In this article we will discuss about evolution of atmosphere, layers of atmosphere and structure of atmosphere
Evolution of Atmosphere
At the the time of origin of Earth due to its gravitation it was accompanied with hydrogen and helium. The primordial atmosphere of earth was lost due to high temperature because high temperature cause the expansion in prevailing atmosphere .
In early precambrian era atmosphere was thin , it was then enriched due to degassing caused by volcanic eruption. Cloud of gasses such as CO2, SO2, CH4,NO, N etc released due to eruption comprise of all gases present in atmosphere except oxygen and hydrogen.
After cambrian period evolution of green plants reduced CO2 and increased oxygen concentration by the process of photosynthesis. Another process that increased oxygen is photolysis of water vapour.
CO2 concentration increased at the beginning of industrialization . CO2 was 280 parts per million in 1770s. Presently about 420 parts per million. The annual release of CO2 has increased from 5 billion tons to 35 billion tons .
Layers of Atmosphere
Troposphere- Average height of troposphere is about 17 km accept high temperature at equator due to vertical sun rays causes expansion of air extending it more than polar latitudes. The height of troposphere increases towards northern hemisphere during summer solstice and towards southern hemisphere during winter solstice
It is called zone of mixing because all weather phenomena remained confined to troposphere . Troposphere follows lapse rate that is rate at which temperature decrease with increase in elevation .Upper layer of the troposphere at equator has lesser temperature than upper layer of the troposphere at poles.
Stratosphere- It extends up to 50 km . Ozonosphere extends up to 35 km. Oxygen is dissociated and converted in nascent atom by ultravoilet radiation . Nascent atoms then combines with oxygen to form ozone if being a weaker molecule get further dissociated as O2 and O called as Chapman’s cycle or ozone cycle.
The interaction of UV rays with ozonolysis with oxygen and ozone restricts UVA and UVB in stratosphere.
Mesosphere- It is a transitionary layer between lower atmosphere and upper atmosphere. Temperature decreases with elevation. It extends up to 80 km.
Ionosphere- The high temperature and ionising radiations are responsible for converting gaseous atoms into ions . Ionosphere therefore dissociates after sunset. It is further divided as D layer, E layer again dissociates after sunset and reflects medium frequency radiowaves then F layer partially dissociates reflect high frequency radiowave.