Give long note for the following
•Changing Earth
•In side the Earth
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Answers
Answer:
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Explanation:
re sand dunes?
(vi) How are beaches formed?
(vii) What are ox-bow lakes?
Answer: (i) The plates move because of the movement of the molten magma inside the earth.
(ii) Exogenic forces. The forces that work on the surface of the earth are called as exogenic forces.
Endogenic forces. The forces that act in the interior of the earth are called as endogenic forces.
(iii) Erosion is the wearing away of the landscape by different agents like water, wind and ice.
(iv) During floods, layers of fine soil and other material called sediments are deposited on the river bank. This leads to the formation of a flat fertile flood plains.
(v) Sand dunes are low hill-like structures formed by the deposition of sand in the deserts.
(vi) Beaches are formed when the sea waves deposit sediments along the shores of the sea.
(vii) When the meander loop is cut off from the main river, it forms a cut-off lake. As its shape is like an ox bow, it is also known as ox-bow lake.
Question 2. Tick the correct answer:
(i) Which is not an erosional feature of sea waves?
(a) Cliff
(b) Beach
(c) Sea cave.
(ii) The depositional feature of a glacier is
(a) Flood plain
(b) Beach
(c) Moraine.
(iii) Which is caused by the sudden movements of the Earth ?
(a) Volcano
(b) Folding
(c) Flood plain.
(iv) Mushroom rocks are found In
(a) Deserts
(b) River valleys
(c) Glaciers.
(v) Ox bow lakes are found In
(a) Glaciers
(b) River valleys
(c) Deserts.
Answer: (i) – (a), (ii) – (c), (iii)-(a) , (iv) -(a), (v)-(b)
ncert-solutions-for-class-7-geography-social-science-chapter-3-our-changing-earth-3
The Changing Earth
Erosion is the transportation of weathered pieces of bedrock through the agents of wind, water (rivers and ice), and gravity. As mountains are built up by tectonic forces, they are also broken down and carried away by weathering and erosion.
The pull of Gravity makes surface material move downward. Downslope movements may be rapid or very slow. They may involve only the surface material, or they may involve the bedrock underneath. Houses built on hills can contribute to soil movements because the weight of the homes may add to the gravitational force. Wind contributes to the erosional process by carrying surface material from one location to another. Glaciers, huge sheets of ice that can move slowly over land, pick up and carry rocks and soil with them. When they pass through river valleys, the glaciers deepen those valleys. Mountain Glaciers, coupled with the downward force of gravity, create avalanches that can cause great erosional damage.
Of all the erosional agents, running water is the most powerful. Rivers, working with the force of gravity, have devastating erosional impact. The action of rivers flowing against the land has formed gorges as large as the Grand Canyon. As rivers erode land, they carry deposits with them. DELTAS are formed at the mouths of rivers that empty into a lake or an ocean. The soil that is carried along a river and deposited as its mouth is the richiest and most fertile of all soils. The Nile and the Mississippi Rivers have formed deltas that are noted for their rich soil, making these regions highly desirable for agriculture.
Despite these limitations, we know that the centre of the Earth is very hot. We only have to drill a small way to observe temperature rises of some 25°C per kilometre, so at some point, everything might be so hot that we would strike molten rock like the lava that flows from volcanoes.
However, common sense tells us that this rapid rise in temperature we see from surface drilling could not continue indefinitely or the centre of the Earth would be hotter than the Sun.
The currently accepted theory of the Earth’s structure is that it has a core (a solid inner core and a liquid outer core), a viscous mantle (divided into an upper mantle and mantle) and a silicate crust.
We believe that gravitational attraction and melting has nicely sorted the composition of the Earth so that dense materials have been pulled to the core, leaving lighter elements on the surface to form the crust.
The core
Recording the amount of time it takes refracted and reflected seismic waves generated by earthquakes to travel through different layers of the Earth has told us a lot about the type and location of things below the crust. For example, S-waves cannot pass through the Earth’s core at all, while the changes in seismic velocity between layers cause some waves to refract (bend like light passing between two media, such as air and water) and other waves to reflect like light from a mirror.
Based on studies of dense meteorites (parts of other planets), we can reasonably assume that the Earth’s solid core is composed mainly of iron (around 80%), with small amounts of nickel. The liquid outer core is composed of iron mixed with nickel and trace amounts of lighter elements. At present, we believe that convection in the liquid outer core combined with the rotation of the Earth causes the Earth’s magnetic field.
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