Soil and Rocks as Natural Resources - Class 5 Notes & Olympiad Questions

Soil

a) Soil, the uppermost layer of the Earth's surface, is a loose material composed of various substances.
b) It consists of a wide range of minerals, remnants of plants and animals, as well as water and air. This natural resource plays a crucial role in supporting life on our planet.
c) Soil is a mixture of both living (biotic) and non-living (abiotic) components. The biotic components include organisms like bacteria, fungi, insects, and earthworms, which contribute to the decomposition of organic matter in the soil.
d) Various minerals, such as quartz and clay, make up the non-living part of the soil.
e) Soil is porous, meaning it contains tiny pores or spaces. These pores allow water and air to move through the soil, which is vital for the growth of plants and the survival of many organisms.

Uses of Soil

a) Plants rely on soil to obtain nutrients and water for their growth. The roots of plants extend into the soil, absorbing water and essential minerals that are dissolved in it.
b) Soil acts as a habitat for numerous organisms. It provides shelter and a source of food for insects, worms, and microorganisms, forming a complex ecosystem underground.
c) Soil plays a crucial role in agriculture and food production. Farmers rely on fertile soil to grow crops, as it provides the necessary nutrients and support for plant growth.

Formation of Soil

Soil formation is a gradual and continuous process that occurs over many centuries.

a) It involves the breakdown of rocks into smaller particles through weathering or rock disintegration.
b) Weathering occurs through various natural factors such as temperature changes, water, wind, and other environmental forces. For example, during the day, rocks heat up, and at night, when the temperature cools down, they contract and create cracks.
c) Rainwater enters these cracks and freezes, widening the cracks and breaking rocks into smaller pieces.
d) Moving water can carry away these rock fragments, leading to further breakdown.
e) The rock particles mix with organic matter from decaying plants and animals, providing nutrients for the soil.
f) Over time, the mixture undergoes transformation and microbial activity, resulting in the formation of fertile soil.

Layers of Soil

Soil has different layers called horizons.

1. Horizon O - Humus

a) This is a thin, dark layer that is very fertile.
b) It is made up of decomposed matter, like dead plants and animals.
c) The humus layer provides nutrients to plants and helps them grow.

2. Horizon A - Topsoil

a) The topsoil is the layer where plants grow their roots.
b) It is rich in organic material, including the humus layer.
c) Topsoil is soft and porous, which means it can hold enough air and water for plants to use.

3. Horizon B - Subsoil

a) The subsoil is found beneath the topsoil. It contains larger-sized particles like gravel, rocks, and stones.
b) Subsoil allows water to seep through it, moving it deeper into the ground.

4. Horizon C - Regolith

a) Regolith is made up of small pieces of rocks. It is not very good at letting water pass through it.

5. Horizon D - Bedrock

a) Bedrock is the layer of solid rock that lies beneath all the other layers. It is the hard foundation of the soil and is made up of big rocks.

Soil Erosion

a) Soil erosion is the process where the fertile top layer of soil is removed by the action of natural elements like wind and water, or by human activities.
b) Soil erosion can make the land less suitable for growing plants and disrupt ecosystems.

Soil Conservation

Soil conservation is about taking care of our soil to keep it healthy and protect it from getting washed or blown away. Some key points about soil conservation are:

a) To protect the soil, we should avoid cutting down trees, especially for building things like houses. Trees are important because their roots help hold the soil together.
b) When too many animals, like cows or sheep, eat all the grass in an area, it can leave the soil bare and vulnerable to erosion. So, it's important to make sure there are not too many animals grazing in one place.
c) Farmers can plant special crops called cover crops. These crops are planted in fields when the main crops are not growing. They cover the soil, protecting it from erosion caused by wind or heavy rain. Cover crops also add nutrients to the soil, making it healthier for future crops.
d) Along rivers, building embankments can help control the flow of water. This prevents the river from flooding and washing away the soil along its banks.

Rocks

a) Rocks are an important part of the Earth's crust, which is the outermost layer of the Earth. It is the solid surface on which all known life exists.
b) Rocks play an important role in shaping the Earth's landscape and provide valuable resources for human use.
c) The Earth's crust is made up of different types of rocks. These rocks can be grouped into three main categories: igneous, sedimentary, and metamorphic rocks.
d) Each type of rock has its own characteristics, such as hardness, texture, and colour. They can also contain valuable minerals and fossils.

Types of Rocks

1. Igneous Rocks

a) Igneous rocks are formed from hot magma or lava that cools and solidifies.
b) The Earth's interior is very hot and contains a mixture of molten and semi-molten rock called magma.
c) Sometimes, the magma rises to the surface through cracks in the Earth's crust or through volcanic eruptions, and when it flows out, it is called lava.
d) As the magma or lava cools, it solidifies and transforms into igneous rocks.
e) There are different types of igneous rocks, such as granite, pumice, and basalt, each with its own characteristics.
f) They are significant components of the Earth's crust and have various uses in construction, decoration, and manufacturing.

2. Sedimentary Rocks

a) Sedimentary rocks are formed through the process of weathering, where rocks break down over time due to the forces of wind, rain, and heat.
b) The broken-down particles, called sediments, are carried by wind and water to bodies of water like rivers, lakes, and oceans, where they settle and accumulate in layers.
c) Over millions of years, these layers of sediments become compressed and solidified, forming sedimentary rocks.
d) Different types of sedimentary rocks, such as conglomerate, sandstone, shale, and limestone, are formed depending on the composition of the sediments and the environment in which they settle.

3. Metamorphic Rocks

a) Metamorphic rocks are formed when rocks deep inside the Earth, like igneous and sedimentary rocks, experience extreme heat and pressure.
b) These conditions cause the rocks to change and transform. The word "metamorphic" means that these rocks undergo a process of change.
c) Some examples of metamorphic rocks are quartzite, marble rock, slate, and gneiss.

Minerals

a) Minerals are natural substances that make up rocks. They can be found on or deep inside the Earth.
b) Some minerals, like potassium and magnesium, are extracted from sea salts found in seawater. Other minerals, such as diamond and graphite, are found below the Earth's surface.
c) Rocks can be composed of one or many minerals. Some rocks contain valuable metals like iron, copper, and aluminium. These metals are part of the rock structure.
d) Rocks that contain large quantities of useful metals, along with other unwanted substances, are called ores.

Types of Minerals

There are two types of minerals: metallic minerals and non-metallic minerals.

Metallic minerals contain metals such as iron, copper, gold, and aluminium. These are used to make things like wires, coins, pots and pans, and parts of vehicles.

Non-metallic minerals do not contain metals and have different uses. For example, diamond is used in jewellery; graphite, in the production of pencils and quartz is commonly used in the production of glass, ceramics, and electronics.

Some examples of rocks and metals obtained from them: