Composition of earth crust

The soil we live upon is mainly composed of the following two components:
  1. Organic material (includes all kinds of nutriciants)
  2. Inorganic material; the various kinds of stone (for example sand, they contain minarals)
The pH-value can be various: stone of the type 'granite' has a bit lower pH-value (is a littlebit acid), where layers of calcium carbonate are more basic, with a higher pH-value.

The upper earth layer, where we find rivers, seas and oceans, mountains and living creatures, has the following composition:

ELEMENTS PERCENTAGES
Oxygen
47
Silicium
28
Aluminium
8
Iron
5
Calcium
3,5
Sodium
3
Potassium
2,5
Magnesium
2
Other elements
1


The very dominating presence of oxygen and Silicium in the sole is due to the various kinds of sand: SiO2 and its derivatives.
Oxygen, Silicium, Aluminium, Iron and Calcium.
The choice to give some extra attention to these elements has to do with the fact of their abundancy; they are the most important elements in the outer earth crust of about 40 km thick. Humans have enormous profit from these elements.
About 20% of the air is Oxygen; it is number 2 after Nitrogen.
In the earth, Oxygen is the champion number one; about half of the substances in the earth is the element Oxygen, mainly in the form of oxydes.
The oxyde that occurs the most is Silicium oxyde, SiO2 (sand). This is used, for example, in glass and in very important applications of chips in computers and many other digital apparatus.
Aluminium, like many other elements, does not occur in pure form, but only in compounds.
Earth contains a high percentage of Al in the form of Bauxite, Aluminium ore, Aluminium oxyde. You must treat that in a proces of electrolysis to get the pure Aluminium (see module 10). It is a very strong en light metal.
Iron is known for a very long time and found in iron ore (Iron oxyde of course). They obtain the pure Iron in high furnaces with help of Coal.
Calcium is found in stony places, in particular in the form of calcium carbonate.