It is an interesting question that my daughter asked me. Where did Oxygen come from? So I thought explain about it. I told her that we know that trees are take in carbon dioxide and release oxygen into the air during photosynthesis, but did all the oxygen in the atmosphere come from plants and trees?
Have you heard about Cyanobacteria? All the oxygen in the atmosphere has been produced not by trees but by single-celled bacteria called cyanobacteria. Cyanobacteria live in water, very often in colonies, and produce their own food through photosynthesis.
Cyanobacteria have been in existence for at least 3.5 billion years as scientists told. By developing the process of photosynthesis they released oxygen into the atmosphere, and this made it possible for larger life forms to emerge.
Even today, they are the major producers of oxygen. Even if all the trees in the world disappeared we would still have enough oxygen because of these bacteria in the sea. If they perished, so would we.
So what we should do? We should take care of the water. We should not waste water and we should take care of trees also. We have to save water in the sea by non polluting. We should not pour the industrial waste waters, or drainage water to the river and sea. If we take care about the purity of the water in the sea, river, lake etc. then we can keep the water very clean. Government should take initiative to make rule for not to pollute the water in the sea.