Earth The Planet

Looking outward from the sun, the earth is the third planet of our solar system. Although there is water and atmosphere on other planets, the life is sustainable only on the earth.
The shape of the earth is an imperfect sphere. It is slightly more convex at the equator and slightly flattened at the poles. It is enveloped in a gaseous atmosphere. The earth's body consists of rocks and metals.
The earth's diameter is 12.756 kilometres. It completes the circle around the sun every 365,242 days. The distance it covers during that time is 939.886.400 kilometres, moving at 106.000 kilometres per hour. Its constant companion is the moon. The earth spins on its axis, turning around once every 23 hours, 56 minutes and 4,1 seconds. At the poles, the turn is slower than at the equator. The earth's axis is tilted 23,5 degrees. The tilt is why we have seasons: as the earth travels, different regions face the sun.
The earth is surrounded by a magnetic field, which is linked to the convective flows of the earth's outer core. Their movement creates electrical currents, which transform the earth into a giant magnet. The earth has a magnetic south pole and a magnetic north pole, these, however, are not identical with the geographic poles.
The earth's core consists of two parts. The inner core, which has a 2.400-kilometre diameter, is made up of solid iron and nickel, while the outer core, which has a thickness of 2.300 kilometres, consists of molten iron and nickel. The mantle, with a thickness of 2.800 kilometres, surrounds the core. Its lower level is composed mostly of silicon, iron, and magnesium, while its upper part contains mainly magnesium and ferrous silicates. The region separating the upper mantle from the lower mantle is called asthenosphere. It is approximately 100 kilometres thick.
The mantle is covered by the earth's crust. Together, the earth's crust and the upper mantle form the lithosphere. The lithosphere consists of about a dozen of slowly moving tectonic plates. In the past, this movement created mountain ranges and caused the break-up of the supercontinent, which led to the formation of smaller continents.
On the average, the temperature rises 30 degrees Celsius every 100 metres going from the earth's surface to the core. In the earth's mantle are convective flows, which carry to the earth' surface energy produced by decaying radioactive elements in the earth's interior. They are also the force that moves the plates embedded in our continents.
According to radiometry measurements, the age of the earth is estimated at approximately 4,65 billion years. This estimate is supported by meteorites that have the same geological structure as the earth's core.