IMPORTANT TERMS

Soil Profile                   Vertical section of the layers of the soil.

Weathering                  Breaking up of rocks by the action of wind, water, climatic changes etc.

Deforestation               Cutting down of trees.

Afforestation                The process of establishing forests in areas that have never been forested.

Reforestation               The restoration of forests in areas where forests were removed.

Ores                            Minerals from which metals can be extracted profitably.

Fossils                         Dead remains of plants and animals or their imprints in rocks.

Minerals                       Chemical substances naturally occurring in nature.

SOIL FORMATION

Soil is formed by the process of weathering. It takes millions of years in the process of formation of soil. There are four major layers of soil:-

Topsoil                It is the top most layer of soil which consists of humus, fine particles of sand, clay, air and water. This layer supports plants growth. Plants get all the required nutrients from this layer.

Subsoil                It lies below the top layer of soil and consists of small amount of humus, water and small pieces of rocks. Roots of some of the plants reach in this layer of soil.

Weathered Rock  It contains small pieces of rock along with some quantity of soil.

Bedrock               It contains large pieces of rocks and very small amount of water.

SOIL EROSION AND ITS CAUSES

Removal of top layer of soil by the action of wind, water, overgrazing etc. is called Soil Erosion.

Natural Causes

  • Running water    This causes maximum amount of Soil Erosion. When rain falls it carries topsoil with it. Due to removal of topsoil, land becomes unsuitable for farming.
  • Wind                  In deserts and open lands, wind causes a lot of erosion. Strong winds blow away the humus-rich topsoil.

Human activities

  • Overgrazing by cattle removes the plant cover from the soil. As a result, soil erosion increases.
  • Indiscriminate felling of trees increases soil erosion. When the trees are cut, the soil becomes loose; it is then easily carried away by wind and water.

SOIL CONSERVATION AND WAYS TO CONSERVE SOIL

Protection of soil against erosion is called soil conservation.

Ways of Soil Conservation

  • Planting more trees lessen soil erosion. Roots of the plants hold the soil thus, making it difficult for water and wind to take away the soil.
  • Avoid leaving the soil bare as wind blows off the soil from bare lands. Between cropping seasons they can be covered with grass.
  • Terrace farming is done in hills. The amount of soil lost is reduced as the soil eroded from one step is deposited on the other step.
  • Embankments are built along river to prevent soil erosion. The river water is unable to flood the nearby field. Soil is thus conserved from erosion through water.
  • Wind Breaks – Trees or hedges grown along the edges of field act as shield against strong winds. They prevent the soil from being blown away.

ROCKS AND MINERALS

Our Earth is made up of rocks. Rocks are made up of substances called minerals. Each rock contains different minerals. Minerals are chemical substances. They are found naturally on the Earth. There are many types of minerals.

  • Metallic minerals                   Silver, Gold, Platinum, Copper, Aluminum etc.
  • Non Metallic Minerals            Gypsum, Mica, Feldspar etc.
  • Crystalline Minerals               Sodium chloride (common salt which we eat), Potassium Nitrate (also known as Saltpetre- used as a fertilizers)
  • Non-Crystalline Minerals        Calcite, Haemitite, Bauxite etc.

Magnetite is a mineral that can attract other minerals towards itself. In general, such substances are called magnets. Magnets can attract substances made up of iron, cobalt and nickel.

MOHS SCALE       In 1882, Frederich Mohs created a scale that showed the hardness of certain minerals. On this scale, minerals with higher number are harder than the minerals with lower numbers. On the Mohs scale of hardness, diamond is ranked 1 and talc is ranked 10. So, diamond is the hardest mineral and talc is the softest of all minerals.

DIFFERENT TYPES OF ROCKS

Depending on the way they are formed, rocks are grouped under three types: Igneous, Sedimentary, Metamorphic

Sedimentary Rock:- Rocks that are formed by the deposition and solidification of sediment, especially sediments transported by water, ice and wind. These rocks are always formed in layers. Fossils are also found in sedimentary rocks. Almost 75% of the Earth’s surface is covered with sedimentary rocks. Examples of sedimentary rock are:

  • Sandstone        It is a soft stone formed of sand particles deposited close together. The most common mineral found in sandstone is Quartz.  Many of India’s Old buildings like Red Fort, Hawa Mahal etc. are built of red sandstone.
  • Conglomerate   It has rounded stones like pebbles, gravels, and even boulders cemented together into a mass. It is used in construction and also polished to make ornaments.
  • Shale               It is made of solidified clay and comes apart in thin layers. It is used in making bricks and cement.
  • Limestone         It is a rock with fine grains that are quite soft. It contains the mineral calcium and tiny bits of animal shells. Chalk is very common type of limestone.

Igneous Rock:- Rocks formed by cooling and solidification of magma or lava are called igneous rocks. Examples of Igneous rocks are:

  • Granite             It is very hard and is formed by the slow cooling of lava. It is used extensively as building material (as polished granite in kitchen counters and floors.)
  • Obsidian           It is smooth and glassy and is formed by quick cooling of lava. It is used in making jewellery and ornaments.
  • Pumice             It is formed from lava that is frothy with lot of air within it. It is the only rock that can float. It is used in making body scrubbers, to polish teeth, to polish floor and even as decorative piece.
  • Basalt               It is a dark colored, fine grained igneous rock. It makes up most of the oceanic crust of the Earth. It is formed when lava flows from volcanoes or from cracks in the Earth’s surface and then hardens. It is used in construction of buildings.

Metamorphic Rocks:- These rocks are formed by ‘changing the forms’ i.e., due to physical and chemical changes in igneous and sedimentary rocks. These changes occur due to intense heat and pressure inside the Earth crust. Examples of Metamorphic rocks are:-

  • Marble              It is formed from sedimentary rock called limestone.  It is strong and it can be polished. It comes in various colours. It is used for making statues, flooring, ornaments etc.
  • Slate                It is formed from sedimentary rock called Shale. It is usually black or grey in colour. It is used for making bricks, cement and blackboard.
  • Gneiss             It is formed from sedimentary rock called Granite.
  • Quartzite                    It is formed from sedimentary rock called sandstone. It is such a hard rock that it can scratch steel. It is used to make statues, in watches, as gemstones, in making glass.

COAL and PETROLEUM

Coal and petroleum are also obtained from rocks.

Coal

Coal is a kind of sedimentary rock. Millions of years ago, dead remains of plants and animals got buried deep under the EARTH. Under intense heat and pressure they transformed into coal. It is used to cook, to generate electricity in thermal power plants and in steel plants to make steel.

Coal has four major varieties:

  • Anthracite          It is the best variety of coal. It produces lot of heat and minimum smoke on burning. It is also known as hard coal.
  • Bituminous         It is soft coal. It burns with a lot of smoke.
  • Lignite               It forms the largest portion of the World’s total coal reserves. It is a soft brownish-black coal.
  • Peat                  It was the earliest type of coal to be formed. It is not used very often as it gives very less heat and burns with a lot of smoke.

Petroleum

It is also called as ‘rock oil’ or ‘black gold’. It was obtained from dead remains of plants and animals buried deep under the SEA millions of years ago. Petroleum cannot be used in natural state and hence is refined into CNG, LPG, Petrol, Diesel, Wax etc. Natural gas is always found above the petroleum reserves in the oil wells.

USES OF ROCKS AND MINERALS

  • Rocks are used as building material   e.g. Granite, Sandstone
  • Rocks give us fuel.                           e.g. Coal
  • Rock give us useful metals                e.g. Iron, copper, gold, silver etc.
  • Minerals serve as fertilizers               e.g. Saltpetre (potassium nitrate),
  • Minerals are used as gemstones       e.g. Diamond, ruby, emerald, sapphire, topaz etc

INTRESTING FACTS

  • There are more microorganisms in a handful of soil than there are people on earth.
  • It takes 500 years to produce just under an inch of topsoil; this is the most productive layer of soil.
  • Soil acts as a filter for underground water, filtering out pollutants.
  • Earth’s moon is made out of igneous rocks.