FORMATION OF  ATMOSPHERE 

our atmosphere can be thought of as a complex chemical factory. let's look at how it formed from the beginning of the earth(4.9 billion years ago). the earth is formed by collapsing the huge spinning cloud of hot interstellar gas and dust. it's a rocky volcanic world that has separated its interior into thin low density crust, a thicker silicate mantle, and a high-density partially iron core. this was a plane with an atmosphere of nitrogen and oxygen and also water vapor. 

source: https://www.britannica.com/topic/evolution-of-the-atmosphere-1703862

 3.9 billion years ago the atmosphere is still toxic and the earth's oceans come from both internal and external sources of water. carbon dioxide and ammonia gas dissolved in water and the earth's early oceans quickly become a sink for dissolving enormous quantities of these compounds removing most of them from the atmosphere. due to volcanoes, carbon dioxide is added to the atmosphere continuously. many scientists believe that the result was an archean atmosphere that could have had abundant hydrogen and methane and much less free oxygen. so the scientist refers to this as the reducing atmosphere.

source: https://www.britannica.com/topic/evolution-of-the-atmosphere-1703862

Experiments dating back to 1950 have shown that when liquid water is in contact with such an atmosphere and is exposed to energy sources like lightning or ultraviolet radiation, the result can be the formation of abundant organic molecules including simple amino acids and other essential building blocks of life.

At the beginning of the archean period, the atmosphere had little free oxygen and likely kept the surface quite hot because of the presence of abundant greenhouse gases such as carbon dioxide, methane water vapors, and other gases. the carbon dioxide is still pumping from the volcanoes. the salinity of oceans increases due to the erosion from the continents to the oceans and also it helps to neutralize the acidity of the ocean water.

source: https://earthhow.com/archean-eon/

 only life found on earth is single-celled bacteria (cyanobacteria) in the oceans. those bacteria were used to produce glucose through the processes of photosynthesis. the use of carbon dioxide from the seawater and the sunlight to produce glucose. the side product is oxygen. so that helps to increase the oxygen level in seawater and the atmosphere. for the next two billion years the oxygen level has risen. there the atmosphere cooled and become more oxidizing due to the high oxygen concentration. this high oxygen concentration oxidizes the essential gases for greenhouse effects such as carbon dioxide and methane etc. due to the lack of greenhouse gases the temperature of the atmosphere goes down. 

The cryogenic period has started. the word Cryogenian refers to the cold birth in greek. 

source: https://earthlyuniverse.com/cryogenian-glaciations-birth-animals/

This is 720 million years ago. still, the carbon dioxide released by the volcanoes in huge amounts into the atmosphere. when the continents are apart, many rocks have been exposed and those rocks absorb the carbon dioxide in the atmosphere. the earth began to cover with ice. this glaciation occurred just after the great oxidation event.

 as the earth covers with oxygen, the rocks cannot absorb the carbon dioxide pumps from the volcanoes. therefore carbon dioxide fills in the atmosphere. then the temperature starts to rise and ice starts to melt down. oxygen concentration also starts to rise through the series of reactions. due to the radion of the sun, the ozone has started to form.

source: https://earthlyuniverse.com/cryogenian-glaciations-birth-animals/

This was the beginning of the formation of the ozone layer. the ozone layer protects the earth from the radiation that comes from the sun. For over 120 million years the ozone layer thickening.

 The Permian extinction is the first massive extinction. this nearly leads to the end of all life on earth. so it is called the great dying. 96% of ocean dwellings and 70% of land-dwelling species have died. this extinction is caused by the filling of sulfur dioxide in the atmosphere and the carbon dioxide from the Siberian eruption. Scientists hypothesize that this massive volcanic eruption leads to dramatic changes in the atmosphere. due to the cloudy conditions of the atmosphere sunlight couldn't reach the earth and the acidity level of seawater changed and the oxygen level also changes.

After millions of years from the extinction, the atmosphere becomes normalized and the temperature stabilizes. the acid rains also neutralize. 47 million years ago the temperature is much like today and the duration of a day extends up to 24 hours. plants have evolved to have C4 photosynthesis. then the plants use carbon dioxide and water vapor to produce glucose as fuel. the fore this helps to decrease the carbon dioxide in the atmosphere.

At the end of the 19th century, scientists realized that earth is a habitable oceanic world only because of the influence of two relatively minor but critically important atmospheric gases, water vapor, and carbon dioxide. without those two the oceans would remain as solids due to the freezing of water. with the improvement of meteorological instruments and balloons, researchers can make direct measurements of the temperature and pressure of the atmosphere up to very high altitudes. early they discovered that there are two layers in the atmosphere and they named the lower part the troposphere and the upper part the stratosphere. with the development of science and technology, they were able to find out the five layers of atmosphere instead of the two layers.

source:https://cdn1.byjus.com/wp-content/uploads/2020/10/atmospheric-layers.png 

The five layers of the atmosphere are,

1. Troposphere(0-10 km)
2. Stratosphere(10-30 km)
3. Mesosphere(30-50 km)
4. Thermosphere(50-400 km)
5. Exosphere(>400 km)

The troposphere is the layer responsible for climatic changes. Temperature and oxygen concentration decreases with the altitude. The gas composition of the atmosphere is

• Nitrogen 78%
• Oxygen 21%
• Argon 0.9%
• Carbon dioxide 0.07%

Those are the main gases found in the atmosphere. There are water vapors in the atmosphere which range from 1-4% by volume in the lower atmosphere. The next important and valuable part of the atmosphere is the ozone layer which protects the earth from UV radiation. The temperature of the earth depends on three factors. Those are the amount of sunlight received by the earth, the amount of sunlight the Earth reflects, and the atmospheric retention of the radiated heat.

Carbon dioxide, water vapors, methane, and chlorofluorocarbons absorb the heat energy from the sunlight. Due to these gases, the earth is 40 Celcius degrees warmer than where it could be without these gases. This effect is known as the greenhouse effect. The increase of greenhouse gases such as methane CFC etc causes the depletion of the ozone layer.