1 Summary Geography Class 09 ## Last class revision (5:09 PM) ## Interior of the earth (5:20 PM) - ***The diagrammatic representation of the interior of the earth:*** - ![](https://www.edrawsoft.com/templates/images/earth-structure.png) - ***The chemical divisions of the earth's interior:*** - The 3 layers of crust, mantle, and core are the chemical division of the earth. - ***Crust:*** - It is the uppermost layer of the earth. - It is made up of light elements such as silica, aluminium, magnesium, etc. - It is the lightest in terms of density. - It is of 2 types, continental crust, and oceanic crust. - ***The difference between the continental crust and oceanic crust:*** - | | | | --- | --- | | **Continental crust:** | **Oceanic crust:** | | Very thick(35-45 km) | Very thin(8-10 km) | | Lighter in density. | Heavier in density. | | Rocks of brighter colour. | Rocks of darker colour. | | Rocks are older | Rocks are younger | | It is richer in Alumium, sodium, and Potassium elements(SiAl layer) | It is richer in Magnesium, calcium, and Iron. (SiMa layer) | - ***Mantle:*** - It is lighter than the core and denser than the crust. - It accounts for 83% volume of the earth. - It consists of 68% of the mass of the earth. - The overall depth of the mantle extends to 2888 km. - The mantle contains a higher proportion of magnesium and a lower proportion of silica and aluminium. - It is divided into the upper and lower mantle. - ***Core:*** - It is the innermost and densest layer of the earth. - It is rich in nickel and iron therefore it is also called as NiFe layer. - It is divided into the inner core and outer core. - The inner core is solid and the outer core is liquid as the pressure at the inner core is very high. ## Physical division - ***Lithosphere:*** - It is a solid layer made up of Crust and the upper part of the Upper Mantle. - It is a hard and rigid outer layer that is divided into different plates. - The thickness of the lithosphere is nearly 100 Km. - ***Asthenosphere:*** - It extends between 100-400 km. - It is in a semi-solid and semi-liquid state and undergoes deformation under pressure. - It is also a source of magma on the surface. - It is also called a low-velocity zone due to the slowing down of earthquake waves in this zone. - ***Mesosphere*** - It includes the rest of the Mantle. - ***Barrysphere:*** - It includes both the outer and inner core. ## Composition of the earth (6:17 PM) - ***Elements of the entire earth:*** - Iron: 35% - oxygen: 30% - Silicon- 15% - Magnesium: 13% - ***Major Elements of the Earth's Crust:*** - Oxygen: 46.60% - Silicon: 27.72% - Aluminium: 8.13% - Iron: 5%. ## Discontinuities in the interior of the earth (6:21 PM) - It is the transition zone between the different layers of the earth's interior with different physical and chemical characteristics. - ***Diagramatic representation of discontinuities:*** - ![](https://hi-static.z-dn.net/files/dbc/73bbb3b7c98f2c6922076292c9bb3fd9.jpg) - There are mainly 5 types of discontinuities: - ***Conrad Discontinuity:*** - It is Within the Crust (Upper and Lower Crust). - ***Mohorovicic or Moho Discontinuity:*** - It is Between Crust and the Mantle. - ***Repetti Discontinuity*:** - It is Between the Upper and the Lower Mantle. - ***Guttenberg Discontinuity:*** - It is Between Mantle and Outer Core. - ***Lehmann Discontinuity:*** - It is Between the Outer and Inner Core. ## Types of rocks (6:32 PM): - Any naturally occurring aggregate of minerals is called a rock. - ***Difference Between Rocks and Minerals:*** - | | | | --- | --- | | **Rocks:** | **Minerals:** | | Rocks are an aggregate of mineral elements. | Minerals are solid inorganic substances occurring naturally. | | A rock has no definite chemical composition | Minerals have a definite chemical composition. | | Minerals are organized to form rocks. | Elements are organized to form compounds that are known as minerals. An element is a pure substance. | | The three chief types of rocks are- Igneous, Sedimentary, and metamorphic. | Four chief mineral groups are- Silicates, Carbonates, Sulphides, and metallic minerals. | | Basalt, Granite, Sandstone, Slate, and Quartz are some important types of rocks. | Iron, Silicon, Magnesium, Nickel, and Calcium, are abundant minerals of the earth. | ## Types of rocks (7:02 PM) ## Igneous rocks: - They are formed due to the cooling, solidification, and crystallization of molten material from the earth's interior. - They are also called primary rocks. - Igneous rocks are of two types, intrusive and extrusive igneous rocks. - ***Intrusive igneous rocks:*** - They are formed from the cooling of magma inside the earth. - The slow cooling of magma results in a crystalline texture with higher strength. - They are also called Plutonic rocks. - Examples are granite, Gabbro, etc. - ***Extrusive igneous rocks:*** - They are formed due to the cooling of magma above the earth's surface. - Faster cooling results glassy texture but with lower strength. - They are also called Volcanic rocks. - Examples are  Basalt, Andesite, etc. - Igneous rocks are also be classified as: - ***Acidic or Silsic:*** - Where the silica percentage is more than 66%. - For example Granite. - ***Basic or Mafic:*** - Where the silica percentage is less than 52%. - For example Basalt. ## Sedimentary rock (7:29 PM) - These are the secondary rocks formed by the solidification of sediments of original igneous or metamorphic rocks or another sedimentary rock. - ***Stages in the formation of sedimentary rock:*** - Weathering>>Transportation(by a different agent such as wind, water, glacier, etc)>>Deposition(in a basin)>>Lithification( conversion of loose sediments into hard rock)>>Compaction(sediments are squeezed by the weight of overlying layers)>>Cementation(It involves binding together of compacted sediments by natural cementing material such as silt). - Sedimentary rocks are formed in different layers or strata. - They contain fossil evidence. - Examples of sedimentary rocks are Sandstone, Limestone, Shale, Clay, Chalk, Coal, and Gypsum. ## Metamorphic rock (7:47 PM) - Metamorphism involves changes in the form of rocks through physical or chemical processes. - The change in pressure conditions results in dynamic metamorphism and the change in temperature results in thermal metamorphism, together it causes thermo-dynamic metamorphism. - During the process of Metamorphism if the minerals are arranged in a series of bands along a plain it is called foliation. - foliation involves banding. - When minerals are arranged linearly it is called Lineation. - ***Examples of Metamorphics rocks:*** - Granite resulting in Gneiss. - Limestone resulting in Marble. - Sandstone resulting in Quartize. - Shale resulting in Schist. - Clay resulting in Slate. - Coal results in Graphite and Diamonds. ## The Rock Cycle (8:01 PM) - ***The diagrammatic representation of the Rock cycle:*** - ![](https://opentextbc.ca/physicalgeology2ed/wp-content/uploads/sites/298/2019/06/rock-cycle-3.gif) - In nature, all the rocks get converted into each other form. - The outcrop is the elevated part of the surface thus it undergoes weathering very easily. ## The topic for the next class: Earth's Movements.