Which process is major source of oxygen released into the atmosphere?

The correct answer is Photosynthesis. It is a process found in plants that enables them to turn light into chemical energy. Luckily for us, the the waste product for plants in this is Oxygen which is released into the atmosphere. The more plants there are the more oxygen there is. That's just one more reason why cutting down the rainforests is extremely dangerous for the future of humanity on Earth.