Atomosphere

We are living at the very bottom of an invisible ocean which is called the atmosphere, which is a layer of gases that are surrounding our planet. Oxygen and Nitrogen types of gases which account for 99 % of the gases which are there in air which is also called dry air  along with carbon dioxide and helium and  argon, neon and even other gases which are making up a minute portions.

The atmosphere not only protects our environment from the dangerous things which are present in the planet earth but along with it it also provides us a layer which is responsible for balancing the temperature of our planet earth. The vapours of Water and the dust are also part of the atmosphere of Earth. Other planets and satellites like moons have very different atmospheres and when we observe that some have no atmospheres at all.

The bottom is said to be 30 kilometers  and 19 miles of the atmosphere contains around 98 percent of its mass. The air which is in the atmosphere is much thinner at high altitudes. The atmosphere is not in space.

Scientists say that there are many gases in our atmosphere that were ejected into the air by early volcanoes as well. At that time there would have been very little or in fact no free oxygen that surrounded the Earth. The oxygen which is Free oxygen consists of oxygen molecules not attached to another element like carbon to form carbon dioxide or hydrogen to form water.

The oxygen which is free oxygen may have been added to the atmosphere by primitive organisms which is  probably bacteria during photosynthesis. Photosynthesis is said to be a process where a plant or other autotroph is used to make oxygen and oxygen from carbon dioxide and water. Later on more complex forms of plant life were added with more oxygen to the atmosphere. To accumulate the oxygen in today’s atmosphere probably took millions of years.

Pressure 

The pressure of Atmospheric at a particular location is the force per unit area which is perpendicular to a surface determined by the weight of the vertical column of atmosphere above that location. On the planet Earth the units of air pressure are based on the internationally recognized standard atmosphere defined as atm, which is defined as 101.325 kPa that is 760 Torr or 14.696 psi. It is usually measured with a barometer.

Pressure of Atmospheric decreases with altitude increasing due to the diminishing mass of gas above. The pressure in the atmosphere which depends on the height defined as the one which is declined by the factor which is defined as e  that is an irrational number with a value of 2.71828 is known as the scale height and is denoted by capital H. For an atmosphere that has a uniform temperature for it the height which is scale height is directly proportional to the temperature and it is inversely proportional to the product of the molecular mean mass which of dry air and the local acceleration of gravity at that specific location. For atmospheres such a model, the pressure declines totally with increasing altitude. 

Scape of Atmosphere

The gravity of the Surface differs significantly among the planets.see the escape velocity distance from the Sun then we will see that it determines the energy available to heat atmospheric gas to the point where some fraction of its molecules' thermal motion exceeds the planet's. Thus if we see distant and cold Titan or Triton, to retain their atmosphere Pluto is able to despite their relatively low gravities.

there will always be some air that will be fast enough to produce a slow gas of leakage into space. The molecules which are Lighter molecules in nature move faster than the heavier molecules as we already know, along with the same thermal energy which is kinetic, and so the gases which are of low molecular weight are lost more easily than those of high molecular weight. It is said that the Mars and Venus planets may have lost much of their water when and  after being photo dissociated into gases like oxygen and hydrogen by solar ultraviolet radiation the hydrogen escaped. 

Composition of Atmosphere 

The atmosphere which is said to be the initial atmospheric composition of a planet is related to the temperature and the chemistry of the local solar nebula during planetary formation of interior gases which are subsequent. The atmosphere which is the original atmosphere started with a rotating disc of gases which later collapsed to form a series of spaced rings that condensed to form the planets. The planets such as Mars and Venus are primarily composed of carbon dioxide and with small quantities of nitrogen, oxygen, argon and traces of other gases as well.

The earth's composition in the atmosphere is largely governed by the by-products of the life that it sustains. The air which is Dry from Earth's atmosphere contains around 20.95% oxygen, 78.08% nitrogen, 0.93% argon, 0.04% and other gases which are said to be noble by volume, but generally if we see then a variable amount of vapours of water is also present on average about 1% at level of sea.