Phytoplankton and Forests bring us Oxygen

It's not just Phytoplankton that brings people oxygen to breathe. I believe the biggest source of oxygen is from trees in forests. It is one reason people have a sense of well being when in a forest because their bodies sense the oxygen there. Trees and plants take Carbon dioxide and use it and convert it to oxygen we take oxygen and breathe out carbon dioxide. When you have too many cattle and people and then cut down all the forests people are less able to breathe because forests give us oxygen. So, a component of all this is too many people and cattle and not enough trees left alive here on earth. By cutting down all the forests we all move towards suffocation.

It isn't just phytoplankton even though this is a problem too. For us on the land a much greater problem (especially inland from the seas) is cutting down too many forests and reducing oxygen on land in this way too.

It is one reason why people should plant forests and move underground so they can still have oxygen to breathe instead of cities that rob people of oxygen to breathe because there aren't enough trees there.

So then cities encourage suffocation in the long run because forests are often cut down to build those cities.