Class 07 Geography NCERT

Environment is a combination of natural and human made phenomena. While the natural environment refers to both biotic and abiotic conditions existing on the earth, human environment reveals the activities, creations and interactions among human beings.

The earth is made up of several concentric layers with one inside another. The uppermost layer over the earth’s surface is called the crust. The main mineral constituents of the continental mass are silica and alumina. The oceanic crust mainly consists of silica and magnesium.

The lithosphere is broken into a number of plates known as the Lithospheric plates. The movement of these plates causes changes on the surface of the earth. The forces which act in the interior of the earth are called as Endogenic forces and the forces that work on the surface of the earth are called as Exogenic forces.

The earth is surrounded by a huge blanket of air called atmosphere. Nitrogen and oxygen are two gases which make up the bulk of the atmosphere. Carbon dioxide, helium,
ozone, argon and hydrogen are found in lesser quantities.

The sun’s heat causes evaporation of water into vapour. When the water vapour cools down, it condenses and forms clouds. From there it may fall on the land or sea in the form of rain, snow or sleet.

The tropical region lies very close to the equator; between 10°N and 10°S. So, it is referred to as the equatorial region. The river Amazon flows through this region. It flows from the mountains to the west and reaches the Atlantic Ocean to the east. Numerous tributaries join the Amazon River to form the Amazon basin.

Desert is an arid region characteriesed by extremely high or low temperatures and has scarce vegetation. Depending on the temperatures there can be hot deserts or cold deserts.