The geosphere
If we remember the dimensions of terrestrial radio, just over 6.300km in Ecuador A simple calculation (about the shape of the spherical planet) leads us to know its volume: the more accepted figure is expressed in the notation x1010km3 scientific about 1.08.
The land mass, ie the amount of matter that the form was estimated at almost 5.9 x 1021 tons. A simple conclusion was to recognize the density of the planet: more than 5.5 g/cm3.
But the experimental confirmation of the density of rocks on the earth's crust near 2.5g/cm3. The explanation of the difference between a fact and the other was simple: inside the planet should be higher density. Four more information
allowed progress in the assessment of the internal structure of the earth: a) findings about earthquakes and tsunamis; b) the study of volcanic activity and the rocks were formed from the lava ejected in eruptions; c) the use of special waves emitted by the planet; d) exploring the ocean floor.
Already in 1760, had proposed that earthquakes were caused by the vibrations caused by the layers accommodations located below the crust. The invention of the seismograph in 1855 (a simple device which allowed to measure these waves and know in advance the event of earthquakes) and was expanded information to confirm the above hypothesis. It also allowed to organize the evacuation of some areas before the occurrence of the phenomenon.
Research volcanic activity allowed us to establish a match in the major seismic zones: there is a real circle of volcanoes and earthquakes around the Pacific. An area of \u200b\u200binstability and escape of molten rock can mean the existence of semi-solid materials and high land surface temperatures.
Since the late nineteenth century with the construction of underwater cameras, sought to unravel the mysteries of the deep sea. The names of A. Piccard, J. Cousteau were attached to underwater exploration. The greatest achievements came from bathyscaphe, cousteau name that he gave his submarine, especially able to withstand high pressure during the descent to the ocean trenches. So we noted the presence of living organisms to more than 10km in depth and the existence of a similar undersea emerged, with plateaus, ridges and mountains (which have become islands, sometimes very distant from the continent)
The discovery of the Atlantic ocean ridge, a vast underwater fault continually brings materials from deep mantle to form new seafloor in the Atlantic Ocean, allowed the understanding of seafloor spreading, but this accumulation of new materials increases the planet's surface because this effect is offset by the phenomenon of subduction, which consists of the introduction of crustal material in other areas (for example, on the Pacific coast of America) to the upper mantle are mixed and melt rocks to start a new cycle.
The analysis of seismic waves produced by earthquakes or explosions
experimental provide any new information about the internal structure of the planet was found that there was a rocky field homogeneous, but consisted of several concentric layers of nature varied. Were different types of waves, some other surface and deep some fast and another slow, depending on the type of material that passed through. This could make the primary waves (P waves) from secondary (S waves), the former is transmitted through any medium (solid or liquid). S waves, however, do not through liquids. In addition, it was found that P waves are transmitted more rapidly than through denser materials. 
Below 32 to 40km, it was recognized a change in velocity of the seismic zones and, therefore, significant variation of the density of the material underground. Another significant change was identified approximately to 1.5000km deep. The loss of S-wave transmission was localized to a depth of 2.900km. With these data, geologists determined the existence of several layers at different depths.
According to the above, on the planet are distinguished basically the following layer: cortex (less than 500 º C) up to 40km, the mantle (where there is a notable increase pressure and temperature) which extends to 1,500 km depth; the outer core, to 2,900 km (close to 2,500 ° C) and the inner core on which state aggregation remain different theories, which, however, agree at high temperatures (about 5,000 º C) of incredible pressures (more than 30.000toneladas/cm2), and the presence of typical metal by its density and magnetic properties as nickel and iron.
However, in the earth's surface the most abundant compounds are the combinations of oxygen with silicon and aluminum, while greater depths are recognized silicon and magnesium oxides.
Arranged in horizontal layers, regardless of Earth's spherical shape, materials and features can be summarized as follows:
The rocks found on the surface are actually the only piece of evidence of what exists inside the earth and the transformations undergone by these materials, but only the first kilometers of the mantle.
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