Geography, Lesson- 2, Class- VII,Question and answers. A. Very short answer type questions:
1. What is the age of the earth?
Answer : The earth is approximately 4.5 billion years old.
2. Into how many layers can the earth be divided?
Answer: The earth can be divided into three main layers : the crust , the mantle and the core.
3. What is the continental crust made of?
Answer: The continental crust is mainly composed of granite and other light silicate minerals. 4. Describe the matle of the earth.
Answer: The mantle is the layer of the earth between the crust and the core and is about 2900 kilometre thick, composed of silicate rocks rich in Magnesium and iron.
5. What is the core made up of?
Answer: The core is made up of iron ( Fe)and Nickel (Ni)with a solid inner core and a liquid outer core.
B. Short answer type questions:
1. Compare the inner and the outer core of the earth.
Answer: The inner core is solid composed mainly of iron and Nickel and is extremely hot.
The outer core is liquid also composed of iron and nickel and generates earth’s magnetic field through its flowing currents.
2. What are rocks and Minerals?
Answer: Rocks are solid aggregates of minerals. Minerals are naturally occurring inorganic substances with a definite chemical composition and crystalline structure.
3. Explain the formation of extrusive igneous rocks.
Answer: Extrusive igneous rocks form when magma riches the earth’s surface and cools quickly, resulting in fine grained textures. Examples include basalt and pumice.
4. Describe the formation of sedimentary rocks
Answer: Sedimentary rocks formed from sediments at the surface of the earth, either in water or on land. They are also called stratified rocks as deposition takes place in layers.
5. Write three uses of rocks and Minerals.
Answer: Rocks and Minerals are used in construction (granite for buildings) in manufacturing (limestone for cement) and in technology (silicon in electronics)
C. Long answer type questionsย :ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย 1. The the structure of the earth is divided into concentric layers.Explain with the help of a diagram.ย ย ย ย ย ย ย ย ย ย ย ย
Answer: The earth is composed of three main concentric layers: the crust (outermost layer) the mental (middle layer) and the core (innermost layer) divided into a solid inner Core.
2. What is meant by The crust? Highlight the difference between the continental crust and Oceanic crust.
Answer: The crust is the Earth’s outermost layer. The continental crust is thicker,less dense,and composed mainly of granite. The oceanic crust is thinner, denser, and composed mainly of basalt
3. Trace the formation of metamorphic rocks.
Answer: Metamorphic rocks form from the alteration of existing rocks due to high temperature,pressure, and chemically active fluids.This process called metamorphism, changes the mineral composition and texture of the rocks (e.g limestone transforms into marble).
4.What is a Rock cycle? Explain the process of formation of rocks with the help of a diagram.
Answer: The Rock cycle is the continuous process of transformation of rocks from one type to another. Igneous rocks can breakdown into sediments and form sedimentary rocks, which can then be buried and transformed into metamorphic rocks. This can melt into Megma, which upon cooling, forms igneous rocks again.
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