The Prehistoric Period
- The prehistoric period in the history of mankind can roughly be dated from 200000 BC to about 3500-2500 BC when the first civilizations began to take shape. The history of India is no exception.
- The first modern human beings or the Homo sapiens set foot on the Indian subcontinent anywhere between 200000 BC and 40000 BC and they soon spread throughout a large part of the subcontinent, including peninsular India.
- They continuously flooded the Indian subcontinent in waves after waves of migration from what is present-day Iran. These primitive people moved in groups of few ‘families’ and lived mainly on hunting and gathering.
The age when the prehistoric man began to use stones for the utilitarian purpose is termed as the Stone Age.
The Stone Age is divided into three broad divisions —
- Paleolithic Age or the Old Stone Age (100000-10000 BC),
- Mesolithic Age or the Middle Stone Age (9000 BC-4000 BC) and
- the Neolithic Age or the New Stone Age (4000 BC-1800 BC)
on the basis of the specialization of the stone tools, which were made during that time.
Paleolithic or Old Stone Age (100000-10000 BC)
- The human beings living in the Paleolithic Age were essentially food gatherers and depended on nature for food.
- The art of hunting and stalking wild animals individually and later in groups led to these people making stone weapons and tools.
- First, crudely carved out stones were used in hunting, but as the size of the groups began to increase and there was a need for more food, these people began to make “specialized tools” by flaking stones, which were pointed on one end.
- These kinds of tools were generally used to kill small animals and for tearing flesh from the carcass of the hunted animals. The basic technique of making these crude tools was by taking a stone and flanking its sides with a heavier stone.
- These tools were characteristic of the Paleolithic Age and were very rough. By this time, human beings had come to make and use fire.
Mesolithic Age or Middle Stone Age (9000-4000BC)
- In the Mesolithic Age, the stone tools began to be made more pointed and sharp. To ensure a life that had the abundance of food and clothing, the stone tools began to appear in increasingly specialized way.
- The simple handheld stone tools were now attached to thick branches from trees with a rope made from animal skin and sinew.
- These tools are known as hand axes, which could be flung at fast-moving animals from a distance. Apart from hand axes, they also produced crude stone-tipped wooden spears, borers, and burins.
- This period also saw the domestication of animals and graving of wild varieties of crops. Because of farming, small settlements began to take shape.
- Archeological excavations have unearthed Mesolithic sites in the Chota Nagpur area of central India and the areas south of the Krishna River.
- The famous Bhimbetka caves near Bhopal belong to the Mesolithic Age and are famous for their cave paintings. The exact date of these paintings is not certain, but some of the paintings are as old as 12,000 years.
- The prehistoric artist used natural white and red pigments in depicting the various themes, which were close to his heart and sustenance.
Neolithic Age or New Stone Age (4000-1800 BC)
- The Neolithic Age (4000 BC-1800 BC) or the New Stone Age was the last phase of the Stone Age and is characterized by very finely flaked, small stone tools, also known as blades and burins.
- The Neolithic Age also saw the domestication of cattle, horses, and other farm animals. which were used for dairy and meat products? An important invention of this time was the making of the wheel.
- The Neolithic Age quickly gave way to a number of small “’cultures” that were highly technical. These people used copper and bronze to make a range of utilitarian tools. This phase or period is termed as the Chalcolithic Age’(1800BC-I000BC).
- Towards the end of the Neolithic period, metals like bronze and copper began to be used. This was the Chalcolithic phase (1800 BC to 1000 BC).
- Chalcolithic cultures extended from the Chotanagpur plateau to the upper Gangetic basin. Some of the sites of this era are Brahmgiri (near Mysore) and Navada Toli on the N armada.
Plateaus and Its Types
This article clearly explains about the Plateaus, Types of Plateaus and Famous Plateaus of the world.
The term plateau is applied to any fairly flat high land region a tableland or elevated tract of comparatively flat or level land, the surface of which may be uniformly levelled or have broad Summit heights of fairly uniform elevation.
Plateaus are extensive upland areas characterised by at least one side of very steep slope standing well above the neighbouring surface.
Types of Plateaus
Different types of plateaus are
- Intermontane Plateaus
- Piedmont Plateaus
- DomeShaped Plateaus
- Continental Plateaus
- Volcanic Plateaus
- These plateaus are surrounded by hills and mountains from all sides.
- The Tibetan plateau, with a height of about 5000 m, is the most striking example of this type. Other examples are Bolivian plateau, Peruvian plateau, Colombian plateau and Mexican Plateau.
- Plateau formed at the foothill of extensive mountains is called Piedmont plateau.
- Piedmont plateau is surrounded by a mountain range on one side and by plain or ocean on the other side. E.g. Eastern margins of the Appalachians mountains (USA) and Patagonian plateau of South America.
Dome Shaped Plateaus
These plateaus are formed, when the landmass is uplifted in such a manner that the middle portion is raised and the sides are rounded. e.g. Chotanagpur plateau (India) and Ozark (USA) plateau.
- These plateaus are formed either due to the upliftment or extensive spreading of lava on the Earth surface.
- These are very extensive plateaus and are generally away from mountain areas, but are surrounded by oceanic coasts or plains. e.g. Siberian shield and Canadian shield and Brazilian shield.
- These plateaus are formed due to the accumulation of thick layers of basaltic lavas.
- Fissure eruption of volcanoes is the main cause for the formation of these plateaus. Deccan lava plateau of India and Colombian plateau of USA are the best example.
Famous Plateaus of the World
||Between the Himalayas and the Kunlun Mountains
|Plateau of Brazil
||Central-Eastern South America
|Plateau of Columbia
||North-west North America
|Plateau of Bolivia
|Great Basin Plateau
||South of Columbia Plateau, USA
||South of Great Basin-Plateau, USA
This is the brief information about Plateaus and its Types. If you like this article Share or Like it, or if you want to know more comment below.
Mountains and Types of Mountains
Mountains are significant relief features of the second order on the Earth’s surface. Generally, the mountains are more than 1000 m high.
The mountains, whose height is less than 1000 m, called hills. Cordillera includes a general highland formed in a different period and by different processes.
- The word Orogeny comes from two Greek words, viz, oros mean mountain and geny mean creation. It is the primary mechanism, by which mountains are built on the continents. E.g. the Himalayas, Alps, Atlas, Rockies and Andie’s etc.
- The mountains are formed by upward and downward displacement of the Earth’s crust. This displacement is due to folding, faulting and compressional forces of the Earth’s crust. Thus, mountain building can be represented by orogenic belts.
- These are the mobile belts arranged in linear or arcuate tracts that have been subjected to severe deformation and mountain building and are typically found near the edges of the continents. These are two significant aspects of its location.
- The young fold mountain belts found along the Continental margins e.g. Rockies and Andes. Many older mountain belts extend to the ocean and abruptly terminate at the continental margins. E.g. Northern Appalachian and Atlas mountains.
Types of Mountains
On the basis of orogeny, the mountain can be classified as
- Fold mountain,
- Block Mountain and
- Volcanic mountain.
- Fold Mountains formed when a thickly bedded sedimentary layer is subjected t horizontal compressional forces for millions of years. The sediments get bend into up and down -folds. This leads to the formation of anticlines and synclines.
- These mountains are characterised by a more developed system of anticlines and synclines wherein folds are arranged in a wave-like pattern.
Types of Fold Mountains
Fold Mountains are further classified as
- Young Fold Mountains.
- Mature Fold Mountains.
- Old Fold Mountains.
Young Fold Mountains
The Himalayas, the Alps, the Rockies, Andes, Atlas and the Southern Alps.
Mature Fold Mountains
The Pennines, the Appalachians and the Cape range of Southern Africa were formed during the Carboniferous age.
Old Fold Mountains
The high mountains of Scotland and Norway, the Sayan and Stanovai mountains of Russia and the Aravali and Mahadev mountains of India.
- These mountains originate due to tensional force leading to the formation of Rift valley.
- The Block Mountain or Horst represents the upstanding parts of the ground between two faults or on either side of a Rift valley or a Graben.
- The Vosges in France, Black Forest Mountains in Germany and Sierra Nevada in Northern America are the typical examples of Block Mountains.
The continuous deposition of lava over Earth’s surface leads to the formation of a conical peak. It is called volcanic peak. Like mountain Mauna Kea over Hawaii in the Pacific Ocean.
Major Mountain Ranges
|Great Dividing Range
||India, Pakistan, Nepal
Standard Time and International Meridian Conference (IMC)
Standard Time and International Meridian Conference (IMC) are one of the important topics in UPSC Examinations. So, I think this article will surely helpful for your Examinations.
- Before the middle of 19th century, 100’s of different time system were in use, throughout the world, based on the rising of the sun.
- Sir, Sanford Fleming led the fight in Canada for Standard time and for an International agreement upon prime meridian. His Struggle lead, United States, Canada to adopt Standard Time in 1883.
- In 1884 International Meridian Conference (IMC) in Washington DC, to avoid confusion. We follow uniform time throughout the country, such uniform time is based on central meridian of the country or meridian on which most important city is located.
- Such a Central meridian is called Standard Meridian for India, 82 ½° East. Generally central meridian is taken in such a way by that it is divisible by 7½°.
- So that the standard time differs from GMT ( Greenwich Mean Time) by multiples of half an hour.
- Countries which have vast longitude extension do not have a standard single time for the whole country.
- Generally such country goes for more than 1-time zone each approximately 15° of longitude.
- China extends across 4 fifteen degrees zone, the entire nation at least officially observe the time of 120° E meridian close to china’s capital.
International Meridian Conference (IMC) 1884.
- The world was divided into 24 standard time zones each extending over 15° of longitude.
- The local solar time of the Greenwich was chosen as the standard for the entire system.
- The prime meridian (PM) became the centre of a time zone that extends 7½ of longitude both to the west and to the east of the Prime Meridian.
- Similarly, the meridians that are the multiples of 15, both cast and west of the meridian, were set as the central meridians for 23 other time zones, each of which is 15° of longitude in extent.
- 12 zones to the east of Greenwich meridian were designated to be ahead of the time at Greenwich by 1 hour per zone. Similarly, 12 zones to the west of GreenWich are behind.
- In International waters, these time zones are shown exactly 7½ to east and 7½° to the west of the central meridians.
- Over land areas, however, the actual eastern and western boundaries of time zones vary to coincide with appropriate political and economic constraints.
This is the article about Standard time and International Meridian Conference
Precipitation and Types of Precipitation
Precipitation and types of Precipitation.
Before we start, you should have to know about Cloud and Hydrological cycle.
Forces acting on the moving air near the Earth’s surface
There are three forces acting on moving air near the Earth’s Surface. They are
- Pressure Gradients Force (PGF)
- Coriolis Force.
- Forces of Friction.
(1) Pressure gradient force (pgf)
Pressure Gradient Force is the basic activating force for the wind. I.e. it initiates the movement of air.
They are two types
- Gentle Pressure Gradient (slow movement of wind).
- Steep Pressure Gradient (Faster movement of wind).
Pressure Gradient Force attempts to take the air from high pressure zone to low pressure across the isobar in a perpendicular direction.
(2) Coriolis Force
Because of earth rotation, all moving bodies on the earth appear to get deflect.
To account for that apparent deflection the scientists has proposed a force calledCoriolis law (named after French Mathematician – Gespard coriolis).
There is a law about this force – ” ferrels law of deflection “.
Ferrels Law states “the effect of Coriolis force on a moving body – there is an apparent deflection of moving body to its right in the Northern Hemisphere and to its left in the Southern Hemisphere.”
This Coriolis Force is negligible near the equator and it increases towards the pole.
The reason for this lies in the effect that the earth’s speed decreases as we more from Equator to the poles and the rate of this is decreases is a function of Latitude (rate increases towards the pole).
(3) Forces of Friction:
Forces of Fraction
Speed decreases, modifies the direction. The Frictional drag of this Earth’s surface acts both to slowdown wind movement and to modify its direction of Flow.
Zone of Convergence of Air
Zone of Convergence of Air is a Zone where there is net in flow of air. A low pressure zone is a zone of convergence of air.
Zone of Divergence of Air
Zone of Divergence of Air is a zone where there is net out flow of air. A high pressure zone is a zone of divergent of air.
Cyclone and Anticyclone
A Cyclone is a wind system with a Low pressure at the centre, An anticyclone is wind system with a high pressure at the centre.
Latitude, Longitude, Parallel and Great Circle
″ Latitude is the Angular distance measure North (N) and South (S) of the equator. We can project the line from the point P from the earth surface to the centre of the Earth. ″
- The angle between this line and equator plane is the measure of the latitude of point P.
- Latitude varies from 0° to 90° North or South.
The parallel is a line connecting all points of the same latitude. It is called so because it is parallel to all other lines of Latitude.
0° Parallel – Equator.
90° North – the North Pole.
90° South – the South Pole.
Longitude is the angular distance between meridian passing through a given point and prime meridian
- The Longitude varies from 0° to 180° East or West.
- Meridian is a line joining places with the same longitude.
Any plane that is passed through the centre of sphere bisects that sphere and creates a great circle where it intersects the surface of the sphere.
- A great circle is the largest circle that can be drawn into the sphere and it represents the circumference of the sphere.
- Of all the parallels The Equator alone makes a great circle all other parallel makes the small circle.
- Each meridian makes Semi Great Circle.
- Arc of the great circle joining any part on the equatorial surface is always the shortest route between points.
Circle of Illumination
Sun Illuminates one-half of the earth at any given moment. The edge of the sunlight hemisphere, the circle of illumination, is a great circle, that divides the Earth into the light half and dark half.
Both 23 1/2 ° N and 23 1/2 ° S will receive 90° sunlight and these two tropics represent the farthest limit of the vertical base of the sun
” Tropi” in latin – Tropics, Meaning “Turn”.
This is about the Great Circle if you like this article share or comment below.
Mountains, Plateaus, Plains and its Different Types
In general, geomorphic processes that originate within Earth, called endogenic processes result in an increase in surface relief, while the exogenic processes, those that originate at Earth’s surface, tend to decrease relief. Igneous and tectonic processes constitute the endogenic geomorphic processes.
Exogenic processes consist of various means of rock breakdown, collectively known as weathering, and the removal movement, and relocation of those weathered rock products in the continuum of processes known as erosion, transportation and deposition. These processes decide the landforms on earth.
COMPRESSIONAL TECTONIC FORCES
Compressional Tectonic Forces are divided into two types. They are
- Folding and
Folding, which is a bending or wrinkling of rock layers, occurs when compressional forces are applied to rocks that are ductile (bendable), as opposed to brittle.
- Rocks that lie deep within the crust and that are therefore under high pressure are generally ductile and particularly susceptible to behaving plastically that is, deforming without breaking.
- As a result rocks deep within the crust typically fold rather than break in response to compressional forces.
- As elements of rock structure, unfolds are called anticlines, and downfolds are called synclines.
- The rock layers that form the flanks of anticlinal crests and synclinal troughs are the fold limbs.
- Faulting is the slippage or displacement of rocks along a fracture surface, and the fracture surface along which movement has occurred is a fault.
- When compressional forces cause faulting either one mass of rock is pushed up along a steep-angled fault relative to the other or one mass of rock slides along a shallow, low-angle fault over the other.
- The steep, high-angle fault resulting from compressional forces is termed a reverse fault.
- Where compression pushes rocks along a low-angle fault so that they override rocks on the other side of the fault, the fracture surface is called a thrust fault, and the shallow displacement is an overthrust.
- In both, reverse and thrust faults, one block of crustal rocks is wedged up relative to the other.
- Reverse or thrust faulting can also result from compressional forces that are applied rapidly and in some cases to rocks that have already responded to the force by folding.
- In the latter case, the upper part of a fold breaks, sliding over the lower rock layers along a thrust fault forming an overthrust.
- Together recumbent folds and overthrusts are important to rock structures that have formed in complex mountain ranges such as the Andes, Alps, and the Himalayas.
Types of Mountains
Based on their mode of formation, four main types of mountains can be distinguished.
- Fold Mountains
- Block Mountains
- Volcanic Mountains
- Residual Mountains
- They are caused by large-scale earth movements when stresses are set up in the earth’s crust.
- When such stresses are initiated, the rocks are subjected to compressive forces produce wrinkling or folding along the lines of weakness.
- The unfolded waves are called anticlines and the troughs or downfolds are synclines.
- Due to the complexity of the compression forces, the folds developed much more complicated forms.
- When the crest of a fold is pushed too far, and over fold is formed. If it is pushed still further, it becomes a recumbent fold.
- In extreme cases, fractures may occur in the crust, so that the upper part recumbent fold slides forward over the lower part of a thrust plane, forming an overthrust fold. The over-riding portion of the thrust fold is termed a nappy.
- When the earth’s crust bends folding occurs, but when it cracks, faulting takes place.
- Faulting may be caused by tension or compression, forces which lengthen or shorten the COMPRESSION earth’s crust, causing a section of it to subside or to rise above the RIFT VALLE surrounding level.
- Examples are the Huns Ruck Mountains, the Vosges and Black forest of the Rhineland.
- These are in fact, volcanoes which are built up from material ejected from fissures in the earth’s crust.
- The materials include molten lava, volcanic bombs, cinders, ashes, dust and liquid mud.
- They fall around the vent in successive layers, building up a characteristic volcanic cone.
- Volcanic mountains are often called mountains of accumulation.
These are mountains evolved by denudation. Where the general level of the land has been lowered by the agents of denudation some very resistant areas may remain and these form residual mountains.
Plateaux are elevated uplands with extensive level surfaces and usually descend steeply to the surrounding lowland. They are sometimes referred to as tablelands.
Types of Plateaus
There are three types of Plateaus. They are
- Tectonics Plateaus
- Volcanic Plateaus
- Dissected Plateaus
- These are formed by earth movements which cause uplift, and are normally of a considerable size, and fairly uniform altitude.
- They include continental blocks like the Deccan plateau in India. When plateaux are enclosed by fold mountains, they are known as intermont plateaux.
- Examples are the Tibetan plateau between the Himalayas and the Kunlun, and the Bolivian Plateau between two ranges of the Andes.
- Molten lava may issue from the earth’s crust and spread over its surface to form successive sheets of basaltic lava. These soldify to form a lava plateau.
- Some of the better known volcanic plateaux are the Antrim plateau of Northern Ireland and the north-western part of the Deccan plateau.
- The most remarkable plateau built by lava is the Colombia-snake plateau which covers an area almost twice as big as Malaysia.
- Through the continual process of weathering and erosion by running water, ice and winds, high and extensive plateaux are gradually worn down, and their surfaces made irregular.
- In the humid highlands, stream action and sometimes glaciation cut deep, narrow valleys in the plateaux, which are then described as dissected plateaux.
- An example is the Scottish Highlands. In drier countries, vertical corrosion by rivers and abrasion by winds will dissect the plateau into steep-sided tabular masses termed as mesas and buttes, intersected by deep canyons.
- This is a common feature of arid and semi-arid areas, e.g; in the south-western U.S.A.
A plain is an area of lowland, either level or undulating.
Types of plains
There are three types of plains. They are
- Structural Plains
- Depositional Plains
- Erosion Plains.
- These are the structurally depressed areas of the world that make up some of the most extensive natural lowlands on the earth’s surface.
- They are formed by horizontally bedded rocks, relatively undisturbed by the crustal movements of the earth.
- These are plains formed by the deposition of materials brought by various agents of transportation.
- They are comparatively level but rise gently towards adjacent highlands. Some of the largest depositional plains are due to deposition by large rivers.
- They are called alluvial plains, flood plains and deltaic plains. They form the most productive agricultural plains of the world, intensively tilled and very densely populated.
- The Nile delta of Egypt is noted for rice and cotton cultivation, the Ganges delta for rice and jute growing, while the plain of North China, where the Hwang Ho has spread out a thick mental of alluvium, supports a wide range of crops.
- Glaciers and ice-sheets may deposit a widespread mantle of unsupported fluvial glacial sands and gravels in the out plain or may drop boulder clay, a mixture of various sizes of boulders and clay, to form a till plain or drift plain.
- Outwash plains are usually barren lands, e.g. Some parts of Holland and northern Germany, but boulder clay may be very valuable farming land e.g. the Mid-West of the U.S.A. and East Anglia in England.
- In coastal regions, waves and winds often drive beach materials, mud, sand or shingle, landwards and deposit them on the coastal plain to form marine swamps, mud-flats, tidal and estuarine lowlands.
- Winds may blow Aeolian deposits very fine particles known as loess-from interior deserts or barren surfaces and deposit them upon hills, valleys or plains forming a loess plateau as in north-west China, or loess plains, as in the Pampas of Argentina.
- The loess helps to level an undulating plain by filling up grooves and depressions.
- These plains are carved by the agents of erosions. Such plains of denudation are described as pen plains.
- Mechanical weathering in arid and semi-arid areas wears back the mountains slope to leave a gently sloping pediments or Pedi plains.