World Geography

World Geography

Earth Movements

• The Earth also 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.

Earth Rotation

• 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:

1. Causation of days and nights;
2. A difference of one hour between two meridians which are 15° apart;
3. Change in the direction of wind and ocean currents;

• Rise and fall of tides everyday.
• 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.
• Revolution of the earth results in:

1. Change of seasons
2. Variation in the lengths of days and nights at different times of the year
3. Shifting of wind belts
4. Determination of latitudes.

• Inclined Axis: The axis is an imaginary line running from north to south and passing through the centre of the earth. It always remains inclined at an angle of 66½° to the plane of the earth’s orbit, and is tilted 23½° from a line perpendicular to this plane. The two facts, i.e., a fixed angle of the earth’s axis to the plane of the orbit and the axis always pointing in the same direction, when combined with the earth’s movements, results in varying lengths of days and nights, seasonality and changes in the altitude of sun at different times of the year.
• Earth Seasons are periods into which the year can be divided as a result of the climatic conditions, largely due to the changes in the duration and intensity of solar radiation.

Earth Seasons

• Spring: On March 21, the sun is directly overhead the equator. This is the season of spring in the northern hemisphere.
• Summer: On June 21, the sun is directly overhead the Tropic of Cancer. Thus, the northern hemisphere experiences summer.
• Autumn: On September 23, the sun returns to the equator, and the northern hemisphere experiences autumn.
• Winter: On December 22, the sun is at the Tropic of Capricorn, and the northern hemisphere experiences winter

Earth Some Important Facts

•  Age  4,60,00,00,000 years
• Total surface area  51,01,00,500 Square Kilometers
• Land area (29.08%)  14,89,50,800 Square Kilometers
• Water area (70.92%) 36,11,49,700 Square Kilometers
• Mean density  5.52 gm. per cc
• Equatorial diameter  12,755 Kilometers
• Polar diameter  12,712 Kilometers
• Escape velocity  11.2 Kilometers/sec
• Mass  5.880 1024 kg
• Volume 10,83,20,88,40,000 kg3
• Distance from Moon  3,82,200 Kilometers
• Highest place on Earth  Mount Everest (8,850 m)
• Deepest point in Ocean  Challenger Deep in Mariana Trench in Pacific Ocean near Philippines (11,033 m deep)
• Deepest point on Land  Dead Sea (396 m deep)
• Rotation time  23 hrs, 56 min, 40.91 sec
• Revolution time  365 days, 5 hrs, 48 min, 45.51 sec Satellite  1 (Moon)
• Tilt of axis from Orbital Plane  23° 27
• Distance from Sun  14,94,07,000 Kilometers
• Equatorical circumference  40,075 Kilometers
• Polar circumference  40,024 Kilometers
• Average Ocean depth  3,554 m
• Date of perihelion (minimum distance from Sun) Jan 3
• Date of aphelion (maximum distance from Sun)  July 4
• Orbital circumference  924,375,700 Kilometers
• Average Orbital speed  29.783 Kilometers/sec. (107,218 Kilometers/h)
• Minimum surface temperature  88° C
• Mean surface temperature  14° C
• Maximum surface temperature  58° C
• Earth Latitude and Longitude

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 the plane 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.
• Can last up to one hour 40 minutes. The moon does not become completely dark during most lunar eclipses. In many cases, it becomes reddish. The earth’s atmosphere bends part of the sun’s light around the earth and towards the moon.
• This light is red because the atmosphere scatters the other colors present in sunlight in greater amounts than it does red.

Earth Solar Eclipse

• When moon comes between sun and earth.
• Can be partial or total.
• Occurs only on a new moon day when the moon is in line with the sun. However, due to the inclination of the moon’s orbit, a solar eclipse doesn’t occur on every new moon day.

Internal Structure of Earth

The Crust of Earth

• It is the outermost and the thinnest layer of the earth’s surface, about 8 to 40 km thick. The crust varies greatly in thickness and composition – as small as 5 km thick  in some places beneath the oceans, while under some mountain ranges it extends up to 70 km in depth.
• The crust is made up of two layers- an upper lighter layer called the Sial (Silicate + Aluminium) and a lower density layer called Sima (Silicate + Magnesium).
• The average density of this layer is 3 gm/cc.

The Mantle of Earth

• This layer extends up to a depth of 2900 km.
• Mantle is made up of 2 parts: Upper Mantle or Asthenosphere (up to about 500 km) and Lower Mantle.
• Asthenosphere is in a semi-molten plastic state, and it is thought that this enables the lithosphere to move about it. Within the asthenosphere, the velocity of seismic waves is considerably reduced (Called ‘Low Velocity Zone’).
• The line of separation between the mantle and the crust is known as Mohoviricic Discontinuity.

The Core of Earth

• Beyond a depth of 2900 km lies the core of the earth.
• The outer core is 2100 km thick and is in molten form due to excessive heat out there. Inner core is 1370 km thick and is in plastic form due to the combined factors of excessive heat and pressure. It is made up of iron and nickel (Nife) and is responsible for earth’s magnetism. This layer has the maximum specific gravity.
• The temperatures in the earth’s core lie between 2200°c and 2750°c.
• The line of separation between the mantle and the core is called Gutenberg-Wiechert Discontinuity.

Note: Temperature Inside the Earth: In the first 100 km, 12° increase per km. In the next 300 km, 2° increase per km. After that it is 1° increase per km.

Composition of Earth

• Made up of over 100 elements.
• The following 8 are important:

Oxygen  46.5%, Silicon  27.72%,   Aluminium  8.13%, Iron  5 01%, Calcium  3.63%, Sodium  2.85%, Potassium  2.62%, Magnesium 2.09%, Magnesium 2.09%

Earth Rocks

Any aggregate of material particles that forms part of the earth’s crust is called a rock.

There are 3 major types of rock types:

Igneous Rocks

• Formed by the solidification of molten magma from the interior of the earth.
• Most abundant of the three types of rocks (95%).
• They do not occur in layers. Most of them are crystalline and do not contain fossils.
• All other types of rocks originate from these rocks, thus called Primary rocks.

They are classified on several grounds as mentioned below:

1. On the basis of mode of occurrence

• Intrusive Igneous Rocks: They are formed by the solidification of magma beneath the earth’s surface. They are further divided into plutonic and hypabyssal igneous rocks. Plutonic rocks cool deep beneath the earth. E.g., Granite. Hypabyssal rocks cool just beneath the earth’s surface. E.g., Batholith, laccolith, phacolith, sills, dykes, etc.
• Extrusive Igneous Rocks: They are formed due to cooling and solidification of hot and molten lava at the earth’s surface. E.g., Basalt, gabbro, etc.

2. On the basis of Silica Content

• Acidic igneous rocks having more silica. E.g. Granite.
• Basic igneous rocks having less silica. E.g. Gabbro.

Sedimentary Rocks

• Made up of weathered remains of igneous rocks. Also contains fossils of plants and animals.
• Comprise only about 5% of the earth’s crust but cover about 75% of the total land surface.
• The layers of sedimentary rocks hold all reserve of coal, oil and natural gas.
• Also known as Stratified Rocks because of the layers.
• Sedimentary rocks fall into three main groups:

1. Mechanically Formed: These are called clastic sedimentary rocks; the sediments are largely derived from pre-existing rocks that have been broken down and then transported by water, wind or ice to form rocks.
2. Organically Formed Rocks: These rocks are derived from remains of plants (e.g. peat, lignite, bituminous coal), or animals (e.g., chalk and coral).
3. Chemically Formed: E.g., Gypsum, salt rock, etc.

Metamorphic Rocks

• Sometimes igneous or sedimentary rocks metamorphize or change due to great ‘pressure, intense temperature or the action of water and chemical activity.
• Examples of metamorphic rocks formed from different rocks are:

Metamorphic Rock     Made From

• Slate               Shale and mudstone
• Quartzite       Sandstone
• Gneiss            Granite
• Marble          Limestone, dolomite or chalk
• Schist             Shale
• Anthracite    Coal

Earth Mountains

Types of Mountains

Fold Mountains of the World

• They are formed when the rocks of the crust of the earth folded under stress, mainly by forces of compression (as a result of series of earthquakes).
• E.g. – All big mountain systems: Himalayas, Alps, Andes, Rockies, Atlas, etc.
• On the basis of age, fold mountains are grouped into: Young / New Fold Mountains
• Came into existence after the continental drift. E.g. Himalayas, Andes, Rockies, Alps. Himalayas are regarded the youngest mountains in the world.

Old Mountains

• They belong to pre-drift era, then subjected to denudation and uplift; many faults were formed; occur as relict mountains today. E.g. Pennines (Europe), Appalachians (US), Aravallis (India).

Block Mountains of the World

• These are formed when great blocks of earth’s crust may be raised or lowered. During the uplift of structural mountains, sometimes magma flows upwards into the crust.
• On its cooling and hardening beneath the surface, it contracts and the overlying rock may crack into large blocks moving up or down. An intense folding of rocks is generally followed by faulting of strata due to horizontal forces of tension.
• The land between the two parallel faults either raises forming Block Mountains or Horsts, or subsides into a depression termed as Rift Valley or Graben.
• E.g.: Narmada, Tapti and Damodar valley in India, the Vosges in France and Black forest in Germany (through which Rhine River flows).

Volcanic Mountains of the World

• Formed as a result of volcanic eruption & the outflow of lava (through crater, the opening). Also called Mountains of Accumulation. Have a gentle slope.
• E.g.: Cotopaxi in Andes, Vesuvius and Etna in Italy, Fujiyama in Japan, Mauna Loa and Kilauea (Most active volcano) in Hawaii, Ojos del Salado in Argentina / Chile (Highest active volcano), Popocatepeti in Mexico, Raineer of Washington, Stromboli in Mediterranean (called Lighthouse of the Mediterranean), Mirapi and Krakatao in Indonesia, etc.

Relict Mountains

• Sometimes, the mountains are carved out as a result of erosion of plateaus & high planes by various agents of erosion.
• E.g., Highlands of Scotland, Sierras of Spain, Catskill mountains of New York and Nilgiri, Parasnath, Girnar, Rajmahal of India.

Major Mountain Ranges of the World

• Andes                                                           South America                      6,960
• Himalayas-Karakoram-Hindukush South                                                 Central Asia 8,850
• Rockies                                                         North America                      4,401
• Great Dividing Range                                 East Australia                        2,228
• Western Ghats                                            Western India                       2,637
• Caucasus                                                      Europe, Asia                          5,642
• Alaska                                                           USA                                         6,194
• Alps                                                               Europe                                   4,808
• Apennines                                                   Europe                                   2,912
• Ural                                                               Asia                                         1,895
• Pennines                                                      Europe                                   893
• Pyrenees                                                      Europe                                   3,404
• Appalachian                                                 North America                      2,040

Earth Moon

• Moon Circumference: 11,000 km. Diameter: 3475 km. Gravitational pull: 1/6th of Earth.
• Its orbit around earth is elliptical. The maximum distance (Apogee) of the moon from the earth is 406,000 km and the minimum distance (Perigee) is 364,000 km. the average distance is 3,82,200 km.
• All other satellites (except Charon) have sizes below 1/8th the size of mother planets. But moon is about 1/4th the size of earth.
• Takes 27 days, 7 hrs, 43 min and 11.47 sec to complete one revolution around earth.
• Rotates on its axis in exactly the same time as it takes to complete one revolution. That is why we see only one side of the moon (only 59% of its surface).
• To our unaided vision, moon seems to be made-up of bright and dark patches. The bright parts are the mountains and highlands, while the darker patches are low – lying planes.
• The highest mountains on moon are Liebnitz Mountains, which are 10,660 m high. They are situated at moon’s South Pole.
• Moon has no atmosphere, no twilight and no sound.
• Moonlight takes 1.3 sec to reach earth.
• It has a low albedo (amount of sunlight reflected). It reflects only 7% and the rest is absorbed (Earth : 30%, Venus: 70%)
• Neil Armstrong and Buzz Aldrin reached moon on July 20, 1969 on Apollo XI and set the foot on. July 21, 1969 (landing spot is called Sea of tranquility).

Moon: Some Important Facts

• Moon Distance from Earth – 3,82,200 km
• Moon Diameter – 3,475 km
• Moon Mass (with respect to Earth) – 1 : 8.1
• Ratio of Gravitational Pull of Moon and Earth – 1 : 6
• Part of Moon not visible from Earth – 41%
• Maximum distance from Earth (Apogee) – 4,06,000 km
• Minimum distance from Earth (Periqee) – 3,64,000 km
• Revolution period around Earth – 27 days, 7 hrs, 43 min and 11.47 sec
• Rotation period – 27 days, 7 hrs, 43 min and 11.47 sec
• Atmosphere – Absent
• Highest mountain – 35,000 ft (Leibnitz Mts)
• Time taken by moonlight to reach Earth – 1.3 sec
• Rotation speed – 3,680 kmph
• Speed of revolution around Earth – 3,680 kmph

Oceans of the World

Oceans cover about 70% of the Earth’s surface. The oceans contain roughly 97% of the Earth’s water supply.

The oceans of Earth are unique in our Solar System. No other planet in our Solar System has liquid water (although recent finds on Mars indicate that Mars may have had some liquid water in the recent past). Life on Earth originated in the seas, and the oceans continue to be home to an incredibly diverse web of life.

The oceans of Earth serve many functions, especially affecting the weather and temperature. They moderate the Earth’s temperature by absorbing incoming solar radiation (stored as heat energy). The always-moving ocean currents distribute this heat energy around the globe. This heats the land and air during winter and cools it during summer.

The Earth’s oceans are all connected to one another. Until the year 2000, there were four recognized oceans: the Pacific, Atlantic, Indian, and Arctic. In the Spring of 2000, the International Hydrographic Organization delimited a new ocean, the Southern Ocean (it surrounds Antarctica and extends to 60 degrees latitude).

There are also many seas (smaller branches of an ocean); seas are often partly enclosed by land. The largest seas are the South China Sea, the Caribbean Sea, and the Mediterranean Sea.

Rank      Ocean                         Notes

1. Pacific Ocean            Separates Asia and Oceania from the Americas
2. Atlantic Ocean          Separates the Americas from Eurasia and Africa
3. Indian Ocean             Washes upon southern Asia and separates Africa and Australia
4. Southern Ocean       Sometimes considered an extension of the Pacific, Atlantic and Indian Oceans, which encircles Antarctica
5. Arctic Ocean         Sometimes considered a sea of the Atlantic, which covers much of the Arctic and washes upon northern North America and Eurasia

• Sahara – N. Africa (Includes the Libyan and the Nubian Desert)
• Australian – Australia (Includes Gibson, Simpson, Victorian, Great Sandy)
• Arabian – Arab Countries (Includes Rub’al Khali & An-Nafad of S. Arabia and Dast-e-Lut & Dast-e-Kavir of Iran)
• Kalahari – Africa (mainly in Botswana)
• Gobi – Mongolia
• Atacama – Central Chile
• Patagonian – Argentina
• Nabib – Namibia
• TaklaMakan – Sinkiang, China
• Karakum – Turkmenistan
• Sonoran – Arizona and California (USA)
• Thar – India

Continents of the Earth

Did you know that approximately 70% of the Earth’s surface is covered by water alone and the other 30% are covered by land? This land has been divided into seven main areas. Each area is called a continent.

Most of this land lies above the Equator. The Equator is an imaginary line around the world. It lies exactly halfway between the North and the South Poles.

The seven continents are Asia, Australia, Africa, Antarctica, North America, South America and Europe. It is seen that each continent has a special shape. Some of these continents are connected while the water separates others.

Asia

Asia being the largest of the continents covers around one-third of the world’s total land area. Asia is known for its vast size and incomparable character. It stretches all the way east from Japan to the Southeast Arabian Peninsula, which is more than 8500 kilometers away.

It is interesting to see the geographical composition of Asia. It encompasses the entire climate and expanse, be it the equatorial rain forest or the arctic tundra. We also get to see the highest and the lowest points of the Earth’s surface in Asia. The highest being, Mount Everest (8,848 meters) and the lowest is the shore of the Dead Sea (397 meters below sea level).

Africa

Africa is the second largest of the continents, covers around 22% of the world’s land area. The Equator intersects it and the expansive landmass covers the Sahara, which is the world’s largest desert, and the Nile, the longest river on earth, as well as 53 nations.

Most of Africa is a desert region. This continent is basically divided into three regions, which are the Northern Plateau, the Central and Southern Plateau, and the Eastern Highlands. This includes plains, swampy coastal regions, lush tropical forests with Savannah’s and hilly plateaus inland. Africa is famous for it’s diamond, gold, uranium and copper mining.

North America

North America is around twice the size of Europe. It stretches from the vast wintry environment of the Arctic regions to the Yucatan Peninsula. America is sort of wedge shaped featuring an exceedingly irregular coastline with many prominent offshore islands, including Greenland, which is the largest island in the world. It is basically divided into five geographical regions. North America has large deposits of many important minerals, including iron ore, copper, nickel, and uranium. Coal is also found in eastern and western Canada and the United States. World’s greatest deposits of Petroleum and Natural Gas are seen in the State of Mexico.

South America

South America is the fourth largest continent of the world although it contains less than 12% of the world’s population.

The Andes, world’s second largest mountain range is seen in South America. The second largest river- Amazon also runs through South America. The lowland consists mainly of the Amazon Basin, which is covered in the equatorial region. These areas are of the wet tropical climate and have a dense cover of rain forest. The largest forest area in the world is seen in South America.

South America has diverse mineral resources, like gold, silver, iron, bauxite, tin, lead and zinc many of which have not been thoroughly exploited.

Antarctica

Antarctica the sixth largest of the continents, is ice bound through out the year. Penguins and seals, accompanied by a few invertebrates such as mites and ticks—the only land animals that can tolerate the low temperatures, primarily inhabit it.

Antarctica is a true desert due to its extreme cold climate making it the coldest, windiest, and driest continent. It’s average temperature is around -50°C (-58°F), and the land is swept by hurricanes and the annual rainfall is only around 50 millimeters a year.

This continent has no native civilization but the United Kingdom, Norway, France, Australia, New Zealand, Chile, and Argentina have made territorial claims. Due to the climate it makes it impossible for people to settle down here.

A current critical environmental issue concerning Antarctica is its ozone shield, which protects the earth’s surface from harmful ultraviolet radiation. Measurements indicate that the ozone layer above Antarctica has been reduced to a dangerous level.

Europe

Europe is the fifth largest of the continents. It is also conventionally known as “Europa”. Europa was the daughter of Phoenix in Greek mythology. Some say it is possibly from “Ereb”, a Phoenician word for sunset.

The Ural Mountains, the Ural River, part of the Caspian Sea, and the Caucasus Mountains forms the main boundary between Europe and Asia. Lots of geographers also see the two continents as one and call it EURASIA. Europe has a more or less a radial pattern of drainage. Most streams flow outward from the core of the continent.

A wide variety of mineral resources are found in Europe, including coal, petroleum and natural gas, copper, lead, and tin.

Australia

Australia is the smallest of the seven continents. The interiors of the continent are predominantly plains. The Southeast and the Southwest plains are the most densely settled areas of Australia. The climate of Australia is variable, but weather extremes are rare. The Northern part of Australia has a monsoon sort of climate while in the south it is temperate.

Australia is known for it’s vast wildlife with rare species and it’s known as the land of the kangaroos. Aborigines are the original inhabitants of Australia. Australians are known to have an ethnic sort of origin.

One of the interesting features of Australia is the “Great Barrier Reef”, which is the world’s largest coral reef.