Water Cycle

The sun's heat causes evaporation of water into vapour.When the water vapour cools down,it condenses and forms clouds.Form there it may fall on the land or sea in the form of rain,snow or sleet.

    The process by which water continually changes its form and circulates between oceans, atmosphere and land is known as the water cycle.

Terrarium: It is an artificial enclosure for keeping small house plants.

                A Terrarium

Wind

The movement of air from high pressure area to low pressure areas is called wind.You can see wind at work as it blows dry leaves down the pavement or uproots trees during a storm.Sometimes when the wind blows gently you can even see it blowing away smoke or fine dust.At times wind can be so strong that it is difficult easy to hold an umbrella on a windly day.Think of some other examples when strong winds have created problems for you.Winds can be broadly divided into three types.

1.  Permanent wind: The trade winds, westerlies and easterlies are the permanent winds.

These blow constantly throughout the year in a particular direction.

Major pressure belt and Wind System

2.  Seasonal winds:These winds change their direction in different seasons.For example mansoons in India.

3.  Local winds:These blow only during a particular period of the day or year in a small area.For example, land and sea breeze.Do you recall the hot and dry local wind of northern planes of India?It is called loo.

Air Pressure

You will be surprised to know that air above us presses us with a great force on our bodies. However, we don't even feel it.

This is because the air presses us from all directions and our body exerts a counter pressure.

    Air pressure is defined as the pressure exerted by the weight of air on the earth's surface .As we go up the layers of atmosphere, the pressure falls rapidly. The air pressure is highest at sea leval and decreases with height. 

Horizontally the distribution of air pressure is influenced by temperature of air at a given place.In areas where temperature is high the air gets heated and rises. This creates a low - pressure area. Low pressure is associated with cloudy skies and wet weather.

In areas having lower temperature, the air is cold.It is therefore heavy air sinks and creates a high pressure area.

High pressure is associated with clear and sunny skies.

The air always moves from high pressure areas to low pressure areas.

On the moon there is no air and hence no air pressure.

Astronauts have to wear special protective space suits filled with air when they go to the moon.If they did not wear these space suits,the counter pressure exerted by the body of the astronauts would make the blood vessels burst.The astronauts would bleed.

Temperature

The temperature you feel everyday is the temperature of the atmosphere. The degree of hotness and coldness of the air is known as temperature.

     The temperature of the atmosphere changes not only between day and night but also from season to season. Summers are hotter than winters.

     An important factor that influences the distribution of temperature is isolation.

Isolation is the incoming solar energy intercepted by the earth.

     The amount of isolation decreases from the equator towards the poles.

Therefore, the temperature decreases in the same manner.Now do you understand why poles are covered with snow?If the earth's temperature rises too high ,it would become too warm for some crops to grow.Temperature in cities is much higher than that of villages, The concrete and metals in buildings and the asphalt of roads get heated upr during the night.

      Also,the crowded high buildings of the cities trap the warm air and thus raise the temperature of the cities.

The standard unit of measuring temperature is degree Celsius. It was invented by Anders Celsius. On the Celsius scale the water freezes at 0°C and boils at 100℃.

Atmosphere

Our atmosphere is divided into five layers starting from the earth's surface. These are Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.

Troposphere: This layer is the most important layer of the atmosphere. Its average height is 13 Km. The air we breathe exists here.

Almost all the weather phenomena like rainfall,fog and hailstorm occur in this layer.

Stratosphere: Above the troposphere lies the stratosphere. It extends up to a height of 50 Km.This layer is almost free from clouds and associated weather phenomenon.making conditions most ideal for flying aeroplanes.One important feature of stratosphere is that it contains a layer of ozone gas.We have just learnt how it protects us from the harmful effect of the sun rays.

Mesosphere:This is the third layer of the atmosphere. It lies above the stratosphere. It extends up to the height of 80 Km. meteorites burn up in this layer on entering from the space.

Thermosphere: In thermosphere

temperature rises very rapidly with increasing height. Ionosphere is a part of this layer.It extends between 80-400Km. This layer helps in radio transformation. In fact,radio waves transmitted from the earth are reflected back to the earth by this layer.

Exosphere: The upper most layer of the atmosphere is known as Exosphere. This layer has very thin air. Light gases like helium and hydrogen float into the space from here.

Air

Do you know that the air we take in while breathing is actually a mixture of many gases?Nitrogen and oxygen are two gases which make up the bulk of the atmosphere. Carbon dioxide, helium ,ozone,argon and hydrogen are found in lesser quantities. Apart from these gases.tiny dust particles are also present in the air.The pie chart gives you the percentage of different constituents of air.

Nitrogen is the most plentiful gas in the air.When we inhale.we take some amount of nitrogen into our lungs and exhale it.But plants need nitrogen for their survival. They can not take nitrogen directly from the air.Bacteria, that live in the soil and roots of some plants,take nitrogen from the air and roots of some plants,take nitrogen from the air and change its from so that plants can use it.

Oxygen is the second most plentiful gas in the air.Humans and animals take oxygen from the air as they breathe. Green plants produce oxygen during photosynthesis. In this way oxygen content in the air remains constant.if we cut trees then this balance gets disturbed.

Carbon dioxide is another important gas.Green plants use carbon dioxide to make their food and release oxygen. Humans or animals release carbon dioxide. The amount of carbon dioxide released by humans or animals seems to be equal to the amount used by the plants which make a perfect balance. However, the balance is upset by burning of fuels,such as coal and oil.They add billions of tons of carbon dioxide into the atmosphere each year.As a result,the increased volume of carbon dioxide is affecting the earth's weather and climate.

What is Environment?

In the class Ram asked his teacher," What is environment?" "Whatever you see in your surroundings," said the teacher.

Environment is our basic life support system. It provides the air we breath, the water we drink, the food we eat and the land where we live .

     How do human beings modify this natural environment?

The car fumes pollute the air, water is collected in a pot, food is served in vessels and land is used to build factories.

Human beings make cars,mills factories and manufacture containers. this is how human beings modify natural environment.

The place ,people things and nature that surround any living organism is called environment. It is a combination of natural and human made phenomena.While the natural environment refers to both biotic and abiotic conditions existing on the earth,human environment reveals the activities,creations and interaction among human beings.

NATURAL ENVIRONMENT

Land , water,air,plants and animals comprise the natural environment. You are familiar with the meaning of lithosphere, hydrosphere,atmosphere and biosphere from your previous class, Let us learn some more facts about these domains.

    Lithosphere is the solid crust or the hard top layer of the earth. It is made up of rocks and minerals and covered by a thin layer of soil.It is an irregular surface with various landforms such as mountains,plateaus,plains,Valle-ys,etc.Landforms are found over the continents and also on the ocean floors.

Lithosphere is the domain that provides us forests,grasslands for grazing , land for agriculture and human settlements.It is also a source of mineral wealth.

The domain of water is referred to as hydrosphere. It comprises various sources of water and different types of water bodies like rivers,lakes,seas,oceans, etc.

The atmosphere is the thin layer of air that surrounds the earth.the gravitational force of the earth holds the atmosphere around it .It protects us from the harmful rays and scorching heat of the sun .It consists of a number of gases,dust and water vapour.The changes in the atmosphere produce changes in the weather and climate.

Plant and animal kingdom together make biosphere or the living world. It is a narrow zone of the earth where land,water and air interact with each other to support life.

  5 June world environment day

                Barter System

What is ecosystem?

At an NCC camp that Ram's class was attending, John exclaimed, " What a heavy downpour. It reminds me of my home in Kerala.You should come and see how it pours and pours and pours over the lush green fields and coconut plantation." 

      Heera from Jaisalmer exclaimed," We get no rains.We see only ' kikar ' and sand, as far as the eyes can see," " But you also find camels", said Ram.

      Heera says,"Not just camels.If you visit our desert,you will see snakes, lizards and many insects too."

      Ram wondered," Why do the animals, the vegetation and the way people live vary from place to place ? Are they all related to each other?"

     "Oh yes, very much so", the teacher replied.

    All plants animals and human beings depend on their immediate surroundings. Often they are also interdependent on each other. This relation between the organisms and their surroundings from an ecosystem.

There could be an ecosystem of large rain forest, grassland, desert, mountains,lake,river,ocean and even a small pond.

Ecosystem: It is a system formed by the interaction of all living organisms with each other and with the physical and chemical factors of the environment in which the live ,all linked by transfer off energy and material.

           A Ponds Ecosystem

Inside Our Earth

              Interior of the earth

The uppermost layer over the earth's surface is called the crust . It is the thinnest of all the layers.It is about 35 Km.on the continental masses and only 5 Km. on the ocean floors.

The main mineral Constituents of the continental mass are silica and alumina.It is thus called sial { Si - silica and Al - Alumina }

The oceanic crust mainly consists of silica and magnesium , it is therefore called Sima { Si - silica and Ma - magnesium } just beneath the crust is the mantle which extends up to a depth of 2900 Km.below the crust.

The innermost layer is the core with a radius of about 3500 Km .

It is mainly made up of nickel and Iron and is called nife { ni - nickle and fe - ferros that is Iron}

{ The deepest mine in the world is  South Africa In search for oil engineers have dug a hole about 6000 Km deep.}

                 

          Rocks and Minerals

The earth's crust is made up of various types of rocks.Any natural mass of mineral matter that makes up the earths crust is called a rock.Rocks can be of diffrent colour , size and texture.

There are three major types of rocks: igneous rocks, sedimentary  rocks{Ex- sandstone is made from grains of sand.these rocks may also contain fossils of plants,animals and other micro-organisms that once lived on them} and metamorphic rocks{Ex- clay changes into slate and limestone into marble}.

When the molten magma cools , it becomes solid. Rocks thus formed are called igneous rocks. They are also called primary rocks . There are two types of igneous rocks: intrusive rocks { Ex- Granite }and extrusive rocks{ Ex- Basalt.The Deccan plateau is made up of basalt rocks } .

Can you imagine lava coming out from the volcanoes? Lava is actually fiery red molten magma coming out from the interior of the earth on its surface.When this molten lava comes on the earth's surface, it rapidly cools down and becomes solid .Rocks formed in such a way on the crust are called Extrusive igneous rocks.Sometimes the molten magma cools down deep inside the earth's crust. Solid rocks so formed are called intrusive igneous rocks.

You will be surprised to know that one type of rock changes to another type under certain conditions in a cyclic manner. This process of transformation of the rock from one to another is known as the rock cycle . When the molten magma cools; it solidifies to become igneous rock.These igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks.When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks.The metamorphic rocks which are still under great heat and pressure melt down to form molten magma.

This molten magma again can cool down and solidify into igneous rock.