Upsc-Psc Exam Tricks Blog: Geography

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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. 
 
 
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The Origin Of Earth !</div>
 
The formation of Earth occurred as part of the formation of the Solar System. It started as a large 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 the mass 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 Lsta 21⁄2 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). 
• Biggest Planet : Jupiter 
• Smallest Planet : Mercury 
 
Solar System Some Facts 
 
• 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 
 
Earth Latitude and Longitude ! 
 
Earth Latitude :- 
• Imaginary lines drawn parallel to the equator. Measured as an angle whose apex is at the centre of the earth. 
• The equator represents 0° latitude, while the North Pole is 90° N and the South Pole 90° S 
• 231⁄2° N represents Tropic of Cancer while 231⁄2° S represents Tropic of Capricorn. 
• 661⁄2° N represents Arctic Circle while 661⁄2° S represents Antarctic Circle. 
• There are total 181 latitudes including the equator. Each parallel of latitude is a circle, but they are not equal. 
• The circle becomes smaller towards the poles. Equator is the  Greatest Circle‘ that can be drawn on the earth‘s surface. 
• The distance between any two parallels of latitude is always equal. 1 degree lat. = 111km. Earth Longitude 
• It is the angular distance measured from die centre of the earth. On the globe the lines of longitude are drawn as a series of semicircles that extend from the North Pole to the South Pole through the equator. They are also called meridians. 
• The distance between any two meridians is not equal. At the equator, 1 degree = 111 km. At 30°N or S, it is 96.5 km. It goes on decreasing this way until it is zero at the poles. 
• There are 360 meridians of longitude. The prime meridian is a longitude of 00 at Greenwich near London. 
• This meridian is taken by geographers to divide the earth into the eastern and the western hemispheres. 
• Each meridian of longitude is a semi-circle. 180° meridian (International Date Line) lies exactly opposite to 0° meridian. Such points are called Antipodal Points. 
• The earth is divided into 24 longitudinal zones, each being 15° or 1 hour apart in time (4 minutes / degree). Longitude and Time 
• Places that are on the same meridian have the same local (sun) time. Since the earth makes one complete revolution of 360° in 24 hours, it passes through 15° in one hour or 1° in 4 minutes. 
• The earth rotates from west to east, hence places east of Greenwich see the sun earlier and gain time whereas places west of Greenwich see the sun later and lose time. 
• India, whose longitudinal extent is approx. 30°, has adopted only one time zone, selecting the 82.5°E for the standard time which is 5 hours and 30 minutes ahead of GMT (Greenwich Mean Time).International Date Line 
• It is the 180° meridian running over the Pacific Ocean, deviating at Aleutian Islands, Fiji, Samoa and Gilbert Islands. It is a zig-zag line 
• Travelers crossing the Date Line from west to east (i.e., from Japan to USA) repeat a day and travelers crossing it from east to west (i.e., from USA to Japan) lose a day. 
 
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). 
• passing through the Royal Observatory 
 
• Revolution of the earth results in :- 
 
i. Change of seasons 
ii. Variation in the lengths of days and nights at different times of the year 
iii. Shifting of wind belts 
iv. Determination of latitudes. 
 
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. 
 
•  This light is red because the atmosphere scatters the other colors present in sunlight in greater amounts than it does red. Earth Solar Eclipse A solar eclipse is 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 moon The 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. 
 
a) 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. 
 
b) 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. 
 
c) 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. The core is divided into two different zones. The outer core is a liquid because the temperatures there are adequate to melt the iron-nickel alloy. However, the inner core is a solid even though its temperature is higher than the outer core. Here, tremendous pressure, produced by the weight of the overlying rocks is strong enough to crowd the atoms tightly together and prevents changing it to the liquid state. 
 
a) An earthquake is the sudden release of strain energy in the Earth's crust resulting in waves of shaking that radiate outwards from the earthquake source. 
b) The point at the surface directly above the focus is called the earthquake epicentre. 
c) When the earth moves in an earthquake, it can cause waves in the ocean, and if a wave grows large enough, it's called a "tsunami". 
e) Earthquakes are measured with a seismometer. The magnitude of an earthquake, and the intensity of shaking,is measured on a numerical scale. On the scale, 3 or less is scarcely noticeable, and magnitude 7 (or more) causes damage over a wide area. The point of origin of earthquake is called 
Seismic focus. The point on the earth‘s surface vertically above the earth‘s surface is called Epicentre. 
f) The passage of earthquake waves is recorded by Seismograph. The magnitude of waves is measured on Richter‘s scale. For measurement of the intensity of the earthquake (damage caused), the Modified Mercalli Intensity Scale is used. 
 
Distribution of Earthquakes 
 
a) Around the Pacific Ocean along a belt of volcanoes known as the Ring of Fire. 68 per cent of the volcanoes are experienced in this region. 
b) From the middle of Asia (Himalayas, Caspian Sea) through the Mediterranean Sea to West Indies. 21 per cent earthquakes are experienced in the region. 
c) Mid-Atlantic ridge belt which accounts for 11 percent of the earthquakes. 
 
There are two types of seismic waves, body wave and surface waves. 
 
• Body waves travel through the interior of the Earth. They follow ray paths refracted by the varying density and stiffness of the Earth's interior which in turn, vary according to temperature, composition, and phase. 
 
Body waves are divided as 
 
P-WAVES (Primary Waves) are compression waves that are longitudinal in nature. These waves can travel through any type of material, and can travel at nearly twice the speed of S waves. 
 
S-WAVES (Secondary Waves) are shear waves that are transverse in nature. These waves typically follow P waves during an earthquake and displace the ground perpendicular to the direction of propagation. S waves can travel only through solids, as fluids (liquids and gases) do not support shear 
stresses. S waves are slower than P waves, and speeds are typically around 60% of that of P waves in any given material. 
 
• Surface waves are analogous to water waves and travel along the Earth's surface. They travel slower than body waves. 
 
There are two types of surface waves: Rayleigh waves, also called ground roll, are surface waves 
 
that travel as ripples with motions that are similar to those of waves on the surface of water. 
 
EARTHQUAKES :- 
 
TYPES OF SEISMIC WAVES 
 
Love waves are surface waves that cause circular shearing of the ground. They are named after A.E.H. Love, a British mathematician who created a mathematical model of the waves in 1911. They usually travel slightly faster than Rayleigh waves, 
about 90% of the S wave velocity, and have the largest amplitude. 
 
The asthenosphere separates the strong, solid rock of the uppermost mantle and crust above from the remainder of the strong, solid mantle below. The combination of uppermost mantle and crust above the asthenosphere is called the lithosphere. The lithosphere is free to move (glide) over the weak asthenosphere. The tectonic plates are, in fact, 
 
lithospheric plates. 
 
1. Primary Waves (P-Waves): 
a) Travel from the point of happening by the displacement of surrounding particles. 
b) They are transmitted through solids, liquids and gases. 
c) Travels fastest. 
 
2. Secondary Waves (S-Waves): 
a. Travels through solids only. 
b. Thus they cannot pass through core. 
 
3. Surface Waves or Long Waves (L-Waves): 
a) Travels on earth‘s surface and causes maximum destruction. 
b) They are recorded after the P and S waves. 
 
A volcano is generally a conical shaped hill or mountain built byaccumulations of lava flows, and volcanic ash. About 95% of active volcanoes occur at the plate subduction zones and at the mid-oceanic ridges. Subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge. Regions where this process occurs are known as sub-duction zones. The other 5% occur in areas associated with lithospheric hot spots. It is believed that hot spots are caused by plumes of rising magma that have their origin within the asthenosphere. 
 
Geologists have classified five different types of volcanoes. This classification is based on the geomorphic form, magmachemistry, and the explosiveness of the eruption. The least explosive type of volcano is called a basalt plateau. These volcanoes produce a very fluid basaltic magma with horizontal flows. Deposits of these volcanoes can be as thick as 1800 meters. Large basalt plateaus are found in the Columbia River Plateau, western India, northern Australia, Iceland, Brazil, Argentina, and Antarctica. Some basaltic magmas can produce very large slightly sloping volcanoes, 6 to 12°, that have gently flowing magmas called shield volcanoes Shield volcanoes can be up to 9000 meters tall. The volcanoes of the Hawaiian 
 
Islands are typical of this type. 
 
A cinder cone is a small volcano, between 100 and 400 meters tall, made up of exploded rock blasted out of a central vent at a high velocity. These volcanoes develop from magma of basaltic to intermediate composition. They form when large amounts of gas accumulate within rising magma. Examples of cider cones include Little Lake Volcano in California and Paricuti Volcano in Mexico. 
Composite volcanoes are made from alternate layers of lava flows and exploded rock. Their height ranges from 100 to 3500 ... 
 
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Geography Planets - Explanation ! Geography

Nebular Theory ! There are many ideas about the formation and evolution of the Solar System. The accepted idea is that 4.6 billion years...

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Planets - Explanation ! Geography

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