How was oxygen added to the atmosphere?

Answer 1

The biological era was marked by the simultaneous decrease in atmospheric carbon dioxide (CO2) and the increase in oxygen (O2) due to life processes. We need to understand how photosynthesis could have led to maintenance of the ~20% present-day level of O2.

The build up of oxygen had three major consequences that we should note here.

Firstly, Eukaryotic metabolism could only have begun once the level of oxygen had built up to about 0.2%, or ~1% of its present abundance. This must have occurred by ~2 billion years ago, according to the fossil record. Thus, the eukaryotes came about as a consequence of the long, steady, but less efficient earlier photosynthesis carried out by Prokaryotes.

Oxygen increased in stages, first through photolysis of water vapor and carbon dioxide by ultraviolet energy and, possibly, lightning:

H2O -> H + OH

produces a hydroxyl radiacal (OH) and

CO2 -> CO+ O

produces an atomic oxygen (O). The OH is very reactive and combines with the O

O + OH -> O2 + H

The hydrogen atoms formed in these reactions are light and some small fraction excape to space allowing the O2 to build to a very low concentration, probably yielded only about 1% of the oxygen available today.

Secondly, once sufficient oxygen had accumulated in the stratosphere, it was acted on by sunlight to form ozone, which allowed colonization of the land. The first evidence for vascular plant colonization of the land dates back to ~400 million years ago.

Thirdly, the availability of oxygen enabled a diversification of metabolic pathways, leading to a great increase in efficiency. The bulk of the oxygen formed once life began on the planet, principally through the process of photosynthesis:


6CO2 + 6H2O <--> C6H12O6 + 6O2

where carbon dioxide and water vapor, in the presence of light, produce organics and oxygen. The reaction can go either way as in the case of respiration or decay the organic matter takes up oxygen to form carbon dioxide and water vapor.

Life started to have a major impact on the environment once photosynthetic organisms evolved. These organisms fed off atmospheric carbon dioxide and converted much of it into marine sediments consisting of the innumerable shells and decomposed remnants of sea creatures.

While photosynthetic life reduced the carbon dioxide content of the atmosphere, it also started to produce oxygen. The oxygen did not build up in the atmosphere for a long time, since it was absorbed by rocks that could be easily oxidized (rusted). To this day, most of the oxygen produced over time is locked up in the ancient "banded rock" and "red bed" rock formations found in ancient sedimentary rock. It was not until ~1 billion years ago that the reservoirs of oxidizable rock became saturated and the free oxygen stayed in the air. The figure illustrates a possible scenario.

We have briefly mentioned the difference between reducing (electron-rich) and oxidizing (electron hungry) substances. Oxygen is the most important example of the latter type of substance that led to the term oxidation for the process of transferring electrons from reducing to oxidizing materials. This consideration is important for our discussion of atmospheric evolution, since the oxygen produced by early photosynthesis must have readily combined with any available reducing substance.

To simplyfy it, it is God creation. The earth is evolving but It is in His hand on how it works.

Answer 2

In the Proterozoic eon, 2500-543 mill. yrs ago, at the beginning of the eon, nothing lived on land, because, there was no oxygyn. All life was in the water. The primitive bacteria that existed there made oxygen from a result of them growing. The extra oxygen gathered up in the atmosphere over millions of years. About 2000 years ago, there was so much, it became permanent.

Answer 3

It is thought that Earth's atmosphere didn't have oxygen until the photosynthetic cyanobacteria began adding it to the atmosphere. There WAS, however, plenty of carbon dioxide for photosynthesis.

Answer 4

It depends on who you believe. Those who are religious would say it was added by God when he built the Earth in seven days. Scientists would say that photosynthetic bacteria first added oxygen to the atmosphere.

Answer 5

oxygen was added to the atmosphere by trees and plants because they send of oxygen to the air

Answer 6

The greatest producer of oxygen is blue-green algae.

Answer 7

Plants make oxygen.like we expell co2. They use co2. We use oxy. coincidense?

Answer 8

That "IS" the million dollar question >.

Answer 9

GOD added it.