The earth has four realms – lithosphere, hydrosphere, atmosphere and biosphere. The lithosphere, the uppermost layer, is made of solid rocks and unconsolidated materials; its literal meaning is 'the sphere of rock'. This chapter covers the three types of rocks, the rock cycle, and the formation, composition, layers, types and conservation of soil.
1. Rocks and Minerals
- Petrology is the branch of geology that deals with the study of rocks – from the Greek 'Petrus' (rock) and 'Logos' (study).
- A rock is an aggregate of one or more minerals. The earth's crust is composed of rocks; they may be hard or soft.
- There are about 2,000 types of minerals on the earth's surface, of which only 8 basic minerals are commonly found all over the earth.
- Minerals are chemical substances that exist in nature as elements or compounds.
By mode of formation, rocks are of three types: Igneous, Sedimentary and Metamorphic.