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.

Greenhouse gas and Global warming

Carbon dioxide released in the atmosphere creates a green house effect by trapping the heat radiated from the earth.It is therefore called a greenhouse gas and without it the earth would have been too cold to live in.

However, when its level in the atmosphere increases due to factory smoke or car fumes,the heat retained increases the temperature of the earth.This is called global warming. This rise in temperature causes the snow in coldest parts of the world to melt.As a result the sea level rises,causing floods in the coastal areas.

There may be drastic changes in the climate of a place leading to extinction of some plants and animals in the long run.

Major Land Forms

The landscape is being continuously worn away by two processes- weathering and erosion. Weathering is the breaking up of the rocks on the earth's surface. Erosion is the wearing away of the landscape by different agents like water,wind, and ice. The eroded material is carried away or transported by water,wind,etc.and eventually deposited. This process of erosion and deposition create different landforms on the surface of the earth.

Work of a River

The running water in the river erodes the landscape.When the river tumbles at steep angle over hard rocks or down a steep valley side it forms a waterfall.

As the river enters the plain it twists and turns forming large bends known as meanders. Due to continuous erosion and deposition along the sides of the meander,the ends of the meander loop come closer and closer.In due course of time the meander loop cuts off from the river and forms a cut - off lake,also called an ox-bow lake.

At times the river overflows its banks.This leads to the flooding of the neighbouring areas.As it floods,it deposits layers of fine soil and other material called sediments along its banks.This leads to the formation of a flat fertile floodplain. The raised banks are called levees.As the river approaches the sea,the speed of the flowing water decreases and the river begins to break up into a number of streams called distributaries.The river become so slow that it begins to deposit its load.Each distributary forms its own sediments form all the mouths forms a delta.

Waves of Sea Waves 

The erosion and deposition of the sea waves gives rise to coastal landforms. Seawaves continuously strike at the rocks.Cracks develop.Over time they become larger and wider .Thus ,hollow like caves are formed on the rocks.They are called sea caves. As these cavities become bigger and bigger only the roof of the caves remain,thus forming sea arches. Further, erosion breaks the roof and only walls are left.These wall like features are called stacks.

The steep rocky coast rising almost vertically above sea water is called sea cliff.

The sea waves deposit sediments along the shores forming beaches.

Work of Ice 

Glaciers are "rivers of ice"which too erode the landscape by bulldozing soil and stones ti expose the solid rock below.

Glaciers carve out deep hollows there .As the ice melts they get filled up with water and become beautiful lakes in the mountains.The material carried by the glacier such as rocks big and small,sand and silt gets deposited. These deposits form Glacial moraines.

                   A Glacier

Work of wind

Have you ever visited a desert?Try to collect some pictures of sand dunes.

     An active agent of erosion and deposition in the deserts is wind .In deserts you can see rocks in the shape of a mushroom,commonly called mushroom rocks.Winds erode the lower section of the rock more than the upper part. Therefore,such rocks have narrower base and wider top.when the wind blows,its lifts and transports sand from one place to another. When it stops blowing the sand falls and gets deposited in low hill-like structures. These are called sand dunes. When the grains of sand are very fine and light.the wind can carry it over very long distances. When such sand is deposited in large areas,it is called loess. Large deposits of loess is found in China.

                Sand dunes

Earthquake and Volcanoe

Endogenic forces sometimes produce slow movements.sudden movements like earthquaks and volcanoes cause mass destruction over the surface of thr earth.

A volcanoe is a vent { Opening } in the earth's crust through which molten material erupts suddenly.

                A Volcanoe

Similarly,when the Lithosphere plates move ,the surface of the earth vibrates.The vibrations can travel all round the earth.These vibrations are called earthquakes . The place in the crust where the movement starts is called the  focus . The place on the surface above the focus is called the epicentre . Vibrations travel outwards from the epicentre as waves.Greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away form the centre.

       Orgin of an Earthquake

Although earthquakes cannot be predicted, the impact can certainly be minimised if we are prepared before-hand.

    Some common earthquake prediction methods adopted locally by people include studying animal behavior; fish in the ponds get agitated,snakes come to the surface.

There are three types of earthquake waves 

Earthquake Preparedness

An earthquake is measured with a machine called a seismograph.The magnitude of the earthquake is measured on the Richter scale.An earthquake of 2.0 or less can be felt only a little. An earthquake over 5.0 can cause damage from things falling. A 6.0 or higher magnitude is considered very strong and 7.0 is classified as a major earthquake.

               A seismograph

 

          Earthquake images

Our Changing Earth

The lithosphere is broken into a number of plates known as the Lithospheric plates. You will be surprised to know that these plates move around very slowly- just a few millimeters each year. This is because of the movement of the molten magma inside the earth.The molten magma inside the earth moves in circular manner as shown in the activity.

      The movement of these plates causes changes on the surface of the earth. The earth movements are divided on the basis of the forces which cause them .The forces which act in the interior of the earth are called as Endogenic forces and the forces that work on the surface of the earth are called as Exogenic forces .

       Evolution of Landforms

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