11th Class

  Structure and Physiography   Do you know that our earth also has a history. The earth and its landforms that we see today have evolved over a very long time. Current estimation shows that the earth is approximately 460 million years old. Over these long years, it has undergone many changes brought about primarily by the endogenic and exogenic forces. These forces have played a significant role in giving shape to various surface and subsurface features of the earth. You have already studied about the Plate Tectonics and the movement of the Earth's plates in the book Fundamentals of Physical Geography (NCERT, 2006). Do you know that the Indian plate was to the south of the equator millions of years ago? Do you also know that it was much larger in size and the Australian plate was more...

  Drainage System   You have observed water flowing through the rivers, nalas and even channels during rainy season which drain the excess water. Had these channels not been there, large-scale flooding would have occurred. Wherever channels are ill-defined or choked, flooding is a common phenomenon.   The flow of water through well-defined channels is known as 'drainage' and the network of such channels is called a 'drainage system'. The drainage pattern of an area is the outcome of the geological time period, nature and structure of rocks, topography, slope, amount of water flowing and the periodicity of the flow.   Do you have a river near your village or city?   Have you ever been there for boating or bathing?   Is it perennial (always with water) or ephemeral (water during rainy season, and dry, otherwise)? Do more...

  Climate   We drink more water during summers. Your uniform during the summer is different from the winters. Why do you wear lighter clothes during summers and heavy woollen clothes during winters in north India? In southern India, woollen clothes are not required. In northeastern states, winters are mild except in the hills. There are variations in weather conditions during different seasons.   These changes occur due to the changes in the elements of weather (temperature, pressure, wind direction and velocity, humidity and precipitation, etc.).   Weather is the momentary state of the atmosphere while climate refers to the average of the weather conditions over a longer period of time. Weather changes quickly, may be within a day or week but climate changes imperceptivity and may be noted after 50 years or even more.   You have more...

  Natural Vegetation   Have you ever been to a forest for a picnic? You might have surely gone to a park if you live in a city or to a mango, guava or coconut orchard, if you live in a village. How do you differentiate between the natural vegetation and the planted vegetation? The same variety may be found growing wild in the forest under natural conditions and the same tree may be the planted one in your garden under human supervision.   Natural vegetation refers to a plant community that has been left undisturbed over a long time, so as to allow its individual species to adjust themselves to climate and soil conditions as fully as possible. India is a land of great variety of natural vegetation. Himalayan heights are marked with temperate vegetation; the Western more...

  Soils   Have you ever thought about the most important factor which supports trees, grasses, crops and numerous life- forms over the earth's surface? Can one grow a blade of grass without soil? While some plants and organisms which are aquatic in nature can sustain in water, do they not derive nutrients from soil through water? You will realise that soil is the most important layer of the earth's crust. It is a valuable resource. The bulk of our food and much of our clothing is derived from land-based crops that grow in the soil. The soil on which we depend so much for our day-to-day needs has evolved over thousands of years. The various agents of weathering and gradation have acted upon the parent rock material to produce a thin layer of soil.   Soil is the mixture of rock more...

  Natural Hazards and Disasters   You might have read about tsunami or seen the images of horror on television set immediately after it happened. You may also be aware of the severe earthquake in Kashmir on both sides of the Line of Control (LOC). The damage caused to human life and properties during these episodes has moved us all. What are these as phenomena and how they are caused? How can we save orselves? These are some questions which come to our minds. This chapter will attempt to analyses some of these questions.   Change is the law of nature. It is a continuous process that goes on uninterruptedly involving phenomena, big and small, material and non- material that make our physical and socio- cultural environment. It is a process present everywhere with variations in terms of more...

  Geography as a Discipline   You have studied geography as one of the components of your social studies course upto the secondary stage. You are already aware of some of the phenomena of geographical nature in the world and its different parts. Now, you will study 'Geography' as an independent subject and leam about the physical environment of the earth, human activities and their interactive relationships. Therefore, a pertinent question you can ask at this stage is - Why should we study geography? We live on the surface of the earth. Our lives are affected by our surroundings in many ways. We depend on the resources to sustain ourselves in the surrounding areas. Primitive societies subsisted on 'natural means of subsistence', i.e. edible plants and animals. With the passage of time, we developed technologies and started producing our food using natural resources such more...

  The Origin and Evolution of the Earth   Do you remember the nursery rhyme "...Twinkle, Twinkle little star..."? Starry nights have always attracted us since the childhood. You may also have thought of these stars and had numerous questions in your mind. Questions such as how many stars are there in the sky? How did they come into existence? Can one reach the end of the sky? May be many more such questions are still there in your mind. In this chapter, you will leam how these "twinkling little stars" were formed. With that you will eventually also read the story of origin and evolution of the earth.   ORIGIN OF THE EARTH   Early Theories A large number of hypotheses were put forth by different philosophers and scientists regarding the origin of the earth. One of more...

  Interior of the Earth   What do you imagine about the nature the earth? Do you imagine it to be solid ball like cricket ball or a hollow ball with a thick cover of rocks i.e. lithosphere? Have you ever seen photographs or images of a volcanic eruption on the television screen? Can you recollect the emergence of hot molten lava, dust, smoke, fire and magma flowing out of the volcanic crater?   The interior of the earth can be understood only by indirect evidences as neither any one has nor anyone can reach the interior of the earth.   The configuration of the surface of the earth is largely a product of the processes operating in the interior of the earth. Exogamic as well as endogenic processes are constantly shaping the landscape. A proper understanding of more...

  Distribution of Oceans and Continents   In the previous chapter, you have studied the interior of the earth. You are already familiar with the world map. You know that continents cover 29 per cent of the surface of the earth and the remainder is under oceanic waters. The positions of the continents and the ocean bodies, as we see them in the map, have not been the same in the past. Moreover, it is now a well-accepted fact that oceans and continents will not continue to enjoy their present positions in times to come. If this is so, the question arises what were their positions in the past? Why and how do they change their positions? Even if it is true that the continents and oceans have changed and are changing their positions, you may wonder as to how more...