1.1  Earth - our beautiful home

Earth is our beautiful home for all known life

The Earth’s Atmosphere is about 480 kilometres thick, however due to gravitational acceleration forces acting on various gases in the Atmosphere, most of the Atmosphere is pulled towards the Earth to within 16 kilometres of the surface. Therefore, the Air pressure measured in the Atmosphere decreases with rising altitude level away from the Earth’s surface. At sea level, air pressure is about 1 kilogram per square centimetre (14.7 pounds per square inch), and the Atmosphere has the highest density.            

Oxygen (O/O2) is necessary for most life on Earth, but the majority of Earth’s Atmosphere is not Oxygen. Earth’s Atmosphere is composed of about 78% Nitrogen (N), 21% Oxygen, 0.9% Argon (Ar), and 0.1% other gases. Trace amounts of Carbon Dioxide (CO2), Methane (CH4), Water vapor (H2O), and Neon (Ne) are some of the other gases that make up the remaining 0.1%.                  

Troposphere: the majority of the gas mass of the entire Earth’s Atmosphere is contained in the Troposphere at between around 75% to 80%. Most of the water vapor in the Atmosphere, along with dust and ash particles, are found in the Troposphere, explaining why most of Earth’s clouds are located in this layer. Temperatures in the Troposphere decrease with altitude. Presently, nearly all life above the Earth’s surface exists in the Troposphere.

A very large amount of life also exists in the Earth’s water bodies such as Oceans, Rivers, and Lakes.

REF: National Geographic – Atmosphere - https://www.nationalgeographic.org/encyclopedia/atmosphere/