Hi. very good question!
photosynthesis is the main mechanism through which CO2 is used up and O2 released. plants are only one example of organisms that perform photosynthesis and they do this with the help of chlorophyll, which is found in the organelles called chloroplasts. there are other organisms that have chloroplasts, and the biggest number of these organisms are green algae which are found in water bodies all over the earth. as you may know, most of the earth’s surface is covered with water. meaning that there is so much algae across the earth that provides oxygen for us all! whether we live on the desert, the north pole or in the middle of a forest!