Soil is the uppermost layer of the earth’s crust. It contains a mixture of fine powdered rock material and humus. Humus is the organic matter which is added to the soil by the decayed and decomposed remains of plants and animals.
Down to a depth of 16 km from the surface of land, 95 per cent of the earth materials found in the earth’s crust consist of rocks. Rocks are made up of individual substances, called minerals, found mostly in solid state.
Earth’s axis is an imaginary line which runs right across and passes through the centre of the earth. The earth spins round its axis which always remains inclined at an angle of 661/2° to the plane of the Earth’s orbit.
Vegetation comprises of plants growing over the surface of the earth. The plant geographers have divided the vegetation of the world into four great biochores :
The Forest Biochore : Defined as plant formation consisting of trees growing close together nd forming a layer of foliage that shades the ground.
A globe has two fixed points—the North Pole and the South Pole. An imaginary line equator is drawn in such a way that at all points it lies exactly halfway between the two poles. It divides the earth into two equal parts i.e., the Northern Hemisphere and the Southern Hemisphere.
There are three major Landforms : mountains, plateaus and plains. Mountains An uplifted portion of the earth’s surface is called a hill or a mountain. Mountains are classified into the following four types.
The sequence of eating and being eaten and the resultant transfer of energy from one level to another is known as the food chain. The plants and algae are the first level in food chain and are known as primary producers.
Alfred Wegener was the geologist who in 1924 propagated the theory of continental drift which is very much in vogue now. According to this theory, nearly 150 million years ago,there was a single continent on earth known as ‘pangaea’ which broke into several pieces and began to drift apart.