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Where does Earth's oxygen come from?


How did all the oxygen get in our atmosphere and why don't we ever use it all up from breathing?

1716 day(s) ago

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David
Despite the common belief that vegetation is responsible for the presence of oxygen in the atmosphere, this is not stoichiometrically sound. There is simply not enough reduced carbon in the vegetation on the planet to balance out the vast amount of oxygen in the air. Put simply, the life cycle of plants is a part of the carbon cycle, but they are really dependent upon the atmosphere rather than the other way around. Burning off (oxidizing) all the plant life on earth would use up only a small fraction of all the oxygen in the atmosphere - less than 1%.

Chemistry must balance out its elements, that is what stoichiometry is. Trees cannot 'create' oxygen because matter is never created or destroyed, it merely changes form. When a tree absorbs CO2, it uses the carbon to build its structure and such, releasing the oxygen back to the air, but it does not 'create' it.

The vast ocean of oxygen in our atmosphere is a direct result of the fact that we have vast oceans of water. Water vapor is abundant in the atmosphere (where, incidentally, it is by far the most relevant green-house gas), and when it rises to the upper levels it is dissociated by high energy UV light into H2 and O2 gasses. The hydrogen gas is extremely light, and much of it boils into space, leaving the stable O2 behind to enrich the atmosphere.

Yet, it appears that there is no net loss of water from the earth due to the constant bombardment from micro-comets. These bodies are generally the size of houses, and the earth is peppered with tens of thousands of them daily. When they strike the atmosphere, they shatter into water vapor, adding water, and oxygen, to the ecosystem.

All life on earth is totally dependent upon the atmosphere, and it is dependent upon the supply of water on earth.

Posted 1041 day ago

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bjones
Most of the oxygen on Earth comes from plants and plant-like bacteria. Just as animals breathe oxygen and release carbon dioxide through respiration, plants breathe also, except they breathe carbon dioxide and release oxygen. Scientists speculate that in the beginning of the world, there was some carbon dioxide present and some single-celled organisms began to use it to create energy. Only later did animal life emerge after plants had created an oxygen-rich environment.

Eventually, enough oxygen and carbon dioxide was produced to become a major portion of the atmosphere. Today, the atmosphere is composed of 78% nitrogen, 21% oxygen, .93% argon, and .038% carbon dioxide. Other gases are also in the atmosphere such as neon, helium, methane, krypton, and hydrogen but the amounts are very small. These are known as trace gases.

Plants use carbon dioxide and sunlight to create energy in a process called photosynthesis. As a byproduct of photosynthesis, oxygen is released. Most of the oxygen from photosynthesis comes from the ocean. Some bacteria, known as cyanobacteria or blue-green algae, also create oxygen through photosynthesis. The other major source from the ocean is from plankton. Plankton are tiny plant-like organism that float around in water and serve as both an important source of oxygen and food. A lot of oxygen also is put into the atmosphere from trees.

Scientists do not know exactly how much oxygen comes from the ocean and how much comes from the trees on land. Some scientists believe that more than one-half of the oxygen comes from the ocean while other scientists say only about one-third of the oxygen comes from the ocean.

As you can see, plants are a necessity of life on Earth. Without any plants there would be no oxygen. If enough plant-life dies suddenly, we and the other animals would use more oxygen than is being produced. If the plants didn’t grow back, eventually all the oxygen would be used and we would no longer have anything to breathe.

Besides photosynthesis, a very small amount of oxygen is created when ultraviolet radiation from the sun breaks apart water molecules. This only accounts for about 2% of the oxygen while photosynthesis accounts for 98%.


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