthesis. Good reading.

http://en.wikipedia.org/wiki/Carbon_dioxide_in_the_Earth%27s_atmosphere

why are you so smart

how do the products of their decomposition compare

Carbon dioxide (CO2) is indeed produced by various sources, including human activities, as a byproduct of respiration. However, the concentration of CO2 in the Earth's atmosphere is relatively low compared to other gases. The reason for this lies in the balance between carbon dioxide sources and sinks.

There are natural processes such as photosynthesis, where plants absorb CO2 and convert it into oxygen through the use of sunlight. Additionally, the oceans act as a giant sink for CO2, absorbing a significant portion of it from the atmosphere. These natural processes help to regulate and maintain the carbon dioxide levels in the atmosphere.

To calculate the exact percentage of CO2 in the Earth's atmosphere, you can refer to scientific data. The most commonly used measurement is parts per million (ppm), which represents the number of CO2 molecules per million air molecules. As of 2021, the concentration of CO2 in the atmosphere is approximately 415 ppm, or 0.0415%.

To find this information, you can visit reliable sources such as scientific organizations, government agencies, or international climate monitoring bodies. These organizations often publish regular reports and provide accurate data on atmospheric CO2 levels.

Remember that CO2 concentration values can vary over time due to factors like human activities, natural climate variability, and long-term climate trends. Continuous monitoring and research help scientists understand these changes and their potential impacts on the environment.