Earth Layers and Crust Composition

Earth consists of several concentric layers: crust, mantle, and core, similar to an onion.
The crust is the uppermost layer and is the thinnest, averaging 35 km thick on continental mass and 5 km on ocean floors.
Continental crust, known as sial (silica + alumina), is primarily composed of silica and alumina.
Oceanic crust, referred to as sima (silica + magnesium), consists chiefly of silica and magnesium.
Below the crust lies the mantle, extending up to 2900 km in depth.
The core, the innermost layer, has a radius of approximately 3500 km and is mainly composed of nickel and iron (nife).

The earth's crust is made of various types of rocks, which are natural masses of mineral matter.
Three major rock types exist:
- Igneous rocks are formed from cooled molten magma (primary rocks).
  - Intrusive igneous rocks cool slowly within the earth, forming large grains (e.g., granite).
  - Extrusive igneous rocks form rapidly on the surface from lava, resulting in a fine-grained structure (e.g., basalt).
- Sedimentary rocks are formed from compressed sediments transported by wind and water (e.g., sandstone), often containing fossils.
- Metamorphic rocks arise from igneous or sedimentary rocks subjected to heat and pressure (e.g., clay to slate, limestone to marble).

The rock cycle describes the transformation of one rock type into another.
Igneous rocks can break down into sediments, which then form sedimentary rocks.
When igneous and sedimentary rocks are subjected to high heat and pressure, metamorphic rocks form.
Metamorphic rocks under sufficient heat and pressure can melt into molten magma, which can again solidify into igneous rocks.

Minerals are naturally occurring substances with specific physical properties and chemical compositions.
Important for humanity: fuels (coal, natural gas, petroleum), industrial materials (iron, aluminum, gold, uranium), and medicinal uses (certain minerals and compounds).
Minerals are crucial in agriculture, particularly in fertilizers.