The earth is sphere in shape and its visible features can be experienced on the surface. But, huge size of earth, increasing temperature and pressure limited the direct observations. The earth has three concentric layers NIFE, SIMA and SIAL.
These three layers have difference over temperature, pressure and density. The uppermost layer has most significant part called Crust containing rocks. On the basis of formation rocks are of three types - Igneous, Sedimentary and Metamorphic.
With the span of time, these rocks are also disintegrated physically or chemically. This process is termed as weathering and changes the face of earth's surface.
Structure of the Earth's Interior
The interior part of the earth cannot be observed directly due to increasing temperature and pressure and also restrict deep drilling. On the basis of limited direct observation and other sources, earth’s interior has been divided into three concentric layers.
Core (NIFE): 3500 km
- Inner Solid Layer
- Outer Semi Liquid layer
Mantle (SIMA): 2800 km
Lithosphere (SIAL): 100 km
Crust: 8 - 40 km
Temperature, Pressure and Density
Temperature increases with increase in depth but increase is not uniform. The pressure of overlaying rock increases with depth. Pressure at core is more than 3-4 more million times than at sea level. The increasing temperature and pressure resulted in increasing density towards core.
Types of Rocks
Igneous Rock
The word igneous is derived from the Latin word 'ignis' meaning fire. It is Made from cooling of magma. It is formed at different depths not exceeding 40 km. When magma is ejected to the surface, it is called lava.
As they comprise the earth's first crust these are called the parent of all rocks or the primary rocks.
Types of Igneous Rocks:
- Extrusive igneous rocks - formed by cooling of lava on the earth’s surface. Example: Gabro, Besalt
- Intrusive igneous rocks - formed below the earth's surface. Example: Granite and dolerite
Sedimentary Rocks
Formed due to continuous deposition of sediments received from existing rocks. These sediments are layered or stratified. These rocks have fossils in their layers.
The broken rock particles are transported by running water, ocean currents, glaciers or even by wind from one place to another. These broken material are soft and unconsolidated in beginning and later hardened to a compact material by excessive pressure and cementation to form sedimentary rocks.
Folded Mountains like Himalaya and Alps are made of sedimentary rocks.
Metamorphic Rocks
Metamorphic rocks are formed under the influence of heat or pressure on sedimentary or igneous rocks. Tremendous pressure and high temperature change the colour, hardness, structure and composition of all types of pre-existing rocks. The process of this change is called Metamorphism.