Geography
THE EARTH
Nebular Theory There are many ideas about the formation and evolution of the Solar System. The accepted idea is that 4.6 billion years ago, there was a very big cloud of gas in our area of space, known as a nebula. The Nebula eventually became so big that gravity pulled all the gas to the center. Eventually because of all the gas it became so hot there that some hydrogen atoms fused together to make helium. As they did this a lot of energy was let out. All this energy eventually made the Sun.
The leftover gas and dust made the planets, their moons, asteroids and all other objects in the Solar System. Scientists think now that solar systems are created out of a huge cloud of gas. The process by which the solar sytems are created is called the Nebular Theory.
THEORIGINOFEARTH
The formation of Earth occurred as part of the formation of the Solar System. It started as alarge rotating cloud of dust and gas. This cloud, the solar nebula, was composed of hydrogen and helium produced in the Big Bang, as well as heavier elements produced in supernovas. Then, about 4.68×109 years ago, the solar nebula began to contract, rotate and gain angular momentum.
This may have been triggered by a star in the region exploding as a supernova, and sending a shock wave through the solar nebula. As the cloud rotated, it became a flat disc perpendicular to its axis of rotation. Most of themass concentrated in the middle and began to heat up. Meanwhile, the rest of the disc began to break up into rings, with gravity causing matter to condense around dust particles. Small fragments collided to become larger fragments, including one collection about 150 million kilometers from the center: this would become the Earth. THE LAST 2½ BILLION YEARS OR SO As soon as the oxygen was produced by photosynthesis it was taken out again by reacting with other elements (such as iron).This continued until about 2.1 billion years ago when the concentration of oxygen increased markedly. As oxygen levels built up and then . . . . . . The ozone layer was formed which started to filter out harmful ultraviolet rays. This allowed the evolution of new living organisms in the shallow seas.
Earth Solar System Earth solar system consists of : • The Sun • The Planets • Dwarf Planets and countless fragments of left – overs called asteroids, meteors, comets and satellites of the planets (Called small solar system Bodies).
SolarSystemSomeFacts
• Biggest Planet : Jupiter
• Smallest Planet : Mercury
• Nearest Planet to Sun : Mercury
• Farthest Planet from Sun : Neptune
• Nearest Planet to Earth : Venus
• Brightest Planet : Venus
• Brightest star after Sun : Sirius
• Planet with maximum satellites: Jupiter
• Coldest Planet : Neptune
• Hottest Planet : Venus
• Heaviest Planet : Jupiter
• Red Planet : Mars
• Biggest Satellite : Gannymede
• Smallest Satellite : Deimos • Blue Planet: Earth
• Morning/Evening Star: Venus
• Earth's Twin : Venus
• Green Planet : Neptune
• Planet with a big red spot : Jupiter
• Lord of the Heavens : Jupiter
• Greatest Diurnal Temperature: Mercury
Important Parallels of Latitude
1. The Tropic of Cancer :It is in the northern hemisphere at an angular distance of 23 1/2° (23°30‘N) from the equator.
2. The Tropic of Capricorn :It is in the southern hemisphere at an angular distance of 23 1/2° (23°30‘S) from the equator.
3. The Arctic Circle :It lies at a distance of 66 1/2° (66°30‘N) north of the equator.
4. The Antarctic Circle :It lies at a distance of 66 1/2° (66°30‘S) south of the equator. There are two solstices each year, called the Summer Solstice and the Winter Solstice.
Summer Solstice :The day of 21st June when the sun is vertically overhead at the Tropic of Cancer (23°30‘N).
Winter Solstice :The day of 22nd December when the sun is vertically overhead at the Tropic of Capricorn (23°30‘S).
Meridians of Longitude The semi-circles running from pole to pole or from north to south are known as meridians of longitude and distance between them is measured in degrees of longitude. Greenwich Meridian or Prime Meridian with a value of 0° longitude serves as a common base for numbering meridians of longitude lying on either side of it—east as well as west. There are 360 meridians including Prime Meridian. Each degree of a longitude is divided into sixty equal parts, each part is called a minute. Each minute is again divided into sixty equal parts, each part being called a second. Local Time :Local time of any place is 12 noon when the sun is exactly overhead. It will vary from the Greenwich time at the rate of four minutes for each degree of longitude.
Greenwich Mean Time :The time at 0° longitude is called Greenwich Mean Time. It is based on local time of the meridian passing through Greenwich near London. Indian Standard Time :It is fixed on the mean of 82 1/2°E Meridian, a place near Allahabad. It is 5 1/2hours ahead of Greenwich Mean Time. Facts about earth
• The Earthalso called Blue Planet. It is the densest of all planets.
•Earth Circumference: 40,232 Kilometers.
•Earth Area: 510 million Square Kilometers
•Average distance from sun:149 million Kilometers.
•Earth Perihelion:Nearest position of earth to sun. The earth reaches its perihelion on January 3 every year at a distance of about 147 million-Kilometers.
•Aphelion:Farthest position of earth from sun. The earth reaches its aphelion on July 4, when the earth is at a distance of 152 million Kilometers.
• The shape of the earth is oblate spheroid or oblate ellipsoid (i.e. almost spherical, flattened a little at the poles with a slight bulge at the centre). Types of Earth Movements: 1. Rotation or daily movement. 2. Revolution or annual movement. EarthRotation
• Spins on its imaginary axis from west to east in 23 hrs, 56 min and 40.91 sec.
• Rotational velocity at equator is 1667 Kilometers/h and it decreases towards the poles, where it is zero. Earth’s rotation results in i. Causation of days andnights; ii. A difference of one hour between two meridians which are 15° apart; iii. Change in the direction of wind and ocean currents; Rise and fall of tides everyday. iv. The longest day in North Hemisphere is June 21, while shortest day is on 22 Dec(Vice-versa in S.Hemisphere).
• Days and nights are almost equal at the equator. Earth Revolution
• It is earth‘s motion in elliptical orbit around the sun. Earth‘s average orbital velocity is 29.79 Kilometers/s.
• Takes 365 days, 5 hrs, 48 min and 45.51 sec. It results in one extra day every fourth year. Earth Eclipses Earth Lunar Eclipse· When earth comes between sun and moon. · Occurs only on a full moon day. However, it does not occur on every full moon day because the moon is so small and theplane of its orbit is tilted about 5° with respect to the plane of the earth‘s orbit. It is for this reason that eclipses do not occur every month. · This light is red because the atmosphere scatters the other colors present in sunlight in greater amountsthan it does red. Earth Solar Eclipse Asolar eclipseis a type of eclipse that occurs when theMoon passes between the Sun and Earth, and the Moon fully or partially blocks ("occults") the Sun. This can happen only at new moonThe layering of Earth is categorized as Lithosphere, Asthenosphere, Upper mantle, Lower mantle, Outer core, and the Inner core. The earth's interior has three different layers; they are (i) the crust (ii) mantle and (iii) the core.
Earth's Crust:
All of the Earth's landforms(mountains, plains, and plateaus) are contained within it, along with the oceans, seas, lakes and rivers. There are two different types of crust: thin oceanic crust that underlies the ocean basins and thicker continental crust that underlies the continents. These two different types of crust are made up of different types of rock. The boundary between the crust and the mantle is Mohorovicic Discontinuity.
Earth's Mantle:
It is the thick, dense rocky matter that surrounds the core with a radius of about 2885 km. The mantle covers the majority of the Earth's volume. This is basically composed of silicate rock rich in iron and magnesium. This layer is separated from the core by Gutenberg-Wiechert Discontinuity. The outer and the inner mantle are separated by another discontinuity named Repetti discontinuity.
Earth's Core:
Earth's Core is thought to be composed mainly of an iron and nickel alloy. The core is earth's source of internal heat because it contains radioactive materials which release heat as they break down into more stable substances.
ATMOSPHERE
Atmosphere is a thick gaseous envelope that surrounds the earth and extends thousands of kilometers above the earth's surface. Much of the life on the earth exists because of the atmosphere otherwise the earth would have been barren. Nitrogen and Oxygen comprise 99% of the total volume of the atmosphere. Structure of the Atmosphere The atmosphere consists of almost concentric layers of air with varying density and temperature.
Troposphere:
• Lowest layer of the atmosphere.
• The height of troposphere is 16 km thick over the equator and 10 km thick at the poles.
• All weather phenomena are confined to troposphere (e.g. fog, cloud, frost, rainfall, storms, etc.)
• Temperature decreases with height in this layer roughly at the rate of 6.5° per 1000 metres, which is callednormal lapse rate.
• Upper limit of the troposphere is calledtropopause which is about 1.5 km.
Stratosphere
• The stratosphere is more or less devoid of major weather phenomenon but there is circulation of feeble winds and cirrus cloud in the lower stratosphere.
• Jet aircrafts fly through the lower stratosphere because it provides perfect flying conditions.
• Ozone layer lies within the stratosphere mostly at the altitude of 15 to 35 km above earth's surface.
• Ozone layer acts as a protective cover as it absorbs ultra-voilet rays of solar radiation.
• Depletion of ozone may result in rise of temperature of ground surface and lower atmosphere.
• Temperature rises from-60°C at the base of the stratosphere to its upper boundary as it absorbs ultra-voilet rays.
• Upper limit of the Stratosphere is called stratopause.
Mesosphere
• Mesosphere extends to the height of 50-90 km.
• Temperature decreases with height. It reaches a minimum of-80°C at an altitude of 80-90 km
• The upper limit is called mesopause.
Thermosphere
• It lies at 80 km to 640 km above the earth's surface.
• It is also known as ionosphere.
• Temperature increases rapidly with increasing height.
• It is an electrically charged layer. This layer is produced due to interaction of solar radiation and the chemicals present, thus disappears with the sunset.
• There are a number of layers in thermosphere e.g. D-layer, E-layer, F-layer and G-layer.
• Radio waves transmitted from earth are reflected back to the earth by these layers. e) Exosphere
• This is the uppermost layer of the atmosphere extending beyond the ionosphere.
• The density is very low and temperature becomes 5568°C.
• This layermerges with the outer space. About Ionosphere At heights of 80 km (50 miles), the gas is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion. This portion of the atmosphere is ionized and contains plasma which is referred to as the ionosphere. The Ultraviolet (UV), X-Ray and shorter wavelengths of solar radiation ionizes the atmosphere. The ionosphere is broken down into the D, E and F regions. PRESSURE AND WIND BELTS Air pressure is thus defined as total weight of a mass of column of air above per unit area at sea level. The amount of pressure exerted by air at a particular point is determined by temperature and density which is measured as a force per unit area.
• Aneroid Barometer-It is the most common type barometer used in homes.
OCEANS
Arctic Ocean
The Arctic Ocean is the smallest of the world's five oceans. The Northwest Passage (US and Canada) and Northern Sea Route (Norway and Russia) are two important seasonal waterways. It is abody of water between Europe, Asia, and North America, mostly north of the Arctic Circle.
Lowest point: From Basin Major chokepointis the Southern Chukchi Sea
Ports and harbors: Churchill (Canada), Murmansk (Russia), Prudhoe Bay (US)
Atlantic Ocean
The Atlantic Ocean is the second largest of the world's five oceans. The Kiel Canal (Germany), Oresund (Denmark-Sweden), Bosporus (Turkey), Strait of Gibraltar (Morocco-Spain), and the Saint Lawrence Seaway (Canada-US) are important strategic access waterways. It is a body of water between Africa, Europe, the Southern Ocean, and the Western Hemisphere.It includesincludes Baltic Sea, Black Sea, Caribbean Sea, part of the Drake Passage, Gulf of Mexico, Mediterranean Sea, and other tributary water bodies.
Lowest point: Milwaukee Deep in the Puerto Rico Trench Major chokepointsinclude the Dardanelles, Strait of Gibraltar, access to the Panama and Suez Canals. TheEquatordivides the Atlantic Ocean into the North Atlantic Ocean and South Atlantic Ocean.Kiel Canal and Saint Lawrence Seawayare two important waterways.
Indian Ocean
The Indian Ocean is the third largest of the world's five oceans. Four critically important access waterways are the Suez Canal (Egypt), Bab-el Mandeb (Djibouti-Yemen), Strait ofHormuz (IranOman), and Strait of Malacca (Indonesia-Malaysia). It is abody of water between Africa, the Southern Ocean, Asia, and Australia. It includes Andaman Sea, Arabian Sea, Bay of Bengal, Flores Sea, Gulf of Aden, Gulf of Oman, Java Sea, Red Sea, Strait of Malacca, Timor Sea, and other tributary water bodies.
Pacific Ocean
The Pacific Ocean is the largest of the world's five oceans. Strategically important access waterways include the La Perouse, Tsugaru, Tsushima, Taiwan, Singapore, and Torres Straits. It is body of water between the Southern Ocean, Asia, Australia, and the Western Hemisphere. It includes Bali Sea, Bering Sea, Coral Sea, East China Sea, Gulf of Alaska, Philippine Sea, Sea of Japan, Sea of Okhotsk, Tasman Sea, and other tributary water bodies. Lowest point:Challenger Deep in the Mariana Trench.
Themajor chokepointsare the Bering Strait, Panama Canal, Luzon Strait, and the Singapore Strait; the Equator divides the Pacific Ocean into the North Pacific Ocean and the South PacificOcean.
Ports and harbors:Bangkok (Thailand), Los Angeles (US), Manila (Philippines), Pusan (South Korea), San Francisco (US), Seattle (US), Shanghai (China), Singapore, Sydney (Australia), Vladivostok (Russia).
SOUTHERN OCEAN
The Southern Ocean is the fourth largest of the world's five oceans. It is a body of water between 60 degrees south latitude and Antarctica. It includes Amundsen Sea, Bellingshausen Sea, part of the Drake Passage, Ross Sea, a small part of the Scotia Sea, Weddell Sea, and other tributary water bodies.
Lowest point: southern end of the South Sandwich Trench. The major chokepointis the Drake Passage between South America and Antarctica. 6778
Ports and harbors: McMurdo, Palmer, and offshore anchorages in Antarctica.
TIDES
The tide isthe periodic rise and fall of the sea levels caused by the combined effects of the gravitational forces exerted by the Moon and Sun and rotation of the earth. Most places in the ocean usually experience two high tides and two low tides each day (semidiurnal tide), but some locations experience only one high and one low tide each day (diurnal tide). The times and amplitude of the tides at the coast are influenced by the alignment of the Sun and Moon, by the depth of the ocean, and by the shape of the coastline and near-shore bathymetry. When the moon exerts gravitational force on the earth the tidal bulge moves out and causes high tide. Simultaneously on the side opposite to that place on the earth i.e. just at 180° to it, also experiences the tidal bulgedue to reactionary force (centrifugal) of the gravitational (centripetal) force. Thus two tides are experienced twice at every place on the earth's water surface within 24 hours. Due to the cyclic rotation of the earth and moon, the tidal cycle is 24 hours and 52 minutes long.
