A story of pebbles
Formed about 4600 million years ago, the Earth is one of the 8 planets in our solar system, including Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, to revolve around the Sun. Its history is revealed by geology, which literally means "speech about the Earth". Geologists search for rocks to discover in them the testimonies of the origins of the Earth and its formation. They study the structures of the Earth’s crust and their evolution.
The structure of the Earth The globe is structured in three parts: the core, the mantle and the crust. The crust and the solid part of the upper mantle form plates that move slowly over the inner mantle, of a more viscous consistency. As we get closer to the center of the Earth, temperatures and pressures rise.
- A : Crust: 6 to 70km thick
- B : The mantle, solid: about 2900km thick
- C : External core, viscous fusion: about 2300km thick
- D : Internal core, very dense: 1200km radius
Tectonics
Tectonics is the science of the structure of the Earth. Along the contact line between two plates (of the crust and the upper part of the mantle of the Earth), are formed mountain ranges, the Himalayas for example.
At the bottom of the oceans, rocks from the mantle rise between the plates and produce oceanic wrinkles.
The meeting of physics, with chemistry and some geometry
The assembly or combination of one or more minerals gives the rocks. Some, such as quartzites (solid quartz) and marbles (calcite), are formed from a single mineral variety. Minerals are defined as inorganic natural solid bodies having a chemical composition of their own and a strictly ordered arrangement of atoms. Here are two known rocks, granite and basalt, with their main minerals:
Granite
A rock always contains different minerals whose size and texture vary according to its mode of formation. For granite, magmatic rock with coarse grains, the three most abundant minerals are visible to the naked eye. These are quartz (grey parts), feldspar (pink and white parts), mica (black parts).
Basalt
Basalt consists of three main minerals: olivine, pyroxene and plagioclase feldspar. However, due to its fine granular construction, it is not always possible to distinguish them with the naked eye.
