The history of the Earth indicates that it was not at all suitable for any form of life long after its creation . Lack of water and oxygen,high temperature,continous bombardments by meteorites , and tens of other factors made life for any creature impossible.But after millions of years a more suitable environment developed following the processes of degassing,and the solidification and formation of the Earth's crust which occured at the same time.From then on some biological processes like photosynthesis played a decisive role in providing a more friendly environment for life to develop , in such a way that the atmosphere and the living condition on the Earth is sharply distinctive from that of other planets.
As mentioned before,continous bombardment by meteorites was one of the factors which had quite decisive effects on the planet Earth. The bumpy surfaces of such planets a Jupiter and Satum and also the Moon are themselves indications of the effects of such continous bombardments which are 4000000000 years old. So far more than seventy depressions on the Earth's surface have been determined to have formed as a result of the falling of meteorites . These phenomena are becoming extinct because of erosion.One of the most conspicous depressions known is called Barringer which is located in the state of Arizona in the United States , and was created 350000 years ago . Right now the Earth's atmosphere acts as a barrier to such events,in such a way that almost all meteorites burn ,destroy and lose most of their mass while going through it.
It is worth mentioning that an ocean of air, called atmosphere , surrounds the Earth ,and that all living creatures stay at the bottom of this ocean . The Earth's atmosphere is made up of different gases such as nitrogen ( 78.08 % ( , oxygen ) 20.95 % ( ,and argon ( 0.93 % ( . The Earth's present atmosphere has been divided into a few layers . The lowest layer is called Troposphere which is in contact with the Earth's surface , all clouds and the friendly climate for life are located here.This layer extends up to 12 km. The second layer is known as Stratosphere which in some parts extends up to 80 km. This layer contains a thinner layer which is made of a special kind of oxygen called ozone ) O3 (. This thin layer functions as a shield against harmful short wave cosmic radiations such as ultraviolet radiation emitting from the Sun . Without the ozone layer the life on the Earth would definitely face a serious danger . The next layer is named Ionosphere.The X ray and ultraviolet radiations emitted from the Sun are ionized in this layer and transformed into charged atoms and molecules . This layer of the atmosphere plays a distinctive role in establishing radio communications. It is worth mentioning that meteors are small particles of matter in the solar system which when entering the upper layers of the atmosphere are heated by friction , against air particles . Then they glow at about 190 km from the Earth's surface and at 65 km.Or more burn and turn into ashes. Looked from other aspect,complex and long term movements of the Earth which is carried on slowly and solemn not only does not threat life on its surface,but is established in such a way to preserve and stabilize it. It is worth mentioning that the Earth has five types of movement :
1 - rotation,every 24 hours the Earth rotates around its axis at 1667 km/h)in the equator).
2 - revolution, the Earth revolves around the Sun on its somewhat elliptical orbit ) its radius is approximately 149.5 million km. ) once every year at a speed of 30 km/s.
3 - nutation,this movement of the Earth is caused by the change in the direction of the axis of rotation and takes 26000 years to complete.
4 - moving along with other planets of the solar system towards Vega star at 19.5 km/s.
5 - moving along with the milky way galaxy at 270 km/s . This circular movement takes 240 million years to complete.