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A comet is a celestial object made up of a head and a tail. Halley’s comet is one of the famous comets.

For long we have looked at the earth as a store house of resources. With this view we recklessly exploited the earth and are responsible to the destruction of forests, rivers, hills, fellow animals and even fellow humans. This resulted in the environmental crises such as global warming and poisoning of our soils, water and air.

But gradually we understand that the earthly resources are not infinite but finite and the environmental system is a closed one. So we should not use the natural resources indiscriminately.

If a man has to survive, he must derive something from the nature. The exploitation of minimum resources from the natural environment to fulfil the basic needs of human society would cause disequilibrium of some sort in the ecological balance resulting into environmental degradation and pollution. We should always use the natural resources in such a way that they are always at available in a desired quantity and quality.

A cluster of millions of stars is called Akash Ganga.

In the decades of 1970s there emerged a concern about the fear of depletion of natural resources because of irrational and rapacious utilization of natural resources. This serious concern arises from the fact-rapid rate of rapacious exploitation of natural resources and modern production processes and advanced technologies. Thus the exploitation of natural resources has threatened the stability and survival of natural ecosystems and existence of several plant and animal species.

Hence today more than any other time we need to build a new understanding of the earth, how it works and what we do on it and what we do with each other

Countries which have much east-west extension will have a number of standard times.

Ex: Russia.

We do not feel the heat and light of the stars because they are very far away from us.

1. A larger group of stars is called a galaxy.

2. ‘Big bang’ was happened some IB.7 billion years ago.

3. Scientists contemplated that there are millions of galaxies in the universe.

4. The end of the universe would be after several billions of years.

Correct option is C) Venus.

Universe started some 13.7 billion years ago.

Mercury and Venus do not have any satellites.

A satellite is an object that orbits another object. They are natural and man-made. Moon is a natural satellite of the Earth. Satellites are used for many purposes. They are weather satellites, communication satellites, navigation satellites, astronomy satellites and many other kinds. 

1. They are used for communication purposes. 

2. Carry instruments or passengers to perform experiments in space. 

3. For weather forecasting system. 

4. For global positioning system. (GPS).

• For thousands of years humans have been looking into the sky trying to understand objects that shine there. 
• Initially, people thought that earth was firm and stationary and all others went round it.
• They also thought that the earth, the stars and the sun have been like this forever and will be like this forever without any change.

• More than any other animal human beings have been trying to make the earth a better place to live in. 
• Trying to change ourselves and our surroundings we have entered into conflict with other inhabitants of the earth. 
• For long we’ve been exploiting the earth for its resources.
• The reckless exploitation of the earth resulted in environmental crises such as global warming and poisoning of our soils, water and air. 
• Thus we can say man himself is responsible for environmental crises.

The percentage of Earth Crust in the volume of the earth 1%

The world is divided into 24 time zones. Number of longitudes in each one are 15.

(C) 15° of longitudes

The earth is made up of three main layers. 

A) Crust:

1. The outer part of the earth on which we live is called the crust. 

2. While the earth was boiling in a molten form the lighter particles cooled at the top and formed the layer of crust. 

3. The curst mostly consists of various kinds of rocks. 

4. This layer goes up to a depth of 30 to 100 kms.

B) Mantle: 

1. While the earth was boiling in a molten form the less heavier particles settled in the middle and formed the mantle. 

2. The upper part of the mantle is a pliable layer over which the crust floats. 

3. This layer consists mainly of chemicals called silicates.

4. It exists at the depths from 100 kms to 2900 kms. 

C) Core: 

1. While the earth was boiling in a molten form the heaviest substances formed core. 

2. It is composed of dense and heavy substances like Iron and Nickel. 

3. It exists at the depths from 2,900 kms to 6,376 kms. 

4. It can be divided into two sub-layers.

a) Outer core : 

This layer is composed of liquid metallic material like nickel and iron. It is 2,900 – 5,100 kms in thickness. 

b) Inner core : 

The solid inner core is made up of iron compounds and heavy substances like gold. It is 5,100 – 6,376 kms in thickness.

The network of latitudes and longitudes is grid

Difference between Local and Standard time:

Example:

If the IST is 12.00 noon, the local of Mumbai is 39 minutes – IST = 11.21 minutes a.m. Since Mumbai is on 72°82′ east longitudes, it is 9°45′ behind the 82°30′. Thus the local time of Mumbai is 9.45 x 4 = 38 minutes.

If every state follows its local time, a lot of serious problems would rise. Some of them are being discussed hereunder.

• At the time of national calamities and disasters, it is very difficult for the national government to make necessary emergency announcement.
• At the time of wars and national emergency it is very difficult for the national government to alert all the defensive forces stationed in all the state capitals and the naval forces of all the coastal states. 
• It is very difficult for Televisions and Radios to follow a single schedule to broadcast their programmes. 
• Railways faces a difficult problem in preparing a timetable for its trains that travel through many states.

Answer is (D) Europe

The number of longitudes in a time zone 15

• It takes 4 minutes for the sun’s position to move 1° of longitude. 
• This means that the time is different for each degree of longitude. 
• This can cause a lot of confusion.
• Therefore to end up this confusion the world is divided into 24 time zones. 
• The width of each time zone is 15° of longitude.
• This means the difference between one time zone and the next is 1 hour.
•  As you go from Greenwich meridian, you add time; as you go west of the Greenwich meridian you subtract time.

If every state follows its local time, the following problems will arise :

• People travelling to different states would have to change their clocks too often.
• There would be confusion and chaos in the timings of railways, airlines, buses etc. 
• The schedules of television shows, live shows and games, news etc. would be disrupted.

(C) Google Earth

• Longitudes are imaginary lines connecting North and South ’Poles. 
• Longitudes are semi-circles. 
• Longitudes are also called meridians because when the sun is overhead on a longitude at the time on that longitude it is noon (meridianus).
• There are 360 longitudes in total. 
• The longitudes from 0° to 180° to the east are called eastern longitudes. 
• The longitudes from 0° to 180° to the west are called western longitudes. 
• 0° meridian is called the Prime meridian or Greenwich meridian. 
• Longitudes are also expressed in degrees (°), minutes (‘) and seconds (“).

a) India, Arabia, Malaysia, East Indies. 

b) The present Europe continent was formed from Laurensia block.

• Latitudes are imaginary lines drawn around the earth. 
• The word ‘latitude’ comes to us from the Latin word ‘iatitudo’ meaning width. 
• Latitudes are also called parallels because they are parallel to each other. 
• Latitudes are circles. 
• Latitudes are expressed in degrees (°), minutes (‘) and seconds (“). 
• Latitude values range from 0° t* 90° North (the North Pole) and 90° South (the South Pole).
• Thus there are 180° main latitudes (not counting the equator) 
• Equator, the 0° latitude is the largest among all the latitudes. 
• Latitudes are used together with the longitudes to locate a place on the earth. 
• Latitudes are used to locate the climatic zones on the earth.

Wagener proposed continental drift theory.

(A) On the floor

Big Bang: The single large explosion that created the universe.

The massive supercontinent Pangaea, which existed 220 million years ago and then breaking apart into several large sections such as Laurentia and Gondwana.

• In 1912 Alfred Wegener propounded the theory of continental drift to describe the present arrangement of continents and ocean basins.
• He postulated a massive super continent Pangaea that existed 220 million years ago. 
• Pangaea, the hypothetical continent, from which present continents originated by the drift from Mesozoic era to the present. 

Wegener hypothesized that the super continent of Pangaea broke up to from : 

a) Laurensia – consisting of present North America, Greenland and all of Eurasia north of Indian subcontinent and 

b) Gondwana land – consisting of present South America, Africa, Madagascar, Arabia, India, Malaysia, East Indies, Australia and Antarctica.

• These two blocks were separated by a long shallow inland sea called Tethys sea. 
• It took millions of years for the continents to reach the present shapes and positions on the globe.
• Even today many of the continents are moving very slowly pushing each other.

• Different kinds of gases including water vapour formed the atmosphere on earth. 
• Most of these gases were such that life as we know it today could not survive on it.
• Because it did not have oxygen necessary for life to survive. It took a long time for the air to develop. 
• Then life appeared on oceans first.
• It slowly evolved into diverse forms – plants, animals and human beings.

The shapes and positions of the continents may seem fixed at the time scale of human experience. But on old earth continents have moved, collided, merged and then been torn apart again.

Mountains have risen and been razed to the ground, oceans have formed and dried up. Valleys have been carved and so during the course of earth’s eventful history. Alfred Wegener’s theory of Continental drift proves the same idea.

Thus the shapes and positions of the continents are not fixed and permanent.

1. The continents took millions of years to reach their present shape and positions on the globe.

2. We can find the latitudinal and longitudinal information of a place in a well-produced atlas or online using Google Earth. 

3. With the help of the grid – a network of latitudes and longitudes we can locate places on the globe and learn much about them. 

4. While latitudes are horizontal circles, the longitudes are semi-circles connecting the north pole and the south pole. 

5. There are 180 latitudes and 360 longitudes. The standard time of a country is the time of the meridian that passes through the center of that country. 

6. The time difference between the eastern and western extremes of the country is two hours.

By observing the maps of the world from 220 million years ago up to the present world, we can find the following continents look as if they are two pieces of jigsaw puzzle. 

They are : 

1) North America and North West Africa. 

2) South America and Western Africa. 

3) Nothern Africa and Eurasia. 

4) Eastern Africa and India. 

5) South Eastern Africa and Antarctica. 

6) Antarctica and Australia.

2. Australia is moving in eastern direction.

3. India is moving in northern direction.

(B) 6000 kms

Answer is (B) 0°S

(A) 23\(\frac{1}{2}\)° South latitude

In the olden days, people in the northern hemisphere determined the directions with the help of the north star. With the help of the north star, they determine the north direction. It always remains in the same direction in the sky. It is also called the pole star.

The anti meridian is the meridian of longitude opposite the Prime-Meridian.

a) Kanyakumari : 77°36′ E longitude and 8°35′ N latitude 

b) Imphal : 93°58′ E longitude and 24°44′ N latitude 

c) Jaisalmer : 26°55′ N latitude and 70°54′ E longitude 

d) Pune : 18°32′ N latitude and 73°52’E longitude 

e) Patna : 27°34′ N latitude and 81°46′ E longitude

(i) (B) Alahabad

(ii) (A) Gujarath

(B) 82\(\frac{1}{2}\)° E

а) Latitudes are called ‘parallels’, 

b) Longitudes are called ‘meridians’.

The largest latitude is Equator

Today people are curious to know about the secrets of the distant stars and galaxies and the beginning of the universe a) to understand the stars that shine there. 

b) to understand the sun, the moon and the planets which keep moving across the sky. 

c) to understand what are these and in what way they are related to us and how they affect us. 

d) to know how they move and work. e) to know whether there is any life on any other planet.

We can locate places on the earth with the help of grid

a) Difference between Local and Standard time :

Example: If the 1ST is 12.00 noon, the local of Mumbai is 39 minutes – 1ST = 11.21 minutes a.m. 

Since Mumbai is on 72°82′ east longitudes, it is 9°45′ behind the 82°30′. Thus the local time of Mumbai is 9.45 x 4 = 38 minutes.

b) Differences between Equator and Prime meridian :

(B) 82° 30′ Eastern longitude