The Earth.

The Earth Diameter 12 756 km Mass 5,98*10^24 kg Density 5510 kg/m^3 The period of rotation 23 h 56 min 4,1sec The average distance from the Sun 1 a.i. (149,6 mln km) The period of revolution 365,26 days Excentricity of the orbit 0,017

The Earth is the third from the Sun big planet in the solar system. Due to its exceptional, perhaps the single in the Universe position to its natural conditions the Earth became the place where the organic life appeared and was developed.

The form and dimensions of the Earth.

By its form the Earth is near to the ellipsoid, flattened at the poles and stretched in the equatorial zone. The middle raiding of the Earth is 6371,032 km, the pole 6356,777 km equatorial - 6378,160 km.

The Earth surface area is 510,2 mln km^2, 70,8% of which is the World ocean. Its middle depth is about 3,8 km, the maximum depth (Marianskaya hollow in the Pacific ocean) is 11,022 km, the water volume is 1370 mln km^3 the middle saltiness 35 g/l. The land is 29,2% and formed the six continents and islands. The greatest height above the sea is (Chomolungma in the Himalayas) 8848 m. The mountains take 1/3 of the land. The middle height of the land above the sea is 875 m. The deserts take about 20% of the land surface, the thin forests - about 20% glaciers - more then 10%. More then 10% of the land are agricultural fields.

According to the modern cosmogonical views the Earth was formed 4,6 - 4,7 billions years ago from the protoplanet cloud captured by the Sun. About 3,5 billions year ago there appeared conditions favourable for the organic life origin. Homo sapiens (a human being) appeared about half a million years ago, and the formation of the modern type of a human being was at the time of the first receding of the glacier i.e. about 40 thousand years ago.

The Earth has the only satellite the Moon (see picture of the Earth from the Moon’s surface). Its orbit is near to the circumference with the radius about 384400 km.

The internal structure.

The main methods in the Earth internal structure investigation are the seismic ones. They are based on the learning: the elastic waves spreading (longitudinal and transverse) which occurred during seismic events (eqarthquakes). The Earth is conditionally divided into 3 parts: a bark a cloak and a core (in the centre). The external layer - the bark is 35 km thick. The main types of the bark are continental and ocean. The thickness of the bark is variable.

The surface deposit thickness is about 2 km. Then comes the granite layer its thickness is about 20 km - 14 km, then there is a basaltic layer. The middle densities are 2,6 g/ sm^ 3 at the Earth surface; 2,67 g/ sm^ 3 at the basalt.

The depth of the cloak is from 35 to 2885 km is also called the silicate shell. It is separated from the bark by the border, called the border of Mofo. Another terrestrial border is so-called Jutenburg’s border that is between the cloak and the external core.

Among the multiple chemical elements of the Earth composition are also radioactive. Their disintegration is as well as the gravitational differentiation (the moving of the solid substances and less solid substances from the central to the far regions). The external core consists of 12% of sulphur and 88% of iron. The temperature of the central part of the Earth is nearly 5000°C. The maximum temperature on the surface is about 60°C (in tropical Africa, and America) the minimum temperature comes to - 90°C (in the central parts of Antarctica).

The pressure is slowly increasing from 0 to 3,61Gp. The heat is transformed to the surface by the processes of thermal conductivity and convection.

The density in the centre of the Earth is about 12,5 g/ sm^3.

Above the Earth.

The Earth is surrounded by the atmosphere (see item ”The Earth atmosphere”). The low layer - troposphere is 14 km in height. In forms the weather on the planet. The next layer is stratosphere with 14 -50-55 km of thickness. More above there is mesosphere (about 80-85 km) with the observed silver clouds. For the biological processes in the Earth the ozone - sphere is very important, it is situated in the height of 12 - 50 km. The region above 50 - 80 km is called ionosphere. At last at the height more then 1000 km the gas is deeply rarefied and at the height of 1,6 and 3,7 of the Earth’s radius there are the first and the second radiation zone of the Earth.

The Earth has a gravitational field. It is perfectly described in the gravity low of Newton (see the gravity law).

The electric field above the Earth surface has the intensity about 100 w/m it’s so-called “ the field of the clear weather”, it is directed vertically down.

Geophysics of our Earth is very young. All the events inside the Earth are not investigated yet perfectly.