They were the oldest organisms called Stromatolites which did not need oxygen themselves but produced it by photosynthesis.
Volcanoes
Well, oxygen supports burning. Fire needs fuel, oxygen and a spark or another source of ignition. So the more oxygen there is, the faster your substance will burn! There is 21% oxygen in air, and when you have an atmosphere of oxygen, it can go to quite high concentrations. So sulphur will burn in an atmosphere which has a higher oxygen content.
Oxygen was released from Precambrian rocks. cynobacteria were the first organisms to produce oxygen 2.5-3 billion years ago
oxygen producing organisms
If you mean how does it come to be in the atmosphere, oxygen is released into the atmosphere by plants, mostly by phytoplankton in the ocean. I you mean how is oxygen created in the first place, it is the result of lighter elements being fused together in the cores of stars.
Oxygen came before Eukaryotes and this is known due to the fact that Eukaryotes need oxygen to live.
oxygen producing organisms
oxygen
Plants
Plants
The oxygen in water is the oxygen that is released into the atmosphere.
Green Plants
Oxygen in the atmosphere, and UV-C from the Sun.
cyanobacteria
photosynthesis by cyanobacteria
Plants and trees, they convert it to oxygen
plant-like plankton in the ocean put out most of the oxygen in the atmoshere as a waste-product of photosynthesis.
plant-like plankton in the ocean put out most of the oxygen in the atmoshere as a waste-product of photosynthesis.