What is the significance in human life of those algae that form phytoplankton?

Phytoplankton has an essential function in our biosphere. Many people believe that plants regulate most of the oxygen, but in reality this is not the case. The bulk of oxygen is obtained during photosynthesis of phytoplankton. Although it has a microscopic size, its volume is very large. If all phytoplankton disappeared, then life on our planet would begin to disappear. Most living organisms are adapted to 0.03% carbon dioxide and 21% oxygen. If the composition of the air changes, most of the animals would become extinct.