Std 7
Sub- Social Science
Chapter-10 Earth's internal composition and landforms
Workbook Answers
1) On which planet of the solar system is a developed life found?
Developed life is found on the planet Earth.
2) How are the layers of the earth arranged?
The layers of the earth are arranged as the crust, mantle, and core.
3) What is called a ‘crust’? How is it?
The crust is the outermost layer of the Earth. It is solid and thin compared to other layers.
4) SiAl is mainly composed of which minerals?
SiAl is mainly composed of silica and aluminium.
5) Why is the core of the earth called ‘NiFe’?
The core is called ‘NiFe’ because it is mainly composed of nickel (Ni) and iron (Fe).
6) How many are the main types of rock? Which are they?
There are three main types of rocks: igneous, sedimentary, and metamorphic.
7) What is meant by a rock cycle?
The rock cycle is the continuous process of transformation of rocks from one type to another.
8) Which minerals are used as fuel?
Coal, petroleum, and natural gas are minerals used as fuel.
9) Which two natural disasters occur due to the sudden movements in the earth’s crust?
Earthquakes and volcanic eruptions occur due to sudden movements in the earth’s crust.
10) What is an earthquake?
An earthquake is the shaking of the Earth's surface caused by sudden movements in the Earth's crust.
11) What is called a focus of an earthquake?
The focus is the point inside the Earth where an earthquake originates.
12) How do the local people predict the possibilities of an earthquake?
Local people predict earthquakes by observing unusual animal behavior, underground water changes, and minor tremors.
13) Which factors bring changes on the surface of the earth?
Factors like wind, water, ice, and tectonic activity bring changes on the Earth’s surface.
14) Define erosion.
Erosion is the process of wearing away of the Earth's surface by natural agents like wind, water, and ice.
15) What is called an 'Ox-bow lake'?
An ox-bow lake is a crescent-shaped lake formed when a river meander is cut off from the main flow.
16) What is called a natural levee?
A natural levee is a raised bank formed along a river due to the deposition of sediments during floods.
17) What is called a stack?
A stack is a vertical column of rock formed by wave erosion along a coast.
18) What is called a sea cliff?
A sea cliff is a steep rock face or slope formed along the coastline due to the constant action of sea waves eroding the land.
6. Answer the following questions briefly:
1) What is called an igneous rock? State its types.
Igneous rocks are formed by the cooling and solidification of molten magma.
There are two types of igneous rocks: intrusive (plutonic) and extrusive (volcanic).
2) What is meant by an intrusive igneous rock?
Intrusive igneous rocks are formed when magma cools and solidifies beneath the Earth's surface. They have large crystals.
3) What is meant by Endogenic (internal) force?
Endogenic forces are internal forces that originate inside the Earth and cause movements like earthquakes, volcanic eruptions, and mountain formation.
4) Which rocks are known as the extrusive igneous rocks?
Extrusive igneous rocks are formed when lava cools and solidifies on the Earth's surface.
Example: Basalt.
5) What is a waterfall?
A waterfall is a natural feature where water flows over a steep vertical drop or cliff, usually in the course of a river.
7. Answer the following questions:
1) Explain metamorphic rocks with examples.
Metamorphic rocks are formed when existing rocks are subjected to great heat and pressure, causing physical or chemical changes.
Examples:
Slate (formed from shale)
2) What is meant by a rock cycle? Explain.
The rock cycle is a continuous process in which rocks changes to another type under certain conditions in a cyclic manner. This process of transformation of rock is called Rock-cycle.
For example, igneous rocks can break down into sediments and form sedimentary rocks, which can turn into metamorphic rocks under heat and pressure, and may melt to become magma and form igneous rocks again.
8. Write a Short Note:
1) SiAl and SiMa:
SiAl stands for Silica (Si) and Aluminium (Al). It is there for called siAl. It forms the continental crust and is lighter and found mostly in the upper layer of the Earth.
SiMa stands for Silica (Si) and Magnesium (Ma). It is there for called siMa. It forms the oceanic crust and is denser, lying beneath the SiMa layer.
2) Formation of a volcanic mountain:
A volcanic mountain is formed when magma from beneath the Earth’s crust escapes through a vent.
1. Magma Formation: Deep inside the Earth, due to high temperature and pressure, rocks melt and form magma. This molten rock collects in a magma chamber beneath the Earth's surface. 2. Pressure Build-Up: Over time, pressure builds up in the magma chamber. Gases mixed with the magma increase the pressure further.
3. Eruption: When the pressure becomes too great, magma forces its way upward through cracks or vents in the Earth’s crust. It erupts as lava, ash, and gases
4. Lava Cooling: The lava that erupts cools and solidifies on the surface. Repeated eruptions cause layer upon layer of hardened lava and ash to build up. 5. Mountain Formation: Gradually, these layers accumulate and form a volcanic mountain.
