[1] The earth’s atmosphere is a layer of gases surrounding our planet and retained by gravity. It warms the earth, regulates temperature between night and day and protects life by absorbing ultraviolet solar radiation. The atmosphere of Earth is a layer. Our atmosphere contains 78% nitrogen, 21% oxygen, 0.9% argon and .03% carbon dioxide.
[2] Earth is considered to have had three atmospheres. At first, the atmosphere was light, captured from the solar nebula made up of hydrogen and helium. A solar wind and intense heat drove off this first atmosphere. After, the earth released gases, creating a second atmosphere rich in water vapour, carbon dioxide, methane and nitrous oxide, but devoid of oxygen. Thirdly, an oxygen-filled atmosphere was formed once bacteria and living organisms appeared on the planet.
[3] The first atmosphere of the earth was formed from outgassing. This process occurred when gases trapped in the interior of the earth were released by volcanoes. During differentiation, the chemical change of magma during its cooling process, massive volcanic activity occurred on the earth which resulted in the emission of gases by volcanoes. This led to the creation of this early atmosphere.
[4] Early on, the atmosphere was mostly made up of water vapour which in turn transformed to rain and ocean. The result led to a reduction in carbon dioxide and an increase in nitrogen and oxygen. It is considered that this oxidation process was an important factor in the increase of atmospheric oxygen. Once this gas was produced, ultraviolet light split the molecules, creating the ozone UV layer. This allowed colonization on the land, as evidenced from plant life that appeared approximately 400 million years ago. Through the process of photosynthesis, oxygen formation increased further. This occurred in ‘The biological era’.
[5] The appearance of photosynthetic organisms, such as algae, had a major effect on the earth’s environment. Algae survived on carbon dioxide and released oxygen into the atmosphere. That oxygen was absorbed by banded rocks and red beds. Once those rocks became saturated, 1 billion years ago, they freed oxygen into the air. Oxidation of minerals on land transferred oxidized substances to rivers and oceans. Mineral iron deposits recently discovered in alternating layers are called Red Beds and date back to 2 billion years ago. After another billion years, these red beds became exhausted and oxygen began to increase in the atmosphere. This increase initiated the development of species diversification and cell development.
[6] Oxygen makes up 20% of our earth’s atmosphere. A question that continues to puzzle scientists is how organisms were not damaged by UV radiation prior to the production of oxygen. The oceans provided limited protection. It is believed that stromatolites – algal mats – protected organisms. Some scientists theorize that early organisms had a protective UV-absorbing case. In any case, microorganisms began to diversify thanks to natural selection.
[7] By the end of the Permian period, 250 million years ago, oxygen levels had fluctuated dramatically and then dropped to 15 percent. The rapid changes in oxygen caused a growth in insect size, but finally led to a mass extinction of giant dragonflies and other animals. When comparing Earth to neighbouring planets, we observe that Earth is at the ideal distance from the sun so that water could form through gaseous, liquid and solid phases.
