NCERT Notes and Solutions for Class 7
Inside the Earth
The earth is the only planet in the solar system in which life exists.
Interior of the Earth:
The earth has serval layers, one inside another.
The uppermost layer of the earth’s surface is called Crust. It forms only 1% of the volume of earth.
- Continental masses: * Thickness (35 km)
* Main minerals are: Silica (Si), Alumina (Al)
- Oceanic crust: * Thickness (5 km)
* Main minerals are: Silica (Si), Magnesium (ma)
Mantle: Mantle is the layer of earth surface which is below cust. Depth of mantle is 2900km. It consists of 84% of the earth.
Core: Core is the innermost layer having a radius of about 3500 km. It is mainly made up of Nickle (ni) and Iron (Fe). It has a high temperature and pressure. 15% of the earth’s surface is made up of core.
Point to Remember:
The deepest mine in the world is in South Africa which is 4km deep.
The radius of the earth is 6371 km.
Rocks and Minerals:
- Rocks are made up of substances which are mostly found in solid sates are called minerals.
- Rocks have the following classifications-
(A) Igneous rocks- It is formed when molten magma solidified.
Example: Mica, Basalt, Granite etc.
(B) Sedimentary rocks – Under high pressure, rock particles and organic matters from layers, which in turn form sedimentary rocks.
Weathering is a process of changing of heavy rocks into fragments.
(C) Metamorphic rocks – Under high pressure, heat and action of wind or water igneous or sedimentary rocks converted to metamorphic rocks.
Rock cycle:It is a process of transformation of rocks from one form to another.