- Geography Introduction: Geography is a field of science devoted to the study of the lands, the features, the inhabitants, and the phenomena of Earth. Geography has been called "the world discipline" and "the bridge between the human and the physical science". Geography is divided into two main branches: human geography and physical geography.
- Earth in Solar Planet:
- The sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar system. We often call it a solar family, with the sun as its Head.
- There are eight planets in our solar system. In order of their distance from the sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
- Till recently (August 2006), Pluto was also considered a planet. However, in a meeting of the International Astronomical Union, a decision was taken that Pluto like other celestial objects (Ceres, 2003 UB313) discovered in recent past may be called ‘dwarf planets.”
- An easy way to memorise the name of the planets in order of their distance from the sun is: MY VERY EFFICIENT MOTHER JUST SERVED US NUTS.
- Geographic Coordinates: Latitude, Longitude, Equator, Tropic of Cancer, Capricorn, Hemispheres, Torrid, Temperate zone.
- Motions of the Earth
- Earth has two types of motions, namely rotation and revolution.
- Rotation is the movement of the earth on its axis. The earth takes about 24 hours to complete one rotation around its axis. The period of rotation is known as the earthday. This is the daily motion of the earth.
- Revolution is the movement of the earth around the sun in a fixed path or orbit. It takes 365 days, 6 hours (one year) to revolve around the sun.
- Six hours saved every year are added to make one day (24 hours) over a span of four years. This surplus day is added to the month of February. Thus every fourth year, February is of 29 days instead of 28 days. Such a year with 366 days is called a leap year.
- The longest day and the shortest night at these places occur on 21st June. At this time in the Southern Hemisphere all these conditions are reversed. It is winter season there. The nights are longer than the days. This position of the earth is called the Summer Solstice.
- On 22nd December, the Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it. As the sun’s rays fall vertically at the Tropic of Capricorn (23½° S), a larger portion of the Southern Hemisphere gets light. Therefore, it is summer in the Southern Hemisphere with longer days and shorter nights. The reverse happens in the Northern Hemisphere. This position of the earth is called the Winter Solstice.
- On 21st March and September 23rd, direct rays of the sun fall on the equator. At this position, neither of the poles is tilted towards the sun; so, the whole earth experiences equal days and equal nights. This is called an equinox.
- Structure of the Earth and its Layers
- Earth - Physical characteristics
- Earth is the third planet from the Sun, the densest planet in the Solar System and the only astronomical object known to harbor life.
- According to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago.
- Mean radius = 6,371.0 km
- Equatorial radius = 6,378.1 km
- Polar radius = 6,356.8 km
- Surface area = 510,072,000 km2
- Mass = 5.97237×10 *24 kg
- Earthquake and Earthquake Waves.
- Maps
- A map is a representation or a drawing of the earth’s surface or a part of it drawn on a flat surface according to a scale. There are three Components of Maps – distance, direction and symbol.
- Physical Maps:
- Maps showing natural features of the earth such as mountains, plateaus, plains, rivers, oceans etc. are called physical or relief maps.
- Political Maps:
- Maps showing cities, towns and villages, and different countries and states of the world with their boundaries are called political maps.
- Thematic Maps:
- Some maps focus on specific information; such as road maps, rainfall maps, maps showing distribution of forests, industries etc. are known as thematic maps. Suitable titles are given on the basis of information provided in these maps.
- Continents
- There are 7 major continents. These are separated by large water bodies. These continents are – Asia, Europe, Africa, North America, South America, Australia and Antarctica.
- Asia is the largest continent. It covers about one third of the total land area of the earth. The continent lies in the Eastern Hemisphere. The Tropic of Cancer passes through this continent. Asia is separated from Europe by the Ural mountains on the west
- Europe is much smaller than Asia. The continent lies to the west of Asia. The Arctic Circle passes through it. It is bound by water bodies on three sides.
- Africa is the second largest continent after Asia. The Equator or 00 latitude runs almost through the middle of the continent. The Sahara Desert, the world’s largest hot desert, is located in Africa. The continent is bound on all sides by oceans and seas.
- North America is the third largest continent of the world. It is linked to South America by a very narrow strip of land called the Isthmus of Panama.
- South America lies mostly in the Southern Hemisphere. The Andes, world’s longest mountain range, runs through its length from north to south.
- Australia is the smallest continent that lies entirely in the Southern Hemisphere. It is surrounded on all sides by the oceans and seas. It is called an island continent.
- Antarctica, completely in the Southern Hemisphere, is a huge continent. As it is located in the South Polar Region, it is permanently covered with thick ice sheets. There are no permanent human settlements. Many countries have research stations in Antarctica. India also has research stations there. These are named as Maitri and Dakshin Gangotri.
- Oceans
- Oceans are the major part of hydrosphere. They are all interconnected. The 5 major oceans are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean and the Arctic Ocean, in order of their size.
- Pacific Ocean is the largest ocean. It is spread over one-third of the earth. Mariana Trench, the deepest part of the earth, lies in the Pacific Ocean. The Pacific Ocean is almost circular in shape. Asia, Australia North and South Americas surround it.
- Atlantic Ocean is the second largest Ocean in the world. It is ‘S’ shaped. It is flanked by the North and South Americas on the western side, and Europe and Africa on the eastern side. The coastline of Atlantic Ocean is highly indented. This irregular and indented coastline provides ideal location for natural harbours and ports. From the point of view of commerce, it is the busiest Ocean.
- Indian Ocean is the only ocean named after a country, that is, India. The shape of ocean is almost triangular. In the north, it is bound by Asia, in the west by Africa and in the east by Australia.
- Southern Ocean encircles the continent of Antarctica and extends northward to 60 degrees south latitude.
- Arctic Ocean is located within the Arctic Circle and surrounds the North Pole. It is connected with the Pacific Ocean by a narrow stretch of shallow water known as Berring strait. It is bound by northern coasts of North America and Eurasia.
- Atmosphere
- The earth is surrounded by a layer of gas called the atmosphere. This thin blanket of air is an integral and important aspect of the planet.
- The atmosphere is divided into five layers based on composition, temperature and other properties. These layers starting from earth’s surface are called the troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere.
- The atmosphere is composed mainly of nitrogen and oxygen, which make up about 99 per cent of clean, dry air.
- Nitrogen 78 per cent, oxygen 21 per cent and other gases like carbondioxide, argon and others comprise 1 per cent by volume.
- Earth's Atmosphere Layers
- Biosphere
- The biosphere is the narrow zone of contact between the land, water and air.
- It is in this zone that life, that is unique to this planet, exists.
- The organisms in the biosphere may broadly be divided into the plant kingdom and the animal kingdom.
- Major Landforms of the Earth
- Mountains is any natural elevation of the earth surface. The mountains may have a small summit and a broad base. It is considerably higher than the surrounding area.
- There are three types of mountains- Fold Mountains, Block Mountains and the Volcanic Mountains.
- The Aravali range in India is one of the oldest fold mountain systems in the world. The range has considerably worn down due to the processes of erosion. The Appalachians in North America and the Ural mountains in Russia have rounded features and low elevation. They are very old fold mountains.
- Block Mountains are created when large areas are broken and displaced vertically. The uplifted blocks are termed as horsts and the lowered blocks are called graben. The Rhine valley and the Vosges mountain in Europe are examples of such mountain systems.
- Volcanic mountains are formed due to volcanic activity. Mt.Kilimanjaro in Africa and Mt.Fujiyama in Japan are examples of such mountains.
- Plateau is an elevated flat land. It is a flat-topped table land standing above the surrounding area. A plateau may have one or more sides with steep slopes. The height of plateaus often varies from few hundred metres to several thousand metres. Plateaus, like mountains may be young or old. The Deccan plateau in India is one of the oldest plateaus.
- Plains are large stretches of flat land. They are, generally, not more than 200 metres above mean sea level. Some plains are extremely level. Others may be slightly rolling and undulating. Most of the plains are formed by rivers and their tributaries.
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