Pythagoras Theorem Statement

Pythagoras theorem states that “In a right-angled triangle,  the square of the hypotenuse side is equal to the sum of squares of the other two sides“. The sides of this triangle have been named as Perpendicular, Base and Hypotenuse. Here, the hypotenuse is the longest side, as it is opposite to the angle 90°. The sides of a right triangle (say a, b and c) which have positive integer values, when squared, are put into an equation, also called a Pythagorean triple.

Pythagoras Theorem Formula

Consider the triangle given above:

Where “a” is the perpendicular,

“b” is the base,

“c” is the hypotenuse.

According to the definition, the Pythagoras Theorem formula is given as:

Hypotenuse2 = Perpendicular2 + Base2c2 = a2 + b2

The side opposite to the right angle (90°)  is the longest side (known as Hypotenuse) because the side opposite to the greatest angle is the longest.

Pythagoras Theorem Proof

Given: A right-angled triangle ABC, right-angled at B.

To Prove- AC² = AB² + BC²

Construction: Draw a perpendicular BD meeting AC at D.

Proof:

We know, △ADB ~ △ABC

Therefore, 

 (corresponding sides of similar triangles)

Or, AB² = AD × AC ……………………………..……..(1)

Also, △BDC ~△ABC

Therefore,

(corresponding sides of similar triangles)

Or, BC²= CD × AC ……………………………………..(2)

Adding the equations (1) and (2) we get,

AB² + BC² = AD × AC + CD × AC

AB² + BC² = AC (AD + CD)

Since, AD + CD = AC

Therefore, AC² = AB² + BC²

Hence, the Pythagorean theorem is proved.

Applications of Pythagoras Theorem

• To know if the triangle is a right-angled triangle or not.
• In a right-angled triangle, we can calculate the length of any side if the other two sides are given.
• To find the diagonal of a square.

Useful For

Pythagoras theorem is useful to find the sides of a right-angled triangle. If we know the two sides of a right triangle, then we can find the third side.

Pythagorean Theorem Problems

Problem 1: The sides of a triangle are 5, 12 & 13 units. Check if it has a right angle or not.

Solution: From Pythagoras Theorem, we have;

Perpendicular² + Base² = Hypotenuse²

Let,

Perpendicular = 12 units

Base = 5 units

Hypotenuse = 13 units {since it is the longest side measure}

12² + 5² = 13²

⇒ 144 + 25 = 169

⇒ 169 = 169 

L.H.S. = R.H.S.

Therefore, the angle opposite to the 13 units side will be a right angle.

Problem 2: Given the side of a square to be 4 cm. Find the length of the diagonal.

Solution- Given;

Sides of a square = 4 cm

To Find- The length of diagonal ac.

Consider triangle abc (or can also be acd)

(ab)² +(bc)² = (ac)²

(4)² +(4)²= (ac)²

16 + 16 = (ac)²

32 = (ac)²

(ac)² = 32

ac = 4√2.

Thus, the length of the diagonal is 4√2 cm.

Probability is defined as the likelihood or chance that an event will occur. It is defined as the
numerical method of measuring uncertainty involved in a situation.

To understand and measure
the chance, we perform the experiments like tossing a coin, rolling a die and spinning the
spinner etc.

Terms related to Probability:

 Sample space: It is the set of all possible outcomes in an experiment.
 Trial: An action which results in one or several outcomes.
 Experiment: An experiment is defined as an action or process that results in well defined outcomes.
 Event: The collection of some outcomes of the experiment.

Experimental Probability:
 The fraction of times event E is expected to occur.
 The estimated probability ≅ empirical probability for large number of trials.
The empirical probability P(E) of an event E is given as:
P(E) = (Number of trials in which event E has occurred)/(Total number of trials)

Example

If we throw a dice then what is the probability that we will get a 5?

Solution

Favourable outcome = 1 (there is only one possibility of getting 5)

Total no. of possible outcomes = 6 (total six numbers are there on a dice)

Probability of getting 5 = 1/6

Triangle

Triangle is a closed curve made up of three line segments. It has three vertices, sides and angles.

Here, in ∆ABC,

• AB, BC and CA are the three sides.
• A, B and C are three vertices.
• ∠A, ∠B and ∠C are the three angles.

Types of Triangle on the basis of sides

Types of Triangle on the basis of angles

Medians of a Triangle

Median is the line segment which made by joining any vertex of the triangle with the midpoint of its opposite side. Median divides the side into two equal parts.

Every triangle has three medians like AE, CD and BF in the above triangle.

The point where all the three medians intersect each other is called Centroid.

Altitudes of a Triangle

Altitude is the line segment made by joining the vertex and the perpendicular to the opposite side. Altitude is the height if we take the opposite side as the base.

• The altitude form angle of 90°.
• There are three altitudes possible in a triangle.
• The point of intersection of all the three altitudes is called Orthocenter.

The Exterior Angle of a Triangle

If we extend any side of the triangle then we get an exterior angle.

• An exterior angle must form a linear pair with one of the interior angles of the triangle.
• There are only two exterior angles possible at each of the vertices.

Here ∠4 and ∠5 are the exterior angles of the vertex but ∠6 is not the exterior angle as it is not adjacent to any of the interior angles of the triangle.

Exterior Angle Property of the Triangle

An Exterior angle of a triangle will always be equal to the sum of the two opposite interior angles of the triangle.

Here, ∠d = ∠a + ∠b

This is called the Exterior angle property of a triangle.

Example

Find the value of “x”.

Solution

x is the exterior angle of the triangle and the two given angles are the opposite interior angles.

Hence,

x = 64°+ 45°

x = 109°

Angle Sum Property of a Triangle

This property says that the sum of all the interior angles of a triangle is 180°.

Example

Find the value of x and y in the given triangle.

Solution

x + 58° = 180° (linear pair)

x = 180° – 58°

x = 122°

We can find the value of y by two properties-

1. Angle sum property

60° + 58° + y = 180°

y = 180°- (60° + 58)

y = 62°

2. Exterior angle property

x = 60°+ y

122° = 60° + y

y = 122° – 60°

y = 62°

Two Special Triangles

1. Equilateral Triangle

It is a triangle in which all the three sides and angles are equal.

2. Isosceles Triangle

It is a triangle in which two sides are equal and the base angles opposite to the equal sides are also equal.

Sum of the length of the two sides of a triangle

Sum of the length of the two sides of a triangle will always be greater than the third side, whether it is an equilateral, isosceles or scalene triangle.

Example

Check whether it is possible to make a triangle using these measurements or not?

1. 3 cm, 4 cm, 7 cm

We have to check whether the sum of two sides is greater than the third side or not.

4 + 7 = 11

3 + 7 = 10

3 + 4 =7

Here the sum of the two sides is equal to the third side so the triangle is not possible with these measurements.

2. 2 cm, 5 cm, 6 cm

2 + 5 = 7

6 + 5 =11

6 + 2 = 8

Here the sum of the two sides is greater than the third side so the triangle could be made with these measurements.

Right Angled Triangle

A right-angled triangle is a triangle which has one of its angles as 90° and the side opposite to that angle is the largest leg of the triangle which is known as Hypotenuse .the other two sides are called Legs.

Pythagoras theorem

In a right angle triangle,

(Hypotenuse)² = (base)² + (height)²

The reverse of Pythagoras theorem is also applicable, i.e. if the Pythagoras property holds in a triangle then it must be a right-angled triangle.

Example

Find the value of x in the given triangle if the hypotenuse is 5 cm and height is 4 cm.

Solution

Given:

Hypotenuse = 5 cm

Height = 4 cm

Base = x cm

(Hypotenuse)² = (base)² + (height)²

5² = x² + 4²

x² = 5² – 4²

x² = 25 – 16

x = 9

x = 3 cm

Revision Notes on Weather, Climate and Adaptations of Animals to Climate

Weather

The weather of a place can be defined as the measure of its daily atmospheric conditions such as humidity, temperature, lightning events, rainfall Storms, snow and so on.

Different elements of weather are:

• Rainfall
• Temperature
• Humidity
• Snowfall
• Storms
• Winds etc.

Figure 1: Different types of Weather

A weather report generally contains the information about the weather of the day.

The government has a special department called the Meteorological Department that predict the weather of a place and prepare the weather report.

The weather report is generally published in newspapers, radio and television.

The weather forecast is important for people because many of our day-to-day activities are based on weather conditions. For Example, we can check the possibility of rainfall on a particular day and carry an umbrella with us accordingly.

Figure 2: Weather Forecast

The weather of a place is never constant. It can alter every day or even every hour. For instance, the weather might be sunny in the morning in an area but really in the evening.

The weather report of a place always includes the minimum and maximum temperatures of the day which are measured using a minimum-maximum thermometer. The minimum temperature can be experienced in the morning time while the maximum temperature is experienced in the afternoon.

To measure the rainfall of a place an instrument called the Rain Gauge is used. The rain gauge collects the rainwater of origin and has a measuring scale which determines the quantity of rainfall of that place.

Figure 3: Rain Gauge

How do changes in weather occur?

Any change in the weather of a place on the earth is because of the Sun which radiates large amounts of heat and light energy on the earth. The formation of winds, the phenomena of rainfall and the change in seasons, all occur because of the Sun.

Why days are shorter in the winter season?

• We know that the Earth spins on an axis around the sun.
• Hence, the amount of sunlight a place receives various throughout the year as its position with respect to the sun changes because of the rotation of the Earth.
• This also leads to change in the seasons of a place.
• In the summer season, the position of the place is closer to the sun and hence it receives sunlight for longer hours while in the winter season the position of a place is farther to the sun and hence, it receives sunlight for shorter hours.

Figure 4: Change in Seasons

Climate

• The climate of a place can be defined as the prevailing weather conditions of the place for a long period of time, for example, 25 years.
• For Example, the temperature of Rajasthan is generally high throughout the year and it does not receive much rainfall so we can say that Rajasthan is a hot and dry place.

Figure 5: Different Climates on Earth

Climate and Adaptation

• The climate of a place can affect the living organisms of that area.
• The animals living in a particular region adapt themselves so that they can survive the weather conditions of that place.
• The features and habits of the animals start to change as per the climate of the place.

Polar Region

Figure 6: The polar region on the earth

• The area of the earth that surrounds the North Pole and the South Pole is called the Polar Region.
• The climate of the polar region is extremely cold throughout the year and receives heavy snow.
• The sun does not rise for 6 months of the year in the polar region and then It stays up for the next 6 months.
• The temperature in the polar region can be as low as – 37^°C.
• Most common animals found in these regions are polar bears and penguins. Other animals that can be found in polar areas are fishes, birds, oxen, musk, reindeers, fox, whales and seals.
• They have adapted themselves so that they can survive easily in these places. 

Figure 7: Animals in Polar Region

The Polar Bear

• The white fur of the polar bear makes it easier for them to hide in the snow and therefore save them from predators.
• In the same way, it makes it easier for them to catch their prey.
• The polar bears have two layers of thick fur on them so that they can survive extremely cold conditions.
• The polar bears move slowly and rest a lot so that they do not get overheated because of their thick fur.
• The polar bears often swim on warm days to keep themselves cool.
• The paws of the polar bear are large and wide so that it can swim as well as walk easily in the snow.
• The polar bear can swim underwater as well because it can keep its nostrils closed for a long time.
• The strong sense of smell of polar bears makes it possible to locate its prey during such harsh weathers.

Figure 8: Adaptation of Polar Bear

The Penguins

• The penguins are also white in colour so that they can hide in the snow.
• They have thick skin with large fat content in their body so that they can survive the cold weather easily.
• The Penguins generally live in a crowd or nest closely so that they can stay warm.
• The Penguins have webbed feet which allow them to swim.

Figure 9: Adaptation of Penguin

Migratory Birds in the Polar Region

• The birds in order to protect themselves from cold weather of the winters in the polar region often migrate from these areas to warmer places.
• They then return back after the winter season.
• For example, The Siberian crane migrates to India in Rajasthan, Haryana and some North East regions during the winter season in Siberia.
• These birds that migrate to different places during a change in weather are often called migratory birds.
• They can travel used instances of 15000 km to protect themselves from the extremely cold environment.
• Such birds migrate to the same places every year.
• The migratory birds fly very high so that the heat generated by the flight wings can be disposed of in the cold conditions.
• The migratory birds have a sense of direction so that they can travel to the same place every time.
• The migratory birds also use landmarks or follow the direction of the sun and stars to migrate.
• Some birds also use the magnetic field of the earth and find direction.
• Apart from birds, fishes, insects and mammals also migrate.

Figure 10: The Siberian Crane

Tropical Rainforests

Figure 11: The tropical region on earth

• The tropical regions on the earth are the regions which are close to the equator and hence receive more amount of sunlight during the year.
• Because of this, these areas have a hot climate.
• The temperature in tropical regions can be as high as 40^o C and can drop until 15 ^o C only.
• The length of the day and night are almost equal in these regions.
• However, there is a lot of rainfall and so the tropical rainforests are found in this region.
• The Tropical rainforests are home to a wide variety of vegetation and animals.
• Due to large habitation, the animals often compete for food in these regions.
• Many animals have adapted themselves so that they can live on the trees and find their food easily. The skin colour of these animals is generally similar to that of the surroundings so that they can catch their prey easily and protect themselves from the predators. Also, many of these animals have a good eyesight and better sense of hearing.

Different animals found in the tropical rainforests and their features:

Animals	Adaptation
The red-eyed frog	It has a sticky feat so that it can climb up on the trees easily.	Figure 12: The red-eyed frog
The monkeys	They have long tails so that they can climb the trees easily. Even their hands and feet have a structure that helps them in holding the branches of the trees easily.	Figure 13: Monkey in Tropical Rainforest
Toucan Birds	The Toucan birds adapt themselves so that they can find food easily. The Toucan bird has a large and long beak with which it can reach the food that is found on weaker branches as well.	Figure 14: Toucan Bird
Lions and Tigers	They have thick skin, sharp eyesight and sensitive hearing.	Figure 15: Tiger in Tropical Rainforest
The lion-tailed macaque (beard ape)	The beard ape lives generally on the trees in the tropical forest because it can find its food easily on them such as insects, seeds, fruits, leaves, flowers and stems. The beard ape also has a silver-white mane that starts from its head to its cheek.	Figure 16: The lion-tailed macaque (beard ape)
Elephants	The elephant found in the tropical rainforest also have adapted themselves according to the climate. Its huge trunk gives it a nice sense of smell and helps in picking the food easily. The elephant also eats the bark of the trees. The tusks or large teeth of elephant allow it to clear the bark of the trees. The large ears of the elephant allow it to hear sensitive sounds that make it easier for it to protect itself from predators. The ears also protect the elephant from the hot and humid climate of the rainforests.	Figure 17: Elephant in Tropical Rainforest

Importance of Soil

• Soil allows the growth of plants. It supplies water and nutrients that are required in the growth of plants.
• The soil is the main part of agriculture. Different types of soils support different kinds of crops. Without agriculture, food, shelter and clothing are not possible.
• Many microorganisms live in the soil.
• Underground water is used for various purposes.

Figure 1: Importance of Soil

What pollutes the soil?

• Dumping non-biodegradable substances such as plastic bags and polythene causes soil pollution.
• Waste products from industries which contain chemicals can affect the soil adversely.
• Excess use of fertilizers and pesticides pollute the soil and decrease its fertility.

Therefore, before dumping anything waste into the soil it must be treated properly. Pesticides and fertilizers should be used in minimum quantity. Lastly, materials like plastic should be banned as we pollute the soil and affect the living organisms as well.

Figure 2: What Causes Soil Pollution?

Soil Profile

The soil consists of distinct layers which are also called Horizons of the Soil.

The Soil Profile is a vertical section of the soil which depicts all the layers of the soil. The layers of the soil can be seen if we dig deep through it like while creating a well or while laying the foundation of a building.

• Humus – The decaying matter in the soil is called Humus.
• Weathering – Soil is formed when rocks break down. This process is also called Weathering. The weathering of rocks takes place because of rains, flowing water, winds, temperature and climatic conditions of a place.
• Parent Rock – The nature of the soil that is its texture and availability of minerals depends upon the rock from which it is formed. This rock is often called as the Parent Rock.

Figure 3: Soil Profile

Layers of the Soil

Horizon A

• This layer is also called the topsoil. It is visible to us.
• It contains large amounts of humus and minerals which makes it dark in colour.
• The soil is rich in nutrients because of the presence of humus.
• The topsoil has a soft texture and can retain water easily. That is why plants roots grow in the topsoil region.
• The topsoil is a home to many living organisms as well like insects, worms, beetles, rodents and moles.

Horizon B or the Middle Layer

• It is the next layer of the soil which does not contain much humus.
• The minerals are found in large quantities in this layer.
• This layer has a hard texture, light colour and is more compact than the topsoil.

Horizon C or Third Layer

• The third layer of the soil consists of small rocks with cracks in them. These rocks are partly weathered.

Bedrock

• The last layer of the soil is called the Bedrock.
• It contains large pieces of rocks that are not weathered or exposed to any winds or water.
• Bedrock cannot be dug with the help of a spade. It is very hard in texture.

How is Soil Formed?

We know that soil is formed from weathering of the parent rock and the texture of the soil depends upon the parent rocks only. This process takes time, maybe a hundred years, and then the fine soil is formed.

• In the first stage of soil formation, the soil is generally non-porous in nature. Then it slowly turns into soil having air and water in the pores.
• We can define soil as a mixture of rock particles and humus. Based on the size of the particles and the textures of the soil it can be divided into various types.

Figure 4: Formation of Soil

Types of Soil

Figure 5: Types of Soil

Sandy Soil

• Sandy soil has big particles that have large spaces between them.
• The spaces between these particles are filled with air. Hence, sandy soils are called well-aerated soils.
• Because of large spaces, water can easily penetrate through the particles of sand. Sandy soils, however, cannot hold water.
• Hence, sandy soils are light aerated and dry in nature.
• Sandy soils lack much nutrients hence do not support the diverse growth of plants.

Clayey Soil

• It consists of fine particles which have less space between them.
• Since there is not much space between the particles clayey soils are not well-aerated like sandy soils.
• The tiny gaps between the particles although allow absorption of water in the clayey soils easily
• They are able to hold water hence are suitable for the growth of different kinds of plants.

Loamy Soils

• Loamy soil contains a similar amount of large and small particles in them.
• They are combination of sandy, clayey and silty soil.
• They also contain humus.
• They can hold water in appropriate amounts and therefore support the growth of plants.
• They are also called Agricultural Soils because of their fertility and appropriate texture.
• They contain good amounts of calcium and have a high pH level.

Silt Soil

• The silt soil particles are smaller than that of sandy soils but larger than clayey soils.
• Silt soil can hold water to some extent because of its fine quality.
• They are generally found near the water bodies like river banks and lakes.
• They are rich in nutrients, highly fertile and hence are suitable for agriculture.
• They are often mixed with other soils to improve the fertility of the soil. 

Figure 6: Particle Size in Sand, Silt and Clay

Properties of Soils

1. Percolation of water through the Soil

Percolation can be defined as the property of the soil by which it allows the flow of water through it. The rate at which water percolates or moves through soils may vary in different kind of soils. Some soils absorb water while others allow it to flow through them. The rate of percolation can be calculated by:

Figure 7: Percolation of Water

2. Moisture

Moisture is the amount of water that is present in the soil. Even a dry soil has some amount of moisture in the air. However, the clayey soil has the highest content of moisture.

Why air above farmland appears shimmering during the daytime?

We know that soil contains water. Due to sunlight, the water from the soil begins to evaporate and turns into water vapour. This water vapour when reflects the sunlight appears as if it is shining and hence the air above the soil makes the land look shimmery.

3. Absorption

Every soil has a water absorption capacity which depends upon how porous the soil is. Clayey and loamy soils are most porous hence can retain water in large quantities. That is why crops can grow over these soils. Sandy soils, on the other hand, do not absorb water and hence do not support much vegetation.

4. Texture

The texture is the size of particles of the soil. Different kinds of soils have a different texture.

5. Colour

Different soils have different colours as well. This is because of the minerals and nutrients present in the soil. For instance, some soils are black in colour because of the presence of humus and minerals while some soils are red in colour because they have iron in large quantities in them.

Figure 8: Soils have different Colors

6. pH of Soil

Soils can have different pH depending upon their acidic, basic or neutral nature. Based upon the pH different types of crops grow in the soil.

7. Air Content

Since soil is made up of particles of different sizes these particles can be loosely bound or tightly bound. The air often occupies the space in between these particles. This allows life to sustain in the soil such as microorganisms.

Figure 9: Different Properties of Soils

Soil and Crops

Different kinds of soils are found in different regions because of the following factors that decide the soil structure of that place:

• temperature
• humidity
• rainfall
• sunlight
• winds

The type of crops that will grow in the soil depends upon these factors as well as the properties of a soil.

Type of Soil	Crops Grown
Sandy	Potato, Lettuce, Corn, Peppers
Clayey	Sprouts, Broccoli, Kale, Beans, Cabbage
Loamy	Apples, Carrots, Tomatoes, Cucumber

What is soil erosion?

• When the top layer of soil gets removed it is called soil erosion.
• The soil erosion mainly occurs when the soil is left loose without vegetation or when deforestation occurs.
• In such a situation, strong winds and flowing water or rainwater takes away the topsoil and therefore decrease its quality.
• Also, this kills the organisms living inside the soil.
• The roots of the plants and trees keep the soil together and allow several microorganisms to grow and survive there. Therefore, it is always advised to plant more trees and avoid deforestation

What are Rocks?

Rocks are mineral aggregates with a combination of properties of all the mineral traces. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe rock types. Additionally, different classification systems exist for each major type of rock. There are different types of rocks existing in nature.

Rocks which are found in nature rarely show such simple characteristics and usually exhibit some variation in the set of properties as the measurement scale changes.

Types of RocksTypes of Rocks in India

Types of Rocks

There are three types of rocks:

• Igneous Rocks
• Sedimentary Rocks
• Metamorphic Rocks

Igneous Rock

Igneous rock is one of the three main rock types. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.

This magma can be derived from partial melts of existing rocks in either a planet’s mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition.

Types of Igneous Rock

Following are the two types of igneous rock:

1. Intrusive igneous rock: These rocks crystallize below the earth’s surface resulting in large crystals as the cooling takes place slowly. Diorite, granite, pegmatite are examples of intrusive igneous rocks.
2. Extrusive igneous rock: These rocks erupt onto the surface resulting in small crystals as the cooling takes place quickly. The cooling rate is for a few rocks is so quick that they form an amorphous glass. Basalt, tuff, pumice are examples of extrusive igneous rock.

Igneous Rock Examples

Basalt	Diorite
Granite	Mica and quartz

Sedimentary Rock

The sedimentary rocks are formed by the deposition and subsequent cementation of that material within bodies of water and at the surface of the earth. The process that causes various organic materials and minerals to settle in a place is termed as sedimentation.

The particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, the sediment was formed by weathering and erosion from the source area and then transported to the place of deposition by water, wind, ice, mass movement or glaciers, which are called agents of denudation. Sedimentation may also occur as minerals precipitate from water solution or shells of aquatic creatures settle out of suspension.

Types of Sedimentary Rock

Following are the three types of sedimentary rock:

1. Clastic sedimentary rocks: These rocks are formed from the mechanical weathering debris. Sandstone, siltstone are examples of clastic sedimentary rocks.
2. Chemical sedimentary rocks: These rocks are formed from the dissolved materials that precipitate from the solution. Iron ore, limestones are examples of chemical sedimentary rocks.
3. Organic sedimentary rocks: These rocks are formed from the accumulation of plant and animal debris. Coal, some dolomites are examples of organic sedimentary rocks.

Sedimentary Rock Examples

Halite	Limestone
Sandstone	Siltstone

Metamorphic Rocks

The metamorphic rocks make up a large part of the Earth’s crust and are classified by texture and by chemical and mineral assemblage. They may be formed simply by being deep beneath the Earth’s surface, subjected to high temperatures and the great pressure of the rock layers above it.

Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means “change in form”. The original rock is subjected to heat with temperatures greater than 150 to 200°C and pressure around 1500 bars, causing profound physical and/or chemical change.

Types of Metamorphic Rock

Following are the two types of metamorphic rock:

1. Foliated metamorphic rocks: These rocks are produced by the exposure to heat and pressure which makes them appear layered. Phyllite, gneiss are examples of foliated metamorphic rocks.
2. Non-foliated metamorphic rocks: These rocks don’t have layers. Marble, quartzite are examples of non-foliated metamorphic rocks.

Metamorphic Rock Examples

Marble	Quartzite
Slate	Phyllite

Types of Rocks in India

Following are the classification of rocks in India:

1. Rocks of the Archaean system: These rocks get this name as they are formed from the hot molten earth and are the oldest and primary rocks. Gneiss is an example and is found in Karnataka, Andhra Pradesh, Tamil Nadu, Madhya Pradesh, Orissa and some parts of Jharkhand and Rajasthan.
2. Rock of Dhawar system: These are formed from the erosion and sedimentation of the Archaean system and are the oldest sedimentary rocks. These are mainly found in Karnataka.
3. Rocks of Cuddapah system: These are formed from the erosion and sedimentation of Dhawar system. Sandstone, limestone and marble asbestos are the examples and are mainly found in Rajasthan.
4. Rocks of the Vindhyan system: These are formed from the silt of river valleys and shallow oceans. Red sandstone is an example and is mainly found in Madhya Pradesh.
5. Rocks of Gondwana system: These are formed from the depressions in the basins. Coal is an example and is mainly found in Madhya Pradesh.
6. Rocks of Deccan trap: These are formed from the volcanic eruption. Dolorite and basalt are examples and are mainly found in Maharashtra and parts of Gujarat, Tamil Nadu and Madhya Pradesh.
7. Rocks of Tertiary system: These rocks are found mainly in the Himalayan regions.
8. Rocks of the Quarternary system: These rocks are found in the plains of the Indus and Ganga.

What is Global Warming?

Earth absorbs about 75 % of the total solar energy reaching its surface thereby increasing its temperature. Some of this energy is radiated back into the atmosphere. The gases present in the atmosphere for example ozone, methane, carbon dioxide, water vapour and chlorofluorocarbons are called greenhouse gases, they absorb some heat thereby restricting the heat to escape our atmosphere. These gases add to the heating of the atmosphere and result in global warming.

In places where the temperature is low, we use glass covered areas known as a greenhouse to grow flowers, fruits, and vegetables. It is very interesting to know that even we live in a greenhouse, but the difference is that we are not covered by the glass but by the blanket of air called the atmosphere. It is this atmosphere which has kept the earth’s temperature constant for centuries and helped in the survival of life. Atmosphere traps the heat around the earth and keeps it warm. This is called as natural greenhouse effect because it maintains the temperature and sustains life.

In a greenhouse, the solar energy enters through the glass, warms the soil and atmosphere and helps in the growth of plants. In return, the soil and plants emit infrared radiation, which is partly absorbed and partly reflected by the glass. This mechanism traps the sun’s energy in the greenhouse. Similarly, we have carbon dioxide which absorbs heat (as they are transparent to sunlight but not to infrared heat radiation) and is the major contributor to the global warming.

Other than carbon dioxide we have methane, ozone, CFC’s and nitrous oxides forming a major part of greenhouse gases. These chemicals either occur naturally or are man-made. The use of these compounds should be reduced; otherwise, the average temperature of the earth will rise. This will result in melting of polar ice caps and flooding of the coastal areas. Increase in the global temperature also increases the incidence of diseases like dengue, malaria, yellow fever etc.

What is the Greenhouse Effect?

To understand the nature of the greenhouse effect on climate change which leads to global warming, we must first know what the greenhouse effect is.

When you enter a car that has been in the sun for quite some time, what is the first thing you notice? It is a lot hotter inside than it is outside. The sun’s rays (UV radiation, thermal radiation, visible light) enter the car through the glass panes and all the rays entering the car do not leave owing to the build up of gases inside the car and the refractive properties of the glass itself. The weaker thermal radiation does not completely leave the car. This eventually heats up the inside of the car.

The same thing happens in a greenhouse. The plants in a greenhouse require a warm temperature to grow. Have you ever seen a greenhouse? It is made almost entirely out of glass. The heat is retained and the plants thrive. The temperature inside a greenhouse is always higher than the temperature outside.

A typical greenhouse used to regulate the climate for plant growth

This is called the greenhouse effect. What happens when the greenhouse effect occurs on a large scale in the world itself? This is where greenhouse gases come in.

Let’s have a little back-story here. Other planets in our solar system are either extremely cold or really hot. It’s the only planet earth that has a climate which is mild enough to support life. This is because of the presence of a thin layer of naturally occurring greenhouse gases like carbon dioxide, methane gas, water vapour and nitrous oxide. These gases are part of our atmosphere. The atmosphere here plays the role of the glass pane like in the greenhouse. They let the sun’s rays inside but not all of it is reflected back. The greenhouse gases even facilitate the absorption of the heat thereby warming up the earth and not letting it become extremely cold like it otherwise should have been.

The Greenhouse Effect

Since the beginning of the 18th century, the concentration of these gases in the atmosphere has started rising gradually. Since then, CO₂ levels have risen around 40%. And why is this happening? Different human activities, mainly industrial, have led to the production of these gases; the most common being carbon dioxide. The unnatural presence of increased greenhouse gases has led to a more pronounced greenhouse effect which has altered the temperature of the earth, leading to a phenomenon termed ‘Global Warming’.

Climate Change Due To Global Warming

A universal consensus of climate scientists is that there has definitely been a rise in the global temperature over the past century. The phenomenon of Global Warming if continued unchecked will have profound implications.

One of the main effects of global warming will be the rise in sea and ocean levels. Currently, this is already occurring around us. Melting of glaciers and polar ice caps will contribute to the rise in water levels all over the world. Apart from this, fresh water sources will also reduce. According to scientific bodies like NASA, other consequences of global warming are ocean acidification, extreme weather events and other natural and societal impacts.

Projected change in annual average precipitation for the 21st century based on the SRES A1B emissions scenario, and simulated by the GFDL CM 2.1 model

So can we control or check this from happening? There are some like Josef Werne, an associate professor at the department of geology & planetary science at the University of Pittsburgh, who believes that we have already crossed the point of no return. All we can do now is to adapt to the changing environment and the rising sea and ocean levels. We can still lessen the severity of climate change by aggressively enforcing policies that require different bodies to lessen CO₂ levels in the atmosphere. Still, others are even more optimistic believing that strong international agreements and actions can save the planet and it’s changing atmosphere.

Projected impact of climate change on agricultural yields by the 2080s, compared to 2003 levels (Cline,2007)

Greenhouse Gases

Many chemical compounds in the atmosphere act as greenhouse gases. These gases allow sunlight (short wave radiation) to freely pass through the Earth’s atmosphere and heat the land and oceans. The warmed Earth releases this heat in the form of infrared light (long wave radiation), invisible to human eyes. Some infrared light released by the Earth passes through the atmosphere back into space. However, greenhouse gases will not let all the infrared light pass through the atmosphere. They absorb some and radiate it back down to the Earth. This phenomenon, called the greenhouse effect, is naturally occurring and keeps the Earth’s surface warm. It is vital to our survival on Earth. Without the greenhouse effect, the Earth’s average surface temperature would be about 60° Fahrenheit colder, and our current way of life would be impossible.

We know that several gases in the atmosphere can absorb heat. These greenhouse gases are produced both by natural processes and by human activities. The primary ones are:

• Carbon dioxide (CO₂)
• Methane (CH₄)
• Nitrous oxide (N₂O)

Industrial Gases, including hydrofluorocarbons, per fluorocarbons, and sulphur hexafluoride.

Greenhouse Gas Conc. Chart in ppm

Greenhouse Gases List

Greenhouse gas	How it’s produced	100-year global warming potential	Average lifetime in the atmosphere
Methane	Released during the production and transport of natural gas, coal, and oil. It also results from agricultural practices, livestock and decay of organic waste in municipal solid waste landfills.	21	12 years
Carbon Dioxide	Released primarily when fossil fuels like natural gas, coal, and oil are burnt. Burning of trees, wood, and waste also release carbon dioxide. Changes in land use also play a role. Soil degradation and deforestation add carbon dioxide to the atmosphere, while forest regrowth takes it out of the atmosphere.	1
Nitrous oxide	Emitted during industrial and agricultural activities as well as during combustion of solid waste and fossil fuels	310	114 years
Fluorinated gases	A group of gases that includes per fluorocarbons, hydrofluorocarbons, and sulphur hexafluoride, among other chemicals. These gases are released from a variety of commercial and industrial processes and household uses and do not occur naturally. Sometimes used as substitutes for ozone-depleting substances such as chlorofluorocarbons (CFCs).	Varies	Few weeks to thousands of years

Composition of the atmosphere

• The atmosphere is made up of different gases, water vapour and dust particles.
• The composition of the atmosphere is not static and it changes according to the time and place.

Gases of the atmosphere

The structure of the atmosphere is represented in a pictorial form below:

There are five layers in the structure of the atmosphere depending upon temperature. These layers are:

• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
• Exosphere

Troposphere

• It is considered as the lowest layer of Earth’s atmosphere.
• The troposphere starts at the surface of the earth and goes up to a height of 8 kms (poles) to 18 kms (equator). The main reason of higher height at the equator is due to presence of hot convection currents that push the gases upward.
• All kinds of weather changes occurs within this layer.
• This layer has water vapor and mature particles.
• Temperature decreases with increasing height of atmosphere at the rate of 1 degree Celsius for every 165 m of height. This is called Normal lapse rate.
• Tropopause, the transitional zone, separates Troposphere and Stratosphere.

Stratosphere

• It is the second layer of the atmosphere found above the troposphere.
• It extends up to a height of 50 km from the earth’s surface.
• This layer is very dry as it contains little water vapour.
• This layer provides some advantages for flight because it is above stormy weather and has steady, strong, horizontal winds.
• The ozone layer is found in this layer.
• The ozone layer absorbs UV rays and safeguards earth from harmful radiation.
• Stratopause separates Stratosphere and Mesosphere.

Mesosphere

• The Mesosphere is found above the stratosphere.
• It is the coldest of the atmospheric layers.
• The mesosphere starts at 50 km above the surface of Earth and goes up to 80 km.
• The temperature drops with altitude in this layer.
• By 80 km it reaches -100 degrees Celsius.
• Meteors burn up in this layer.
• The upper limit is called Mesopause which separates Mesosphere and Thermosphere.

Thermosphere

• This layer is found above Mesopause from 80 to 400 km.
• Radio waves that are transmitted from the earth are reflected by this layer.
• The temperature starts increasing again with increasing height in this layer.
• Aurora and satellites occur in this layer.

Ionosphere

• The lower Thermosphere is called the Ionosphere.
• The ionosphere consists of electrically charged particles known as ions.
• This layer is defined as the layer of the atmosphere of Earth that is ionized by cosmic and solar radiation.
• It is positioned between 80 and 400 km above the Mesopause.

Exosphere

• It is the outermost layer of the atmosphere.
• The zone where molecules and atoms escape into space is mentioned as the exosphere.
• It extends from the top of the thermosphere up to 10,000 km.

Frequently Asked Questions related to Structure of Atmosphere

What are 3 facts about the atmosphere?

The atmosphere layer closest to the earth is referred to as the troposphere. Beyond the troposphere are the stratosphere, the ozone layer, the mesosphere, and the thermosphere. The atmosphere is made up of 78% nitrogen, 21% oxygen, and smaller amounts of argon, carbon dioxide, helium, and neon.

Which is the coldest layer of the atmosphere?

The top of the mesosphere is the coldest area of the Earth’s atmosphere because temperature may locally decrease to as low as 100 K (-173°C).

Living organisms adapt to their moves and positions in response to the environmental changes for their protection or to their advantage. When an entity reacts to the changes in its surroundings, it is referred to as stimulus while the reaction to the stimulus is referred to as a response. Common stimuli are sound, light, air, heat, smell, taste, water and gravity.

Think of burning your finger of fracturing your bone without any pain sensation. It may certainly sound like a superpower or an ideal situation, however, when it comes to the standpoint of survival, it can be disastrous.

It is a characteristic behaviour of living entities to respond to stimuli with the intervention of the Nervous System. It is an organ system ascribed to send signals from the spinal cord and the brain throughout the body and then back from all the body parts to the brain. Neuron acts as the mediator and is the basic signalling unit of the Nervous system.

Pain is the body’s way of letting us know that something is not right. It can prevent further injuries or push us to seek medical attention. Moreover, all of this is possible because humans can respond and react to stimuli due to control and coordination among the various organs and organ systems.

Control and Coordination in simple multicellular organisms take place through only the Nervous system which coordinates activities of our body. It is the control system for all our actions, thinking, and behaviour.

Let us have a detailed look at the nervous system notes to explore what is the nervous system, and the different functions of the nervous system.

What is the Nervous System?

The nervous system or the neural system is a complex network of neurons specialized to carry messages. The complexity of the nervous system increases as we move towards higher animals.

For instance, cnidarians such as jellyfish have relatively simple nerve nets spread throughout their body. Crabs have a more complicated nervous system in the form of 2 nerve centers called dorsal ganglion and ventral ganglion.

As we move further up the ladder, higher organisms such as vertebrates have a developed brain. Moreover, it is one of the most complicated structures in the animal kingdom, containing billions of neurons, all intricately connected.

In the human body, the neural system integrates the activities of organs based on the stimuli, which the neurons detect and transmit. They transmit messages in the form of electrical impulses and convey messages to and from the sense organs. Thus, the nervous coordination involves the participation of the sense organs, nerves, spinal cord, and brain.

Human Nervous System

One of the most complex organ system to ever evolve, the human nervous system consists of two parts, namely:

1. Central Nervous System (consists of the brain and spinal cord)
2. Peripheral Nervous System (includes all the nerves of the body)

Central Nervous System

Central Nervous System (CNS) is often called the central processing unit of the body. It consists of the brain and the spinal cord.

Brain

The brain is one of the important, largest and central organ of the human nervous system. It is the control unit of the nervous system, which helps us in discovering new things, remembering and understanding, making decisions, and a lot more. It is enclosed within the skull, which provides frontal, lateral and dorsal protection. The human brain is composed of three major parts:

1. Forebrain: The anterior part of the brain, consists of Cerebrum, Hypothalamus and Thalamus.
2. Midbrain: The smaller and central part of the brainstem, consists of Tectum and Tegmentum.
3. Hindbrain: The central region of the brain, composed of Cerebellum, Medulla and Pons.

Spinal Cord

The spinal cord is a cylindrical bundle of nerve fibers and associated tissues enclosed within the spine and connect all parts of the body to the brain. It begins in continuation with the medulla and extends downwards. It is enclosed in a bony cage called vertebral column and surrounded by membranes called meninges. The spinal cord is concerned with spinal reflex actions and the conduction of nerve impulses to and from the brain.

Peripheral Nervous System

Peripheral Nervous System (PNS) is the lateral part of the nervous system that develops from the central nervous system which connects different parts of the body with the CNS. We carry out both voluntary and involuntary actions with the help of peripheral nerves.

PNS includes two types of nerve fibers:

1. Afferent nerve fibers – These are responsible for transmitting messages from tissues and organs to the CNS.
2. Efferent nerve-fibers – These are responsible for conveying messages from CNS to the corresponding peripheral organ.

Classification of the peripheral nervous system:

Somatic neural system (SNS): It is the neural system that controls the voluntary actions in the body by transmitting impulses from CNS to skeletal muscle cells. It consists of the somatic nerves.

Autonomic neural system (ANS): The autonomic neural system is involved in involuntary actions like regulation of physiological functions (digestion, respiration, salivation, etc.). It is a self-regulating system which conveys the impulses from the CNS to the smooth muscles and involuntary organs (heart, bladder and pupil). The autonomic neural system can be further divided into:

1. Sympathetic nervous system
2. Parasympathetic nervous system

Neuron

A Neuron is a structured and functional unit of the nervous system and unlike other cells, neurons are irregular in shape and able to conduct electrochemical signals. The different parts of a neuron are discussed below.

• Dendrite stretches out from the cell body of a neuron, and it is the shortest fibre in the cell body.
• Axon is the longest thread on the cell body of a neuron and has an insulating and protective sheath of myelin around it.
• Cell body consists of cytoplasm and nucleus.
• Synapse is the microscopic gap between a pair of adjacent neurons over which nerve impulses pass, when moving from one neuron to the other.

Nerves

Nerves are thread-like structures that emerge from the brain and spinal cord. It is responsible for carrying messages to all the parts of the body. There are three types of nerves. Some of these neurons can fire signals at speeds of over 119 m/s or above 428 km/h.

1. Sensory nerves send messages from all the senses to the brain.
2. Motor nerves carry messages from the brain to all the muscles.
3. Mixed nerves carry both sensory and motor nerves.