Inside Our Earth

 

INTERNAL STRUCTURE OF THE EARTH

The Earth is like a giant onion with several layers inside it. These layers make up its internal structure. By studying these layers, scientists can gain knowledge that may help in predicting natural disasters, finding valuable resources, and advancing our understanding of the planet. It will also help in learning about its past, present, and future.

Scientists use several methods to study the Earth's internal structure. One method is by examining seismic waves that travel through the Earth during earthquakes. By measuring how these waves move and change as they pass through different layers, they can learn about the Earth's composition and structure. They also use information from drilling deep into the Earth's crust and studying rocks and minerals found there.

 

CRUST

The crust is the thinnest of all the layers of the Earth, with an average thickness of with an average thickness of 35 km of continental crust and 5 km of oceanic crust. Made up of rocks and soil, it is this layer that supports life. The crust can be further divided into two parts-the upper part of the crust comprises continental masses and the lower part comprises ocean floors. The continents are made of silica and alumina, and are therefore called sial (si-silica and al-aluminium). The ocean floors are made up of silica and magnesium, and are therefore also called sima (si-silica and ma-magnesium). Sial extends as far as 35 km. It is much thicker than sima, which is barely 5 km thick. Scientists believe that when the Earth was formed, heavier rocks sank to form the ocean floor, while the lighter rocks settled on top to form the continental masses.

 

MANTLE

Mantle lies below the crust. This layer extends up to a depth of 2900 km and is extremely hot. This is because the temperature inside the Earth rises with depth. As we go deeper into the Earth, the temperature increases by 1°C every 32 m. The layers also become denser as we go down. The mantle is made up mainly of silicon and magnesium. Rocks are found in molten form inside the mantle. Such molten rocks are called magma. The lighter crust is said to be floating on the molten, heavier mantle. The mantle is further divided into two parts - upper mantle and lower mantle. The upper mantle is known as aesthenosphere

 

CORE

The core is the innermost layer of the Earth. It is made up of nickel and iron and is therefore also called nife (ni-nickel and fe-ferrous or iron). Many experts attribute the magnetic properties of the Earth to the presence of nickel and iron. The core is extremely hot; temperatures inside the core can reach 2000-5000° C. It has a radius of 3500 km. The core is further divided into outer core and inner core. The outer layer of the core is in molten state due to extremely high temperatures. It is 2300 km thick. The inner core (1200 km thick) is solid due to the pressure exerted by the other outer layers of the Earth. The extremely high temperatures in this zone cause materials in the outer core and inner mantle to move around.

Geology is the study of the formation of the earth, it's structure and composition and the types of processes acting on it. Based on the Earth's volume, the core forms only 15 percent, the mantle occupies 84 percent and the crust makes up the remaining 1 percent.

 

ROCKS AND MINERALS

Minerals are naturally occurring substances found in the Earth's crust. They have a definite chemical composition and physical properties. Minerals can be organic or inorganic. Organic minerals are formed from the decomposition of dead animals and plants trapped inside the Earth. Coal, petroleum, and natural gas are formed this way. As these minerals are sources of energy, they are also known as fossil fuels. Inorganic minerals can be divided into metallic (iron, gold, aluminium) or non-metallic (silicon, sulphur).

 

 

 

  

Organic minerals  and Inorganic minerals
Feature	Organic minerals	Inorganic minerals
Formation	Formed from the decomposition of dead animals and plants trapped inside the Earth	Formed through geological processes without the involvement of living organisms
Examples	Coal, petroleum, natural gas.	Metallic: Iron, gold, aluminum Non-metallic: Silicon, sulfur
Sources	Sources of energy; also known as fossil fuels	Can be found in various geological formations

 

 

Rocks are made up of one or more minerals. So we can say, rocks are naturally existing masses of minerals. They can be hard such as granite and marble, or soft and loose such as chalk, clay, and salt. As rocks are made of one or more minerals, they do not have a definite chemical composition. Earth's crust is made up of rocks of different sizes, colours, and textures. Minerals extracted from these rocks can be used for many purposes. For example, coal is a mineral that can be used as a fuel. Gold and iron are minerals that are widely used in industries. Minerals can also be used to make medicines and chemicals. The most common rock-forming minerals are called silicates. On the basis of their mode of formation, rocks can be classified into three types - igneous, sedimentary, and metamorphic.

 

Petrology	It is the branch of geology which involves the study of rocks and the conditions under which they form.
Weathering	It is the process of breaking down of rocks into smaller pieces due to the action of temperature, rainfall, wind, water, etc., as well as plants and animals.
Ore	An ore is a rock which has a high concentration of a mineral or metal in it, which can be extracted easily and refined for use.

 

IGNEOUS ROCKS

The word igneous comes from the Latin word ignis meaning 'fire'. These are rocks formed by the cooling of molten magma. Igneous rocks are also called primary rocks as they were the first rocks to be formed and all other rocks are formed from them. They usually occur as large shapeless masses. They are hard and non-porous, which makes them ideal for making buildings, roads, etc. They are usually crystalline or glassy in appearance. Metallic ores such as iron, gold, and silver ores are often found in igneous rocks. Such rocks do not have plant or animal remains. Igneous rocks can be divided into two types, depending on the manner in which they are formed:

 

(i) Extrusive igneous or volcanic rocks: These are rocks formed by the rapid cooling of molten lava as it comes out of a volcano and falls on the Earth's surface. Basalt rocks found in the Deccan Plateau were formed in this manner. As they are formed due to rapid cooling of lava, extrusive igneous rocks have very fine grains.

 

(ii) Intrusive igneous or plutonic rocks: These are rocks formed by the slow cooling of molten magma deep inside the crust. As the molten magma cools slowly, intrusive igneous rocks have large grains. Granite is an example of this type of rocks. It is used to make grinding stones with which we can powder spices or grains and turm them into paste.

 

 

SEDIMENTARY ROCKS

The word sedimentary comes from the Latin word sedimentum meaning 'settle down'. Sedimentary rocks are formed from fragments of other rocks. Rocks often break down into smaller particles due to the action of water, wind, plants, animals, etc. Such particles are called sediments. The loose sediments are transported by wind, water, etc., and deposited in different places. Over time, these sediments get compressed and form layers of rocks. Such layered rocks are called sedimentary or stratified rocks. As sedimentary rocks are formed from other rocks, they are also called secondary rocks. They are the most widely available rocks.

 

Sedimentary rocks are layered, soft, and porous. As they are mostly formed under water, they have wave-like patterns and mud cracks on the surface. Often plant and animal fossils are found compressed in these rocks. Therefore, they are a good source of fossil fuels such as coal, petroleum, and natural gas. Sandstone is an example of a sedimentary rock. It is formed when grains of sand get compressed over a period of time. Limestone, clay, and shale are also formed by sediments of other rocks.

 

Remains of dead plants and animals often get trapped between layers of sedimentary rocks. Such remains are called fossils.

 

ΜΕΤΑMORPHIC ROCKS

Metamorphic rocks are formed when igneous or sedimentary rocks are subjected to high heat, pressure, or both. The word metamorphic comes from the Greek word metamorphose meaning 'change of form'. Clay turns into slate under conditions of great heat and pressure, sandstone turns into quartzite, and limestone turns into marble. Granite turns into gneiss, while basalt forms schist.

 

Metamorphic rocks are formed deep inside the Earth and take a long time to form. They have different physical and chemical properties compared to the parent rocks. They are often harder and bulkier compared to the igneous or sedimentary rocks that formed them. The Deccan Plateau is made up of igneous and metamorphic rocks, while the Himalayas are made up of sedimentary rocks.

Metamorphic rocks

 

ROCK CYCLE

We know igneous rocks can give rise to sedimentary rocks and both can change into metamorphic rocks. This natural process of transformation of one rock type into another is called the rock cycle. Igneous rocks are formed when molten magma cools down and solidifies. They are the parent rocks from which all other rocks are formed. Igneous rocks break down into small particles or sediments by the action of wind, water, plants, etc. The smaller particles are transported and deposited in different places. Over time, the particles get compressed to form layered or sedimentary rocks.

Metamorphic rocks are formed from igneous or sedimentary rocks when they are subjected to high heat or pressure. As metamorphic rocks are formed deep inside the Earth, the high temperature and pressure can transform them once again into molten magma. This magma can again cool down to form igneous rocks and start the cycle all over again.

 

USES OF ROCKS AND MINERALS

1. Minerals provide plants with the nutrients they need to grow.

2. Minerals such as coal and petroleum are important sources of fuel.

3. Many minerals are used in jewellery.

4. Rocks are extensively used in construction of roads, houses, etc.

5. Ores are widely used in industries to obtain metals and minerals.

6. Some sedimentary rocks are good sources of fertilisers.

 

 

New Terms
Crust	The thinnest, outermost layer of the Earth on which we live; it is made up of rocks and soil.
Sial	Continental masses; made up of silica and alumina.
Sima	Ocean floors; made up of silica and magnesium.
Mantle	Layer beneath the crust where molten rocks are found; extends up to a depth of 2900 km.
Core	Innermost layer of the Earth.
Nife	Another name for core as it is made up of nickel and iron.
Minerals	Naturally occurring substances found in the Earth's crust.
Rocks	Naturally existing masses of minerals.
Igneous rocks	Formed by the cooling of molten magma.
Extrusive igneous rocks	Formed by the rapid cooling of molten lava.
Intrusive igneous rocks	Formed by the slow cooling of molten magma deep inside the crust.
Sedimentary rocks	Formed when fragments of other rocks get compressed.
Metamorphic rocks	Formed when igneous or sedimentary rocks are subjected to high heat, pressure, or both.
Rock cycle	The natural process of transformation of one rock type into another.

 

 

1. What method is commonly used by scientists to study the Earth's internal structure?

A. Satellite photography

B. Fossil analysis

C. Examining seismic waves

D. Watching volcanic eruptions

Answer: C. Examining seismic waves

Explanation: Seismic waves generated during earthquakes help scientists understand the Earth's layers by observing how the waves change as they pass through different materials.

 

2. Which is the thinnest layer of the Earth?

A. Mantle

B. Inner core

C. Outer core

D. Crust

Answer: D. Crust

Explanation: The crust is the outermost and thinnest layer, averaging about 35 km for continental crust and 5 km for oceanic crust.

 

3. What is the continental crust primarily made of?

A. Nickel and iron

B. Silica and alumina

C. Sulphur and carbon

D. Silicon and magnesium

Answer: B. Silica and alumina

Explanation: The continental crust (sial) is rich in silica and alumina.

 

4. What term is used for the oceanic crust due to its composition?

A. Sial

B. Lithosphere

C. Sima

D. Mantle

Answer: C. Sima

Explanation: The oceanic crust is rich in silica and magnesium, hence it is called sima.

 

5. What is the approximate depth of the Earth's mantle?

A. 35 km

B. 1000 km

C. 2900 km

D. 5000 km

Answer: C. 2900 km

Explanation: The mantle lies below the crust and extends to about 2900 km in depth.

 

6. What is the upper part of the mantle called?

A. Asthenosphere

B. Lithosphere

C. Troposphere

D. Mesosphere

Answer: A. Asthenosphere

Explanation: The upper mantle is known as the asthenosphere and consists of semi-molten rock.

 

7. What is the main composition of the Earth's core?

A. Silica and magnesium

B. Silicon and aluminium

C. Nickel and iron

D. Carbon and hydrogen

Answer: C. Nickel and iron

Explanation: The core is composed mainly of nickel (ni) and iron (fe), hence called nife.

 

8. Why is the Earth's core extremely hot but solid at the center?

A. It is made of lava

B. Due to lack of space

C. Due to high pressure from outer layers

D. Because of external radiation

Answer: C. Due to high pressure from outer layers

Explanation: The intense pressure from the overlying layers makes the inner core solid despite high temperatures.

 

9. Which layer of the Earth is responsible for its magnetic properties?

A. Crust

B. Mantle

C. Core

D. Atmosphere

Answer: C. Core

Explanation: The presence of iron and nickel in the Earth's core is believed to generate Earth's magnetic field.

 

10. Which layer occupies the largest volume of the Earth?

A. Crust

B. Inner core

C. Mantle

D. Outer core

Answer: C. Mantle

Explanation: The mantle occupies about 84% of Earth’s volume, making it the largest layer.

 

11. What is the name given to molten rock inside the mantle?

A. Lava

B. Magma

C. Granite

D. Basalt

Answer: B. Magma

Explanation: Inside the mantle, molten rock is known as magma. When it erupts onto the surface, it is called lava.

 

12. Which of the following best defines a mineral?

A. A man-made substance with changing properties

B. A naturally occurring substance with definite chemical composition

C. A liquid found in oceans

D. A gas used in industries

Answer: B. A naturally occurring substance with definite chemical composition

Explanation: Minerals are natural substances found in the Earth's crust with fixed chemical and physical properties.

 

13. Coal, petroleum, and natural gas are examples of:

A. Inorganic minerals

B. Volcanic materials

C. Metallic ores

D. Organic minerals or fossil fuels

Answer: D. Organic minerals or fossil fuels

Explanation: These are organic minerals formed from the decomposition of plants and animals over millions of years.

 

14. Which of the following is an example of a metallic mineral?

A. Sulphur

B. Coal

C. Gold

D. Natural gas

Answer: C. Gold

Explanation: Gold is a metallic mineral; others like iron and aluminium also fall into this category.

 

15. What percentage of Earth’s volume is made up by the crust?

A. 15%

B. 1%

C. 84%

D. 50%

Answer: B. 1%

Explanation: The Earth's crust is only about 1% of the planet’s total volume.

 

 

16. Which of the following is an example of an organic mineral?

A. Iron

B. Coal

C. Silicon

D. Gold

Answer: B. Coal

Explanation: Organic minerals like coal are formed from the decomposition of dead plants and animals trapped inside the Earth and are used as fossil fuels.

 

17. What are inorganic minerals formed through?

A. Animal remains

B. Chemical synthesis

C. Geological processes

D. Solar energy

Answer: C. Geological processes

Explanation: Inorganic minerals are formed through natural geological processes without the involvement of living organisms.

 

18. Which of the following is a non-metallic inorganic mineral?

A. Gold

B. Iron

C. Aluminium

D. Silicon

Answer: D. Silicon

Explanation: Non-metallic minerals include substances like silicon and sulfur that are not metals but occur naturally in the Earth's crust.

 

19. What is the primary difference between rocks and minerals?

A. Rocks are synthetic; minerals are natural

B. Rocks have definite chemical composition

C. Rocks are made up of one or more minerals

D. Minerals are softer than rocks

Answer: C. Rocks are made up of one or more minerals

Explanation: Rocks are naturally occurring solid masses composed of one or more minerals and do not have a definite chemical composition.

 

20. What is the most common group of rock-forming minerals?

A. Sulfides

B. Carbonates

C. Silicates

D. Nitrates

Answer: C. Silicates

Explanation: Silicates are the most abundant group of rock-forming minerals found in the Earth's crust.

 

21. Which of the following rocks is classified as soft and loose?

A. Granite

B. Marble

C. Chalk

D. Basalt

Answer: C. Chalk

Explanation: Chalk is a soft and loose rock compared to hard rocks like granite and marble.

 

22. What is petrology the study of?

A. Minerals

B. Earthquakes

C. Fossils

D. Rocks

Answer: D. Rocks

Explanation: Petrology is the branch of geology concerned with the study of rocks and the conditions under which they form.

 

23.What is weathering in geological terms?

A. Melting of rocks

B. Breaking down of rocks into smaller pieces

C. Formation of fossils

D. Transportation of minerals

Answer: B. Breaking down of rocks into smaller pieces

Explanation: Weathering is the process by which rocks are broken down due to natural forces like wind, water, temperature, and living organisms.

 

24. What is an ore?

A. A type of rock used for decoration

B. A rock that contains minerals

C. A mineral with no commercial use

D. A rock rich in minerals or metals that can be profitably extracted

Answer: D. A rock rich in minerals or metals that can be profitably extracted

Explanation: An ore is a rock containing a high concentration of a valuable mineral or metal that can be economically extracted and refined.

 

25.Which type of rock is formed due to change in form by heat and pressure?

A. Igneous

B. Sedimentary

C. Metamorphic

D. Volcanic

Answer: C. Metamorphic

Explanation: Metamorphic rocks are formed when existing rocks are changed in form through heat and pressure over time.

 

26. Which type of rock is called the ‘primary rock’ as all other rocks are formed from it?

A. Sedimentary rock

B. Igneous rock

C. Metamorphic rock

D. Fossil rock

Answer: B. Igneous rock

Explanation: Igneous rocks are called primary rocks because they are the first rocks to form and all other rocks originate from them.

 

27.Which of the following rocks is formed by the rapid cooling of lava on the Earth's surface?

A. Granite

B. Marble

C. Basalt

D. Slate

Answer: C. Basalt

Explanation: Basalt is an extrusive igneous rock formed by the rapid cooling of lava that flows out of a volcano.

 

28. Which of the following rocks is likely to contain fossils?

A. Basalt

B. Granite

C. Sandstone

D. Quartzite

Answer: C. Sandstone

Explanation: Fossils are commonly found in sedimentary rocks like sandstone, as they form from compressed layers of sediments where remains of plants and animals may get trapped.

 

29.Which metamorphic rock is formed from limestone?

A. Marble

B. Slate

C. Quartzite

D. Schist

Answer: A. Marble

Explanation: When limestone undergoes heat and pressure, it changes into marble, a metamorphic rock.

 

30. Which rock is used to make grinding stones due to its hardness?

A. Slate

B. Basalt

C. Granite

D. Clay

Answer: C. Granite

Explanation: Granite is an intrusive igneous rock known for its hardness and is often used to make grinding stones and construction materials.

 

31. What does the term “sedimentary” literally mean?

A. Solidify

B. Evaporate

C. Settle down

D. Crystallize

Answer: C. Settle down

Explanation: “Sedimentary” comes from the Latin word sedimentum, which means “settle down,” indicating how these rocks form from settled sediments.

 

32.Which of the following is an example of a plutonic (intrusive) igneous rock?

A. Basalt

B. Granite

C. Sandstone

D. Schist

Answer: B. Granite

Explanation: Granite is a plutonic or intrusive igneous rock formed by the slow cooling of magma deep inside the Earth.

 

33. Which process leads to the formation of sedimentary rocks?

A. Melting

B. Crystallization

C. Compression of sediments

D. Magma solidification

Answer: C. Compression of sediments

Explanation: Sedimentary rocks form when sediments are deposited and compressed over time into layers.

 

34. Slate is formed from which parent rock?

A. Sandstone

B. Limestone

C. Clay

D. Basalt

Answer: C. Clay

Explanation: Clay transforms into slate under high heat and pressure, making slate a metamorphic rock.

 

35. Which of these statements correctly describes the rock cycle?

A. Rocks transform from one form to another in a fixed sequence.

B. Rocks are only formed once and do not change.

C. Sedimentary rocks are parent rocks of all types.

D. The transformation of rocks is a continuous and natural process.

Answer: D. The transformation of rocks is a continuous and natural process.

Explanation: The rock cycle describes how rocks change from one type to another through processes like weathering, compression, heat, and melting in a continuous loop.