In meteorology, the term cyclone can be defined as the rapid inward circulation of air masses about a low-pressure centre which is circling counter-clockwise in the northern hemisphere and clockwise in the southern.

Types of Cyclone

1. Tropical Cyclone: It occurs over tropical ocean regions. it is two types- Hurricanes and typhoons. Hurricanes are found in the Atlantic and Northeast Pacific, whereas typhoons are found in the Northwest Pacific. On the basis of intensity and wind speed, this cyclone is classified into five categories- 1, 2, 3, 4 or 5. Category 5 has a wind speed of 155 mph or above.

2. Polar Cyclone: It occurs over Polar Regions of Greenland, Siberia and Antarctica. It is strong during the winter season.

3. Mesocyclone: It is a vortex of air within a convective storm. It is the air that rises and rotates around a vertical axis, usually in the same direction as low-pressure systems in a given hemisphere. These types of cyclones are accompanied by the rotating air within the thunderstorm.

Since geography is relates to studying the Earth, and the Earth is continually changing. Nothing on Earth remains in a static position. The only constant on the Earth is change. The rate of things change differs from place to place.

The geographical phenomena, both human and physical, are highly dynamic. They change gradually because of the inter-active processes between ever hanging earth and ever-active and untiring human beings. There subsist changes over the earth’s surface in its physical as well as human and cultural environs.

Many phenomena are similar and several are dissimilar. It is, thus, logical to distinguish geography as the study of a real differentiation. Therefore, geography is supposed to study those phenomena that differ over space. Geographers study the changes/variations/adaptations in the phenomena over the surface of the earth as well as study the relations with the other factors that cause these changes.

For instance, cropping patterns vary from area to area; however this variation in cropping pattern, as a phenomenon, is associated with changes in climates, soils, market demands, and ability of a farmer to invest and technological inputs available to them. Therefore, the concern of geography is to discover the causal connection between any 2 phenomena or between more than one phenomena.

Primitive human societies were directly reliant on their immediate environs. Geography, therefore, is connected with the study of Human and Nature inter-actions as a unified whole. ‘Human is an essential part of ‘nature’ and ‘nature’ has the human imprints. ‘Nature’ has impacted different facets of human life. Its imprints is seen on clothing, food, occupation, and shelter. Human beings have gradually accepted nature by way of adaptation and modification.

Drainage pattern is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. They are governed by the topography of the land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land. A dendritic drainage pattern is the most common form and looks like the branching pattern of tree roots. It develops in regions underlain by homogeneous material. That is, the subsurface geology has a similar resistance to weathering so there is no apparent control over the direction the tributaries take.

The Ganga is the most important river of India both from the point of view of its basin and cultural significance. It rises in the Gangotri glacier near Gaumukh which is 3,900 m high from sea level in the Uttarkashi district of Uttarakhand. It is known as the Bhagirathi in this region

• The earth is predominantly (71 % of the earth's surface) covered with water. Water absorbs the white light in the radiation (sunlight). The sunlight through appears white it is actually a combination of lights of several different colors (Violet, indigo, blue, green, yellow, orange and red). 
• When sunlight reaches the water; the water absorbs, lights of all colors in the white light and reflects only blue light. Thus, the earth from space appears blue. If the water absorbs all colors and reflects only yellow, then it would appear yellow.

There were lots of hypothesis regarding the origin of life on earth. Certain experts suggested that life came from outer space as spores while another group explained that life came from a non-cellular component such as decaying matters like mud. The latter theory was known as the theory of spontaneous generation, which was discarded later.

In the year 1953, Oparin and Haldane suggested that life originated from non-living organic molecules like proteins and RNA. This was followed by the theory of chemical evolution which suggested that atmospheric conditions of earth led to the formation of organic molecules from inorganic molecules. Few scientists conducted experiments regarding the same. However, once the first life came into existence, they started to evolve in different ways and forms. This laid a stepping stone to the theory of evolution.