4th Class Science Rocks and Soil / चट्टानें और मिट्टी Rocks and Soil

LEARNING OBJECTIVES

This lesson will help you to:—

• understand what are rocks.
• know about the various uses of rocks.
• understand different types of rocks.
• know different types of soil.
• learn about different layers of soil.

Historical Preview

• The earth is approximately 4.8 billion years old. This has been found out from the sample of the rocks collected.
• The first geologist on the moon was Harrison Schmitt who was part of the Apollo 17 mission. From the rock samples he collected, scientist have been able to learn many things about the moon.

QUICK CONCEPT REVIEW

Why are we studying about rocks?

If we took all the rocks away, we would have a miserable life. We use rocks for roads, metals, jewelry, tombstones, building materials, cosmetics, and many, many more things. Most of the famous sculptures of the world are made from blocks of stones such as granite and marble. Did you know that the Great Wall of China and the Taj Mahal are made out of rocks? If we did not have rocks, this earth mould be pretty empty. We can also collect rocks as a hobby. 

Amazing Facts

• The diamond is the hardest natural substance found on earth.
• Quartz is one of the most common minerals on earth.
• It takes more than 500 years to form 2 centimeters of topsoil.

Soil has its own colour palette. Soil comes in: red, yellow, black, brown, grey, and white.   

FUN TRICKS

Shortcut to problem solving                           

Think of a chocolate chip cookie as a rock. The cookie is made of flour, butter, sugar & chocolate. The cookie is like a rock and the flour, butter, sugar & chocolate are like minerals. All rocks are made of minerals

How are rocks formed?                             

Different types of rocks are formed in different ways.

• After the eruption of volcanoes a liquid comes out which is called magma. When magma cools and solidifies it forms igneous rock.

Granite, basalt are examples of igneous rocks.    

• Sediment deposited over time, often as layers at the bottom of lakes and oceans, forms sedimentary rocks.

Examples of sedimentary rocks include sandstone, shale, and chalk.

• Metanrorphic rocks are rocks that shape up due to intense heat and pressure. When the earth's crust moves, it causes rocks to get squeezed so hard that the heat causes the rock to change.

Examples of metamorphic rocks include marble, quartzite and slate.

USES OF ROCKS

Rocks have been used by human beings for millions of years. Rocks are used for making tools and weapons and various construction materials. Man gets metals from rocks and makes them into jewelry. Rocks are also used for building roads and bridges.

Misconcept/Concept

Misconcept: All rocks are the same, and it’s hard to tell how they originated.

Concept: Rocks can be distinguished in different types, based on their origins and composition.

Misconcept: Rocks are dull and unattractive

Concept: Beautiful gemstones and precious metals are also derived from rocks.

Misconcept: Soil and dirt are the same.

Concept: While soil can germinate plants. Dirt is dead and cannot germinate plants.

The Importance of Rocks and Minerals

WHAT IS SOIL?

Soil is the top layer of the earth's surface, like icing o a cake. In our garden's backyard, we play on grass and soil. Soil is made from rocks that are broken into tiny pieces. It is a mixture of rock particles, as well as organic matter like dead leaves, animal manure, roots, twigs, dead bugs and many insects and worms. Soil is often called the "living skin" of the earth. It is capable of supporting plant life and is vital to life on earth.

TYPES OF SOIL

LAYERS OF SOIL

Soil is made up of distinct layers. Each layer of the soil is called horizon.

The soil can be divided into four main layers: topsoil, subsoil, parent material and bedrock. Topsoil contains the most humus, which is the dark part of the soil that is rich in nutrients. This layer is made up of minerals and decomposed organic matter and it is also very dark in colour. This is the layer where roots of many plants grow.

Under the topsail are several layers that make up the subsoil. These layers tend to be sandier, and have less humus. Under the subsoil is parent material. Under parent material lays bedrock, which is solid rock. Plant roots are not found in this layer.

SOIL EROSION

Soil erosion refers to the erosion and degradation of land as a result of human activities. It is a major issue that affects the natural environment and agriculture. Soil erosion leads to washing away of top soil, poor drainage and huge organic loss in the soil.

DEFORESTATION

Deforestation is when humans remove or clear large areas of forest lands for agriculture or residential purposes. Cutting down of forest leads to soil erosion and increase in temperature. About half of world's original forests had been destroyed and millions of animals and living things have become endangered due to deforestation.