Fundamentals of Soil Science (1+1)

Introduction

Earth's Spheres:

• Three spheres, corresponding to the three states of matter (solid, liquid and gas) constitute the earth. The solid zone is lithosphere, land which is covered by water forming seas and oceans is the hydrosphere, the gaseous envelope over the earth’s surface is the atmosphere.
• The lithosphere consists of continents, oceans basins, plains, plateau and mountains, valleys, sand dunes and also it include interior of earth which consists of rocks and minerals. It is covered by gaseous and watery envelops. It accounts to 93.06 % of the earth.
• The earth ball consists of three concentric rings: crust, mantle and core (Fig-1).
• The crust is 5-56 km thick and consists of rocks with density of 2.6-3.0. It varies from 5 to 11 km in the oceans and 35 to 56 km in the continents. The soil scientists are interested in this skin.

Composition of earth’s crust:

• The hard, naturally formed substance of the earth is referred to as rocks. Rocks are built from minerals.
• Minerals in turn are constructed from natural elements and compounds. Out of total elements known eight element covering major portion 98.6 % ( by weight) of the earth’s crust (up to 16 km).The two elements occurring in greatest abundance are non-metallic ( oxygen and silicon) and comprised of 3/4th (74.32%) of the total composition of the earth crust (Table.1).

Table 1.Eight Major Elements of the Earth’s Crust

Elements		Approx. Abundance (by weight)	Example of mineral
Non-metallic	Oxygen	46.60	Quartz
	Silicon	27.72	Mica
Metallic	Aluminum	8.13	Mica
	Iron	5.00	Pryoxines
	Calcium	3.63	Mica
	Sodium	2.83	Feldspar
	Potassium	2.59	Mica
	Magnesium	2.09	Pryoxines
Others		1.41