The primary Earth’s atmosphere consisted mainly of water vapor, hydrogen, and ammonia. Under the influence of the sun’s ultraviolet radiation water vapors decomposed into hydrogen and oxygen. Hydrogen in considerable part vaporizes in space, while oxygen reacted with ammonia to form nitrogen and water. At the beginning of the geological history, the Earth through the magnetosphere, which isolated it from the solar wind, created its own secondary carbon atmosphere. Carbon dioxide came out from the depths under intense volcanic eruptions. With the advent of green plants in the late Paleozoic era oxygen began to enter the atmosphere as a result of the decomposition of carbon dioxide during photosynthesis, and the composition of the atmosphere has taken a modern look. The modern atmosphere is largely a product of living matter of the biosphere. The full update of the planet’s oxygen by living matter occurs in 5200-5800 years. All its weight is assimilated by living organisms for about 2 thousand years, while carbon dioxide for 300-395 years.
During the initial radioactive heating of young Earth, the emission of volatile substances liberated to the surface, which formed the primary ocean and the atmosphere. It can be assumed that the primary atmosphere of our planet by composition was similar to the composition of the meteorite and volcanic gases. In some extent, the primary atmosphere (CO2 content was 98%, argon – 0.19%, and nitrogen – 1.5%) was similar to the atmosphere of Venus, a planet that in size is the closest to our planet.
The primary Earth’s atmosphere had a restorative character, and was virtually devoid of free oxygen. Only a small part of it occurred in the upper atmosphere as a result of the dissociation of carbon dioxide and water molecules. Currently it is confirmed that at a certain stage of development of the Earth, its atmospheric carbon passed into the nitrogen-oxygen. However, the timing and nature of the transition remains unclear.
Currently, there is data on the presence of free oxygen in the Precambrian. The presence of highly oxidizing iron compounds in red iron ores of Precambrian indicates the availability of free oxygen. The increasing of its content throughout the biosphere history was determined by plotting the corresponding models of varying degrees of reliability.
According to scientists, the atmospheric composition changed continuously and was regulated both by processes like mantle degassing, and physical and chemical factors, which took place on the Earth, including cooling and thus decrease of the temperature of the environment. Chemical evolution of the atmosphere and hydrosphere in the past was closely related to the balance of its substances.
The primary Earth’s atmosphere consisted mainly of water vapor, hydrogen, and ammonia. Under the influence of the sun’s ultraviolet radiation water vapors decomposed into hydrogen and oxygen. Hydrogen in considerable part vaporizes in space, while oxygen reacted with ammonia to form nitrogen and water.