Samacheer Kalvi Class 8 Social Science Solutions Chapter 1 Rocks and Soil

material Climate Topography Organisms Time Processes Soil
properties

Rocks	Mode of formation	Characteristics	Examples	Uses
Igneous	Solidification of molten magma	Hard, impermeable	Basalt, Granite	Construction works
Sedimentary	Sediments deposited by various agents	Non-crystalline rocks, soft and easily eroded	Chalk, Limestone, Rock salt	Build stone, make plaster and cement
Metamorphic	Altered by high temperature and pressure of igneous and sedimentary rocks.	Crystalline, alternate bands of light and dark minerals.	Anthracite, Marble, Slate, Gneiss.	Building materials, artwork.

In simple words: This table shows how different types of rocks are made, what they are like, some examples, and what we use them for. Each rock type has unique features.

🎯 Exam Tip: When completing such tables, ensure the information for each rock type is consistent across all columns, linking its formation, characteristics, examples, and uses.

 

XII. Additional Important Questions - Choose the Correct Answer:

 

Question 1. Petrology is derived from the ................... word.
(a) English
(b) Latin
(c) Greek
(d) French
Answer: (c) Greek
In simple words: The word 'petrology', which is the study of rocks, comes from ancient Greek words. 'Petrus' means rock and 'logos' means study.

🎯 Exam Tip: Knowing the etymology (origin) of scientific terms can sometimes help in remembering their meaning and context.

 

Question 2. The soils found in the desert regions are ...................
(a) Mountain Soils
(b) Desert Soils
(c) Black Soil
(d) Red Soil
Answer: (b) Desert Soils
In simple words: The type of soil found in very dry desert areas is called desert soil. This soil is usually sandy and not very good for growing plants.

🎯 Exam Tip: Connect the environment or geographical region directly to the specific type of soil found there.

 

Question 4. is a part composed of organic matter mixed with mineral matter.
(a) Humus
(b) Top Soil
(c) Elevated layer
(d) Sub-soil
Answer: (b) Top Soil
In simple words: Topsoil is the part of the ground that has both organic stuff like dead leaves and small bits of rock. It is very important for growing plants.

🎯 Exam Tip: Remember that topsoil is crucial for plant growth because it contains the most organic matter and nutrients.

 

Question 5. The time to form one cm of soil is
(a) 100 years
(b) 200 years
(c) 500 years
(d) 1000 years
Answer: (b) 200 years
In simple words: It takes a very long time, around 200 years, for just one centimeter of soil to form naturally. This shows how precious soil is.

🎯 Exam Tip: Highlight the extremely slow rate of soil formation to emphasize its importance for conservation efforts.

 

Question 6. is known as the zone of accumulation.
(a) Humus
(b) Top Soil
(c) Elevated layer
(d) Sub-soil
Answer: (d) Sub-soil
In simple words: The sub-soil is the layer where materials like clay and minerals from above often gather and build up.

🎯 Exam Tip: Understand the different soil horizons (O, A, B, C, R) and what processes occur in each layer, especially accumulation in the B-horizon (sub-soil).

 

Question 7. In the soil composition are minerals.
(a) 5%
(b) 10%
(c) 25%
(d) 45%
Answer: (d) 45%
In simple words: Almost half of what soil is made of comes from small pieces of minerals.

🎯 Exam Tip: Memorize the approximate percentages of the main components of ideal soil: minerals, organic matter, water, and air.

 

Question 8. In the soil composition is air.
(a) 5%
(b) 10%
(c) 25%
(d) 40%.
Answer: (c) 25%
In simple words: About a quarter of the space in soil is filled with air. This air is important for plants and small creatures in the soil.

🎯 Exam Tip: Remember that air and water typically each make up about 25% of ideal soil, allowing for root respiration and nutrient transport.

 

Question 9. soils are formed by the deposition of silt by the running water.
(a) Black
(b) Red
(c) Alluvial
(d) Desert
Answer: (c) Alluvial
In simple words: Alluvial soils are created when rivers carry fine particles called silt and drop them off in new places. These soils are often found near rivers and are very fertile.

🎯 Exam Tip: Associate alluvial soils directly with river systems and floodplains, as their formation is intrinsically linked to water deposition.

 

Question 10. the Soil composition is organic matter.
(a) 5%
(b) 10%
(c) 25%
(d) 45%
Answer: (a) 5%
In simple words: Only a small part, about 5%, of soil is made from organic matter, like decayed plants and animals. This small part is very important for soil health.

🎯 Exam Tip: Note that organic matter, despite being a small percentage, plays a huge role in soil fertility, water retention, and overall structure.

 

II. Fill in the blanks.

 

Question 1. A rock is an aggregate of or more minerals.
Answer: A rock is an aggregate of one or more minerals. Rocks are naturally occurring solid masses made up of one or more minerals, which are naturally occurring solid chemical substances. Rocks are the basic building blocks of the Earth's crust.
In simple words: Rocks are usually made of one or more types of minerals stuck together.

🎯 Exam Tip: Understand that a rock is typically a mixture of minerals, while a mineral is a single, naturally occurring chemical compound with a specific crystal structure.

 

Question 2. There are different types of minerals found on the earth Surface.
Answer: There are about 2000 different types of minerals found on the Earth's surface. Each mineral has unique chemical and physical properties. These vast numbers reflect the complex geological processes that have shaped our planet.
In simple words: The Earth's surface has about 2000 kinds of minerals.

🎯 Exam Tip: While knowing the exact number isn't crucial, remember that there are thousands of distinct mineral types, showcasing Earth's geological diversity.

 

Question 3. Rocks are classified in to types.
Answer: Rocks are classified into three main types. These classifications are based on how the rocks are formed. The three types are igneous, sedimentary, and metamorphic rocks, each with distinct formation processes.
In simple words: Rocks are put into three main groups based on how they were made.

🎯 Exam Tip: Always remember the three fundamental rock types: igneous, sedimentary, and metamorphic, as they form the basis of the rock cycle.

 

Question 4. The two types of Intrusive Igneous rocks are
Answer: The two types of intrusive igneous rocks are Plutonic rocks and Hypabysal rocks. Intrusive igneous rocks form when magma cools and solidifies beneath the Earth's surface, and these two categories describe their depth of formation.
In simple words: Igneous rocks that form inside the Earth are called Plutonic and Hypabysal rocks.

🎯 Exam Tip: Distinguish intrusive (cools inside Earth) from extrusive (cools on surface) igneous rocks, and then remember the specific names for intrusive types.

 

Question 5. Igneous Rocks are rocks
Answer: Igneous rocks are also known as primary rocks. They are called primary because they are formed directly from the cooling and solidification of molten rock (magma or lava), making them the original rocks from which other rock types can be derived.
In simple words: Igneous rocks are the first type of rocks formed, so they are called primary rocks.

🎯 Exam Tip: Recognize "primary rocks" as a synonym for igneous rocks due to their foundational role in the rock cycle.

 

Question 6. into slate caused by thermal metamorphism.
Answer: Shale changes into slate through thermal metamorphism. When shale, a sedimentary rock, is exposed to high temperatures and pressure, it transforms into the metamorphic rock called slate. Basalt is mentioned in the question, but the transformation from shale to slate is the more common example for thermal metamorphism leading to slate.
In simple words: When shale rock gets very hot, it changes into slate through a process called thermal metamorphism.

🎯 Exam Tip: Learn common parent-daughter rock transformations in metamorphism, such as shale to slate, sandstone to quartzite, and limestone to marble.

 

Question 7. Soil is a basic requirement for the growth of and
Answer: Soil is a basic requirement for the growth of plants and animals. Plants need soil to grow and get nutrients, and many animals live in or depend on soil for food and shelter. Soil supports the entire food web.
In simple words: Plants and animals need soil to grow and live.

🎯 Exam Tip: Emphasize soil's fundamental role as the foundation for most terrestrial life and ecosystems.

 

Question 8. To become a well-matured soil, it takes about years.
Answer: It takes about 3000 years for soil to become well-matured. Soil formation is a very slow process, influenced by climate, parent material, topography, organisms, and time. This long period highlights the importance of protecting existing soil.
In simple words: Soil takes a very long time, around 3000 years, to fully develop and become mature.

🎯 Exam Tip: Remember this specific time frame to illustrate the slow, non-renewable nature of mature soil, underscoring the need for soil conservation.

 

Question 9. Parent Rock is converted to loose Rock by
Answer: Parent rock is converted to loose rock by the process of weathering (which is the first step in soil formation). Weathering breaks down larger rocks into smaller fragments through physical, chemical, and biological processes. This loose material then combines with organic matter to form soil.
In simple words: Over time, the main rock breaks down into loose rock because of weathering, which then helps make soil.

🎯 Exam Tip: Connect the breakdown of parent rock directly to weathering, recognizing it as the initial and crucial stage in the complex process of soil formation.

 

Question 10. Laterite soil is suitable for plantation crops like
Answer: Laterite soil is suitable for plantation crops like tea and coffee. These soils are typically found in tropical regions that experience alternating wet and dry seasons, and they are well-suited for crops that thrive in acidic conditions and require good drainage.
In simple words: Tea and coffee plants grow well in laterite soil because it has the right conditions for them.

🎯 Exam Tip: Remember that laterite soils are often infertile for traditional agriculture but are excellent for specific plantation crops, especially tea and coffee.

 

III. State whether the following statements are true or false:

 

Question 1. To become a well-matured soil, it taken about 2000 years.
Answer: False
This statement is false. It actually takes about 3000 years for soil to become well-matured. The process is lengthy and depends on many environmental factors.
In simple words: It takes longer than 2000 years, closer to 3000 years, for soil to grow fully mature, so this statement is wrong.

🎯 Exam Tip: Be precise with numerical facts like timeframes for geological processes; a slight difference can make a statement false.

 

Question 2. Lava comes out from a volcano.
Answer: True
This statement is true. Lava is molten rock that flows out from a volcano during an eruption. Once it reaches the Earth's surface, it cools and solidifies to form extrusive igneous rocks.
In simple words: When a volcano erupts, hot melted rock called lava comes out, so this is correct.

🎯 Exam Tip: Clearly differentiate between magma (molten rock beneath the surface) and lava (molten rock on the surface).

 

Question 3. The word Ignis means rock.
Answer: False
This statement is false. The word "Ignis" means fire in Latin. Igneous rocks are named this way because they are formed from intense heat, like fire, through the cooling of molten rock.
In simple words: The word "Ignis" means 'fire', not 'rock'. So, this statement is wrong.

🎯 Exam Tip: Understanding the etymology of geological terms (like igneous from Latin 'ignis') can help you remember their definitions and characteristics.

 

Question 4. Oldest Sedimentary rocks of the world has been identified in Green land.
Answer: True
This statement is true. Some of the oldest known sedimentary rocks have been discovered in Greenland. These ancient rocks provide valuable clues about Earth's early history and the conditions that existed billions of years ago.
In simple words: The oldest sedimentary rocks on Earth were indeed found in Greenland, making this statement true.

🎯 Exam Tip: Note key locations associated with significant geological discoveries, as these can be factual points in questions.

 

Question 5. Soil supports ecosystem and play an important role in land management.
Answer: True
This statement is true. Soil is crucial for all ecosystems as it supports plant life, which in turn sustains animal life, and it is a key factor in managing land health. Proper land management practices often focus on maintaining soil quality and preventing erosion.
In simple words: Soil is very important for nature and for taking care of land, so this statement is true.

🎯 Exam Tip: Highlight the dual role of soil in both ecological support (ecosystems) and human activity (land management) for a complete answer.

 

IV. Match the following:

 

Question 1.
a. Cotton - 1. Laterite Soils
b. Tea - 2. Desert Soils
c. Sugarcane - 3. Black Soils
d. Cactus - 4. Alluvial Soils
Answer: (a) 3, (b) 1, (c) 4, (d) 2
The correct matches are:
(a) Cotton with Black Soils (Black soils are rich in clay and moisture, ideal for cotton)
(b) Tea with Laterite Soils (Laterite soils are acidic and well-drained, suitable for tea)
(c) Sugarcane with Alluvial Soils (Alluvial soils are fertile and deep, good for sugarcane)
(d) Cactus with Desert Soils (Desert soils are sandy and dry, perfect for cacti)
In simple words: Cotton grows in black soil, tea in laterite soil, sugarcane in alluvial soil, and cactus in desert soil. Each plant likes a certain type of soil.

🎯 Exam Tip: For matching questions, link each item with its most appropriate partner based on characteristics or common associations.

 

V. Choose the incorrect statement from the following:

 

Question 1.
a) Basalt into slate caused by thermal metamorphism.
b) Chemical Sedimentary rocks are also called evaporates.
c) Taj Mahal in India was built with white marbles of Sedimentary rocks.
d) Rocks have been used by mankind throughout history.
Answer: (c) Taj Mahal in India was built with white marbles of Sedimentary rocks.
The incorrect statement is (c) because the Taj Mahal was built using white marble, which is a Metamorphic rock, not a Sedimentary rock. Metamorphic rocks form from existing rocks undergoing intense heat and pressure. Marble is a metamorphic form of limestone (a sedimentary rock).
In simple words: The wrong statement says the Taj Mahal was built with sedimentary rock. It was actually built with marble, which is a metamorphic rock.

🎯 Exam Tip: Pay close attention to distinctions between rock types; marble, being a metamorphosed limestone, is metamorphic, not sedimentary.

 

VI. Consider the following statements and choose the right option from the given ones:

 

Question 1. Statement (1): Petrology is a branch of geology. Statement (2): It deals with the Study of water researches.
a) 1 and 2 are correct and 2 explains 1
b) 1 and 2 are correct but, 2 does not explain 1
c) 1 is correct but, 2 is incorrect
d) 2 is correct but, 1 is incorrect.
Answer: (c) 1 is correct but, 2 is incorrect
Statement (1) is correct because petrology is indeed a branch of geology that focuses on the study of rocks. Statement (2) is incorrect because petrology deals with rocks, not water research; the study of water is called hydrology or hydrogeology. Therefore, only the first statement is true.
In simple words: Petrology is about rocks (correct), but it does not study water (incorrect). So, statement 1 is right, and statement 2 is wrong.

🎯 Exam Tip: Carefully read each statement and evaluate it independently before combining conclusions, especially when one statement is a definition.

 

VII. Give reasons for the following:

 

Question 1. Why soil is known as 'Skin of the earth'?
Answer: Soil is called the 'Skin of the Earth' because it forms the outermost layer of our planet. It is made up of a mixture of minerals, organic matter, water, and air, and it covers the Earth's surface just like skin covers a body. This vital top layer supports most terrestrial life and is constantly interacting with the atmosphere, hydrosphere, and lithosphere.
In simple words: Soil is like the Earth's skin because it covers the Earth's surface and is where life grows. It is the very top layer.

🎯 Exam Tip: When explaining metaphors like "skin of the Earth," clearly state what aspect of soil (its position, role, or composition) makes the comparison apt.

 

VIII. Distinguish the following:

 

Question 1. Black Soil and Red Soil.
Answer:

Black soils are typically clayey, dark in color, and excellent at holding water, making them great for cotton. Red soils, on the other hand, get their color from iron oxides and are formed from different parent rocks, often better for crops like millets due to their less water-retentive nature.
In simple words: Black soil comes from igneous rocks, holds water well, and is good for cotton. Red soil comes from metamorphic or crystalline rocks, has iron, and is good for millets.

🎯 Exam Tip: When distinguishing, use a table format to clearly present contrasting features side-by-side, focusing on origin, color, water retention, and suitable crops.

 

IX. Give short answers:

 

Question 1. Explain about Petrology.
Answer: Petrology is a specialized branch of geology that focuses on the study of rocks. The term "petrology" is derived from two Greek words: "Petrus," which means rock, and "Logos," which means study. Petrologists examine rocks to understand their formation, composition, structure, and classification, providing insights into Earth's history and processes.
In simple words: Petrology is the study of rocks. The word comes from Greek, where "Petrus" means rock and "Logos" means study.

🎯 Exam Tip: Define the term and break down its etymology to provide a comprehensive and memorable explanation.

 

Question 2. Name the layer in the Earth.
Answer: The main layers found on Earth that interact with each other are:

• **Lithosphere:** This is the solid, outermost shell of the Earth, including the crust and the uppermost part of the mantle.
• **Hydrosphere:** This encompasses all the water on Earth, whether it's in oceans, rivers, lakes, glaciers, or groundwater.
• **Atmosphere:** This is the layer of gases that surrounds the Earth, providing us with air to breathe and protecting us from solar radiation.
• **Biosphere:** This includes all life on Earth and the parts of the other spheres where life exists, from deep oceans to high in the atmosphere.

These layers constantly interact to create Earth's dynamic environment.
In simple words: The Earth has layers called the Lithosphere (land), Hydrosphere (water), Atmosphere (air), and Biosphere (living things).

🎯 Exam Tip: List the major Earth spheres and briefly define each, highlighting that they are interconnected systems.

 

Question 3. Explain the type of Igneous Rocks.
Answer: Igneous rocks are formed from molten magma or lava and are categorized into two main types:

• **Extrusive Igneous Rocks:** These rocks form when molten magma erupts onto the Earth's surface (as lava) and cools very quickly. Because of the rapid cooling, they typically have fine grains or a glassy texture. Basalt is a common example of an extrusive igneous rock.
• **Intrusive Igneous Rocks:** These rocks form when magma cools and solidifies slowly deep inside the Earth's crust. The slow cooling allows for the formation of larger mineral grains. Granite and diorite are well-known examples of intrusive igneous rocks.

Both types play a crucial role in the rock cycle, forming new crustal material.
In simple words: Igneous rocks are either extrusive (cool fast on the surface, making fine grains) or intrusive (cool slowly inside the Earth, making large grains).

🎯 Exam Tip: Clearly distinguish extrusive and intrusive rocks based on their cooling location (surface vs. underground) and resulting crystal size (fine vs. coarse).

 

X. Give a detailed answer for the following:

 

Question 1. What are the uses of soil?
Answer: Soil is an indispensable natural resource, vital for supporting life and numerous human activities on Earth. Its uses are extensive and fundamental to our survival:

• **Supports Plant Growth:** Soil provides the necessary nutrients, water, and anchorage for plants to grow. This includes crops that feed humans and animals, as well as forests that provide oxygen and timber.
• **Habitat for Organisms:** It serves as a home for countless microorganisms, insects, and animals, forming complex food webs and contributing to biodiversity.
• **Water Filtration:** Soil acts as a natural filter, purifying water as it percolates through its layers, helping to replenish groundwater resources.
• **Material for Construction:** Certain types of soil are used as raw materials in construction, such as clay for bricks and pottery, and sand for concrete.
• **Raw Material for Crafts:** It provides materials for handicraft works, including ceramics and traditional art forms.
• **Land Management:** Soil plays an important role in land management practices like agriculture, forestry, and urban development, impacting sustainability and productivity.

Ultimately, healthy soil is crucial for ecosystem stability, food security, and environmental balance.
In simple words: Soil is very useful. It helps plants grow, which feeds us and animals. It also gives us materials for pots and buildings, cleans water, and provides a home for many living things.

🎯 Exam Tip: When listing uses, cover both ecological benefits (plant growth, habitats, water filtration) and human applications (agriculture, construction, crafts).