GEOGRAPHY QUIZ (Also available in the book- "Ordinary Level Physical Geography F3 & 4") THE EARTH STRUCTURE 1. Define the earth Answer The earth is a system which is composed of outer and inner zones which include the atmosphere, the hydrosphere, the biosphere and the crust, mantle and the core respectively. 2. Identify concentric zones of the earth Answer The concentric layers (zones) of the earth include the crust, mantles and the core. The crust: the outermost and the thinnest zones in the interior of the earth. It is largely composed of igneous rocks. The crust consists of two layers that are sial and sima. Sial is the outermost layer, which forms the continents and is made of granitic rocks with a density of about 2.65gms/cc to 2.70gms/cc. Sima is beneath sial. It has denser rocks than those in sial. Sima forms the ocean floor. The mantle: the layer that lies beneath the crust. It is separated from the crust by zone called mohorovicic discontinuity or Moho. It consists of pale green minerals called Olivine (ferromagnesium silicates) in the form of ultra basic rock. Mantle is divided into two parts, that is, upper mantle and the lower mantle. The upper mantle is rigid and combines with the crust to form a large layer called lithosphere. Below the upper solid mantle there is a layer called asthenosphere. It has less rigid and more plastic (semi-molten) material, which can move easily. The core: also called barysphere or centrosphere. It is separated from the mantle by zone of separation called Gutenberg discontinuity. The core is divided into two parts that are the outer core and the inner core. The outer core is liquid in nature due to high temperature of up to 3700oC and consists of nickel and iron (NIFE). Inner core is thought to be solid because of high pressure at the center and is composed mainly of iron. The temperature at the center is about 5500oC. 3. What is the name given to the outer layer of the earth? Answer The name given to the outer layer of the earth is the crust. 4. Where is asthenosphere found? Answer Asthenosphere is found below the upper solid mantle 5. Draw the diagram that illustrates the internal structure of the earth. Answer 6. What are the mineral constituents of sial and sima? Answer Sial is made of granitic rocks while Sima consists of silica but in less proportion than in the sial and minerals rich in magnesium and iron. 7. Explain five characteristics of each of the following: the crust, the mantle and the core Answer The crust • The outermost and the thinnest of the zones in the interior of the earth. • It is between 8 – 50 km (5 – 30 miles) thick. • It is largely composed of igneous rocks. Other types of rocks also exist as a result of changes on earth’s surface; • The rocks of the crust are crystalline, hard and brittle. • The crust consists of two layers that are sial and sima. The mantle • This layer is beneath the crust. • It is separated from the crust by zone called mohorovicic discontinuity or Moho. • It extends downwards to about 2900 km (1800 miles) where the temperatures may reach about 5000oC. • The rocks are denser to about 3.03 - 3.3gms/cc. • There is high temperature which generates convection currents. • It consists of pale green minerals called olivine (ferromagnesium silicates) in the form of ultra basic rock. • Mantle is divided into two parts that is upper mantle and the lower mantle. • The upper mantle is rigid and combines with the crust to form a large layer called lithosphere. • Below the upper solid mantle there is a layer called asthenosphere. The core • It is separated from the mantle by zone of separation called Gutenberg discontinuity. • It has a diameter of about 6900 km (4300 miles). • It is under high pressure with the average density of about 12 gms/cc. • It is divided into two parts that are the outer core and the inner core. • It is in a molten state due to great heat and pressure • It is comprised of uranium, rhodium and thrombium in its outer part 8. Mention the zone that separates the crust (lithosphere) from the mantle (mesosphere). Answer The zone that separates the crust (lithosphere) from the mantle (mesosphere) is called Mohorovicic discontinuity or Moho. 9. Mention the zone that separates the mantle (mesosphere) from the core (barysphere). Answer The zone that separates the mantle (mesosphere) from the core (barysphere) is called Gutenberg discontinuity. 10. Differentiate between (a) Sial and Sima (b) Inner and Outer core Answer (a) Sial and Sima Sial is the outermost layer which forms the continents and is made of granitic rocks with a density of about 2.65gms/cc to 2.70gms/cc. Since these rocks contain a large proportion of silica and aluminium they are collectively called SIAL. Sima is a layer beneath sial. It has denser rocks than those in sial, consists of silica but in less proportion than in the sial and of minerals rich in magnesium and iron. It has the density of about 2.9gms/cc. Sima forms the ocean floor. (b) Outer and Inner core The outer core is liquid in nature due to high temperature of up to 3700oC and consists of nickel and iron (NIFE). It is estimated to be 2100 km with a density of about 10.5 gms/cc. Inner core is thought to be solid because of high pressure at the center and is composed mainly of iron. Its density is about 16-17 gms/cc with a diameter of about 2600 – 2700 km (1600 -1700 miles). 11. Define rocks. Answer Rocks are aggregates of minerals in a solid state. It includes substances like clay, shells, sandstones and corals. Rocks, which contain metallic compounds, are called ores. For example those which contain iron are called iron ores. 12. Give the distinction between the following terms: (a) Thermal and dynamic metamorphism. (b) Regional and local metamorphism Answer (a) Thermal (contact) metamorphism is caused by intense heat. This can take place when the rock comes into contact with the hot molten material like magma or lava. The rock can change its appearance and character. Dynamic metamorphism is influenced by pressure. The pressure is caused by compressional forces which cause earth movement and bring about mountain formation. (b) Regional metamorphism is the one, which affects a large area, an example is dynamic metamorphism. Local metamorphism is the one, which affects a small area; an example is thermal (contact) metamorphism. 13. Classify rocks according to their mode of formation Answer According to the mode of formation, rocks are classified as igneous, sedimentary and metamorphic. Igneous Rocks: These are formed by the cooling and solidification of the molten material from the interior of the earth. When the molten materials are still in the earth’s crust are referred as magma and when they reach the surface of the earth are called lava. Sedimentary Rocks: These are the rocks formed by the process of sedimentation. That is deposition or accumulation and lithification of sediments of some weathered particles and other materials. The particles or sediments are deposited by water, wind or moving ice. After a long period of time the materials become compacted or lithified. The materials are deposited in layers (strata) to form a sedimentary rock. Metamorphic Rocks: These are the rocks which are formed when one type of rock changes into another type of rock after having been subjected under intense heat or pressure or both. Any rock can change to form metamorphic rock. 14. What is geological time scale? Answers Geological time scale is a scheme or chart that indicates age, classification of rocks and the associated geo-morphological and biological events. The chart accounts for the geological time extending as far back about 600 million years ago. The period before 600million years ago (before Paleozoic era) has generally been referred to as the Pre-Cambrian era. But there is scanty evidence for the classification of this vast time span. 15. What is the importance of the Geological Time Scale? Answer (a) It depicts the ages of the rocks by showing the time when certain types of rock were formed and how they were formed. For example, some were formed by glacial deposition while others were formed by volcanic eruption. (b) It helps in understanding when and how different landforms were formed. (c) By studying keenly the geological time, one can be able to predict the occurrence of crustal deformations likely to take place. (d) The geological time scale records the life for plants and animals. This life record helps in understanding the relationship existing between living things and the geological processes. For example, the chart shows that plants, Plants emerged when the soil had developed and animals came into existence when plants already existed to provide food. 16. Mention the values of rocks to human life. Answer (a) Rocks are important in the formation of soil, which can be good for agriculture. (b) Storing underground water. Water is stored in the water holding stratum and can come out as spring where the water holding stratum has outcropped or is near the surface. (c) Some rocks are used for fuel like coal and mineral oil. (d) Rocks are also used for building. A wide range of rocks like limestone, sandstone, etc. are used for building houses and road construction. (e) Limestone is also used for manufacturing of cement. (f) Salt extraction; various salts are obtained from rocks occurring in some places. For example, in Tunisia and Morocco there are large deposits of salt. (g) Manufacturing of chemicals: Some rocks have salts such as nitrates or phosphates while others have potash. These salts are used for making dyes, fertilizers and medicines. Gypsum is used for making Plaster of Paris (PoP) and silica sand used for making glass. (h) Mineral deposits; Mineral ores occur in veins of some rocks such as igneous rocks. The ores were formed when magma cooled. Valuable minerals extracted from rocks include gold, lead, copper, tin, silver, zinc, aluminium, calcium and manganese. (i) Some rocks are so impressive such that they attract some tourists to come and view them. In doing so the country gets foreign currency. Such attractive rocks include coral reefs and granitic tors. (j) Marble is used in decorating floors of some important buildings such as banks, etc.
Posted on: Sat, 21 Sep 2013 09:11:43 +0000
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