Grade -8 (Science) : Structure of Earth

 

              Unit :-19   Structure of Earth

Mineral :The pure substance which occurs naturally are called mineral .There are two types of minerals :

1.)Metallic mineral :The mineral from which metals can be obtained or extracted are called metallic mineral .

Ores minerals :The metallic minerals from which metals can be obtained economically are called ores minerals .For example :

S.N.	Metals	Ore mineral(Ores)
1. 2 3. 4.	Iron Aluminium Copper Silver	Haematite, Magnetite Bauxite , Feldspar Chalcopyrite ,Chalcocite Argentite, Horn silver

2.)Non-metallic minerals :The minerals which do not contain any metals or contains a very less fractions of metals are called non-metallic minerals .There are 2 types of non- metallic minerals :

i)Gem minerals    ii)Non gem minerals

Characteristics of minerals :

i)They are pure substance so they their own molecular formula .

ii)They are natural substance.

iii)They are crystalline .

iv)They may be transparent or opaque .

Uses of minerals :

I)Some precious metals i.e.gold ,silver etc. are used as ornaments .

ii)They are used as source of metals .

iii)Some minerals are used as raw materials for different industries .

Minerals found in Nepal :

i)Iron :Fulchoki,

ii)copper :Makwanpur , Dhading.

iii)Lead :Fulchoki, Solukhumbu .

iv)Zinc :Fulchoki ,Makwanpur .

v)Graphaite :Ilam, Dhankuta

Soil: The weathered rock as it is formed the particles of rock like clay,slit and sand is called soil .

Ways of the Formation of soil :

i)River water transport stone when they strike each other small particles of rocks are formed that covert into soil.

ii)Due during day hot and night cold on rocks causes of weathering .The weathered particles form soil.

iii)The speedy wind remove the weathered rocks particles which takes part in the formation of soil.

iv)Roots of plants increase the distance between cracks of rocks which causes of erosion that lead to formation of soil.

Soil profile :The vertical section soil exposing a set of horizon from the upper surface of soil to the bed rock is called soil profile .

 Humus: The organic component of soil ,formed by the decomposition of leaves and other plants materials by soil micro –organism  is called humus. It help to the hols water and minerals

Weathering :Weakening rocks and minerals is called weathering .The physicals methods of weathering are as following are as following :

i)By speed of water cracks the rocks .

ii)By change in temperature  on rocks at day and night .

iii)By roots of plants which pass in the hard rocks .

iv)By burrowing animals which expose the rocks for erosion.

Soil erosion :The removal of weathered particles from a rocks is called soil erosion .

Deposition :The collection of eroded particles is called deposition .After erosion the eroded particles are collected at another place so, erosion and deposition occurs side by side 

Effects of soil erosion :

i)By soil erosion soil loss their fertility and make the land barren .

ii)Soil erosion leads to desertification (i.e. increase desert area)

Conservation of soil .Soil is a very important natural resources .It `provides habitat for plant and animals .Therefore we should conserve the soil .

Ways of soil conservation

i)Deforestation should be controlled .

ii)Traces forming should be done on slopes of hilly region .

iii)Afforestation should be done on open and bare field .

iv)Uncontrolled overgrazing should be controlled .

v)Plats having strong roots i.e. bamboo ,should be planted on the bank of river .

vi)Embankment  should be done in riverside .