 As we all know that the earth is the only planet where we have life. So this planet is a part of a system which is called a solar system. In our solar system, this planet is or some are called the word, is the only planet where we can find a life over it. So this life actually is present in the form of human life, the plant life, animal life and marine life. So this actually planet has a sustainable environment. So that's why this sustainability creates the life over it. So if we see this planet from the moon, we saw it in different colors like its blue color is because of water. That is only because of the forest or the vegetal cover. And the white color shows the area which is under the ice. So this planet or earth was formed around 4.6 billion years ago. The earth passes through different phases of development. Some eras were under volcanism and some were under drought. So we can say that when this planet was formed, then the state of it was in the gaseous state and the liquid state. We still get the benefits of this in the interior of the earth. But the upper crystal part, which is called earth crust, it has cooled down along with the passage of time. And now we see that we get continents there and different areas which are under grassland, the areas which are under ice cover. So these are the actually different phenomena which are over the earth surface. Biodiversity has evolved over hundreds of millions of years. It is currently home to 10 to 14 million species of life including over 7.5 billion humans. All depend on the biosphere and natural resources. So when we talk about different species, we see different species because of different areas. The differences of the climate, differences of the varieties of the surface, some areas are under ice summer, some are under vegetal cover, some are under island type of climate, some are under the mountain type of climate. So these are the variety of the surfaces. So that's why we have variety of the lives over it. So these lives are under certain environment which is called habitats. Like if we take an example of desert, then the vegetal cover will be different. The way you can see it in this slide, this is actually the desert environment. Some are actually under the tropical rainforest. So here you will find thick forest. Here life will be in extensive form. The vegetal cover will be dense. But the population will be less. But the moderate areas which are under savannah, the wetlands or some are the areas which are under form type of climates. So as we call agriculture land, the residential areas or settlements will be seen there. And these settlements can be urban or rural as well. But the developed areas and the settlements will be dispersed by the rural type of environment. Whereas if these settlements are in rural developing areas, then there will be a nucleated form. Because the number of persons there will be more than 5 kms. But the urban areas are mostly in the developed world. So why because of the opportunities? Why because of the information flow? So these actually the things which are related to different opportunities or resources. Now the sun is the only source of energy which provides energy in the form of heat and light. The earth is surrounded by the atmosphere, a layer of some important gases, important for the survival of the life. We have a very beautiful example of the solar system where the sun is the main star which gives us energy in the form of light and heat. That means we get light from it, we also get energy from it. And all this transmission of energy is in short wave radiation. That means all this radiation is reaching us in short wave. But through atmosphere, atmosphere is actually like an envelope which is surrounded by the earth, the planet. So what we get from the atmosphere is the earth's earth grid and a protected shield. From here when the short wave passes it heats up the earth's surface. Earth's surface which is called earth crust and after this heat up long wave radiation emission starts from here. And this long wave radiation heats up the atmosphere. That means the long wave is the atmospheric gases, the permanent gases or the variable gases absorb the gases in the long wave radiation. And from this we get counter radiation from which we feel the air temperature which is called sensible heat flow. So all are actually under a system. So this we have to keep in mind that the earth is because we have such an atmosphere that is present there and that is why life is seen there. So the earth human population is divided among about 200 sovereign countries. So these are actually the countries of the world. Every country has its own boundary. So that's why the certain areas are under certain government. So some areas are under the like the southern part of Asia. You can see that the number of countries are divided into certain boundaries. Like South Asia, you have the eight countries in which Afghanistan, Pakistan, India, Bangladesh, Sri Lanka, Maldives, Bhutan and Sri Lanka.