THE EARTH'S CRUST
GRANITE ROCKS SIAL- The Oceanic Crust
• Si - silicon and A1 - aluminum.
• High density.
• Iron and calcium are also present.
• Younger part of crust - 200 million years old.
SIMA - The Continental Crust
• Si - silicon and Ma - Magnesium.
• Low density.
• Aluminum, potassium, and sodium.
• Older part of the crust - 3600 million years.
Mantle forms the second layer
• Second layer of the interior of the earth.
• Two sub - layers -1. Upper mantle and 2. Lower mantle.
• Thickness varies between 35km - 2900 km.
• Average density is 4.5 g/cm3
• Upper portion of mantle and crust together known as Lithosphere, lower mantle - Aesthenosphere.
• Third layer of the earth.
• Formed by nickel and iron.
• Also called as Nife
• Nife - Ni - nickel and Fe - ferrous or iron
• Two parts
1. Outer core.
2. Inner core.
• Temperature is 11000° C.
• Inner core is in solid state.
CORE - divided in two layers
1. Inner core
• Molten in stage
• Depth varies from 2900km - 5150 km.
• Density - 10.7 g/cm3.
2. Outer core
• Solid in state
• High temperature
• High pressure
• Depth varies from - 5150 km - 6371 km
• Density - 15 g/cm3
The Classification of Rocks
Rocks are Igneous Rocks, Sedimentary Rocks, Metamorphic Rocks.
• Formed through cooling & solidification of molten material magma (
Erupted from volcanoes, molten material moves towards surface of earth through crack).
• Normally crystalline in structure, do not occur in strata & do not contains fossils.
• Can be subdivided on the basis of mineral composition.
• Basic rocks contain high proportion of basic oxides mainly of iron, aluminium & magnesium
• When they contain high proportion of silica they are said to be Acidic, which are less dense & lighter in color than basic rocks for ex. Granite
• Most igneous rocks are extremely hard & resistant hence are quarried for road making & polished as monuments & grave stones.
• Are parent / primary rocks as all other rocks are derived from it.
• In terms of origin they can be divided into mainly 2 classes viz.
• Formed due to deposition of layers of sediment usually along the water bodies over a long period of time
• Sediment is deposited layer by layer in form of strata hence also known as
• Process of turning sediments into hard rock layers by pressure is known as
• Rocks may be fine grained or coarse, soft or hard & material forming them may be brought by streams, glaciers, winds or even animals.
• May be derived from Igneous, Metamorphic or Sedimentary rocks.
• Hence, Sedimentary rocks are most varied in formation of all rocks.
• They are non-crystalline & often contains fossils of animals, plants & other microorganisms.
• May be classified under 3 categories with respect to their origin & composition viz
Formed when original structure of igneous & sedimentary rocks partially or wholly change under the action of heat & pressure.
• Contains no fossils
• No stratification
• For ex. Clay —> Slate Igneous to Metamorphic Granite —> Gneiss
Mica —» Schist Gabro —> Serpentite Sedimentary to Metamorphic Limestone —> Marble Sandstone —> Quartzite Shale —*■ Schist Coal —» Graphite
Bituminous coal —> Anthracite coal
Types of Mountains
1. Fold Mountains
• Formed by folding of geosyncline sediments under compressible tectonic forces.
• For Ex. Himalaya, Alps, Rockies, Andes, Alapchhian, Ural, Aravalis
• Since the rock strata have been elevated to great heights, Fold Mountains are also called mountains of elevation.
• Are closely associated with volcanic activities.
• Contains many active volcanoes, especially in circum Pacific fold mountain system.
• Are rich in mineral resources such as Tin, Copper, Gold & Petroleum
2. Block Mountains
• Formed due to faults caused by tension or compression forces which lengthen or shorten earth’s crust.
• It causes a section of it to subside or rise above the surrounding level.
• For Ex. Vosges (France), Black Forest (Germany)
• Faulting results in formation of Block Mountains & their counterparts in rift valleys.
• In general, large scale Block Mountains & rift valleys are due to tension rather than compression.
3. Volcanic Mountains
• Also known as mountains of accumulation.
• Formed due to accumulation of thick lava as a result of volcanic eruption.
• Common in circum pacific belt.
• For Ex. Fuji Yama (Japan), Mt. Popa (Myanmar), Mt. Mauna loa (Hawai), Mt. Mayon (Phillipines), Mt. Agung (Bali), Mt. Merapi (Sumatra) & Mt. Catopaxi (Ecuador)
4. Residual / Dissected / Relict Mountains
• Formed due to waning of previously existing elevated regions by erosion.
• For Ex. Nilgiris, Parshavnath, Hills of Peninsula India, Mt. Manodnock
• Mountains evolved by denudation, where the general level of land have been lowered by agents of denudation; also known as mountains of denudation.
Types of Plateaus
• An elevated area compared to its surroundings, having a large almost flat top area (Also known as tableland).
• Like all highlands, Plateaus are also subjected to erosional processes, as a result their original characteristics are highly altered.
• According to their mode of formation & their physical appearance, plateaus may be divided into 3 types viz.
1. Tectonic Plateaus
• Formed by earth movements which causes uplift, of a considerable size with fairly uniform altitude.
• For ex. Deccan plateaus, Mesera plateau (tilted of central Iberia) & Harz plateau (Faulted of Germany).
• When plateaus are surrounded by mountains they are known as intermontane plateaus for ex. Tibetian plateau, Bolivian Plateau.
• When plateaus are surrounded by sea or plains they are known as Continental Plateaus For ex. Deccan plateau, Greenland plateau, South Africa plateau
2. Volcanic Plateau
• Molten lava from the volcanic eruption may solidify to form successive sheets of basalatic lava, known as Lava plateau.
• For ex. Antrim Plateau of Northern island, NW part of Deccan Plateau & Columbia Snake Plateau (Biggest one).
3. Dissect Plateaus
• Formed due to continuous weathering & erosion by running water, wind & ice.
• High plateaus worn down & their surface becomes irregular.
• For Ex. Scottish Highland
• Generally Plateaus have rich mineral resources & have been actively mined for ex.
• African plateau yields gold, diamonds, copper, Manganese & Chromium.
• Brazilian plateau yields iron & Manganese
• Deccan Plateau yields Manganese, Iron & Coal
• Western Australian plateau yields Gold & Iron.
Types of Plains
• Plains usually are the best land of a country & are heavily cultivated & populated.
• Even more at places where rivers transverse the plains.
• For ex: Indo Gangetic Plains, Mississippi Plains & Yang-Tze plain .Some of the most extensive temperate plains are Grasslands like Russian Steppes,
North American Prairies & Argentinian Pampas.
• Plains may be grouped into 3 major types based on their mode of formation viz.
1. Structural Plains
• Structurally depressed areas of the world that makes up some of the most extensive natural lowlands on the earth’s surface.
• Rock layers on the earth’s crust are aligned almost horizontally.
• They are formed by horizontally bedded rocks, relatively undisturbed by the crustal movements of the earth.
• Examples include Russian Platforms, Great plains of USA & Central lowlands of Australia.
2. Depositional Plains
• Plains formed by deposition of materials brought by various agents of transportation.
• Comparatively of equal level but rise gently towards adjacent highlands.
• Depositional work by rivers form extensive alluvial plains, flood plains & deltaic plains; that form most productive agricultural plains of the world.
• For ex. Gangetic plain (for rice & jute), Nile delta of Egypt (for rice & cotton) & Hwang ho plain in China.
3. Glacial Depositional plains
• Glaciers & ice sheets may deposit fluvio glacial sands & gravels in outwash plains.
• May also drop boulder clay (mixture of various sizes of boulders & clay) to form till plain or drift plain.
• Outwash plains are usually barren lands but boulder clay may be very valuable for farming.
4. Aeolian Depositional plains
• Winds may blow Aeolian deposits, very fine particles known as loess, from interior deserts or barren surfaces & deposit them upon hills, valleys or plains forming a loess plateau (ex. in NW China) or a loess plain (Ex. In Pampas of Argentina)
• The loess help in leveling the undulating plain by filling up groves & depressions
• Many of the loess covered plains in the world are fertile agricultural regions.
5. Erosional Plains
• These plains are carved by the agents of erosion (Rain, river, ice, and wind)
• Such plains of denudation are described as Peneplains, which means almost plains.
• In glaciated regions, glaciers & ice sheets scours & levels the land forming ice
• However scooped out by the ice are now filled by the lakes for ex. In Northern Europe & Northern Canada.
• Finland is estimated to have 35000 lakes occupying 10 % of total land surface of the country
• In arid & semi-arid regions, wind erosion lowers the level of the land which are called Reg in Africa.
• Mechanical weathering in arid & semi-arid areas woms mountain slopes leaving a gentle slope, known as Pediplains or Pediments; with remaining steep hills known as Inselbergs.