Big Bang Theory

Also know as Expanding Universe Hypothesis, it can be credited to Edwin Hubble who provided evidence of expanding universe n 1920. is theory was postulated in 1950s and 1960 s and validated in 1972. According to this theory everything in the universe emerged from a point known as singularity, about 13.7 billion years ago.

The Big Bang

The galaxies moved apart as the space between them expanded (A galaxy is a large rotating aggregation of stars held together by gravity). Obviously the universe was much smaller in the beginning. As the universe expanded the hot radiation in the original rewall also expanded and cooled down. Misty clouds of matter already existed. As those clouds collapsed upon themselves they were pulled together by their own gravity and formed clusters of galaxies with the galaxies themselves breaking up into stars like those of the Milky way. The stars might have broken up to form their planets like those of our solar system.

Geological History of India

The earth has passed through dierent geological stages ever since it assumed solid surface. The main purpose of studying the geological history of the earth is to establish the succession of geological events and to work out a ‘geological time scale’. “The geological time scale refers to the chronological programming of various geological forms and forms of life in the past according to their time and place of origin, evolution and extinct. In other words it deals with the distribution of rock formations and animals since the beginning of life on the earth.” On the geological scale, the longest time span is called an era which is divided into periods. The period in its turn is divided into epochs. s division is like years, months and days in a calendar.

Shape and Size of the Earth

The Earth is usually considered as a sphere. However, more precise measurements indicate that there is slight flattering of the earth at the poles and slight bulging at the equator. Thus the Earth is not a perfect sphere but an oblate spheroid or an oblate ellipsoid. According to the latest calculations, the earth’s equatorial radius is 6378.245 km and the polar radius is 6356.863. This gives a difference of 21.382 km, between the equatorial and polar radius. e  The oblateness of the earth ellipsoid or flattening of the poles or polar compression is the ratio of this difference to the equatorial radius which works out  to be 1/298.3. By considering the lengths of equatorial and polar radii of the earth, it is seen that the polar radius is approximately 21 km shorter than the equatorial one which looks quite insigniant when compared with the size of the earth.

Difference between sphere and spheroid

Latitudes and Longitudes

These are imaginary lines, rather circles drawn on a globe or a map to know the exact location of a specipoint on the earth’s surface.


The earth is supposed to be rotating around an imaginary line running through its centre. Thus imaginary line is called the axis of the earth. The northern end of this axis is called the North Pole and its southern end is known as the South Pole. Equidistant from these two poles runs the central-most parallel, known as the equator. It divides the earth into two equal parts known as hemispheres. The hemisphere which lies to the north of the equator is called the northern hemisphere while that lying to the south of the equator is known as the southern hemisphere.

Earth’s History

The development of the earth and life on the earth. At the top of the chart is earth’s recent history and at the bottom is given its earliest history. The equator is the initial line indicating 0° latitude. All other latitudes are measured with reference to the equator. The latitude of a place is its angular distance along a meridian on the earth’s surface, as measured from the centre of the earth. If a place is located in the northern hemisphere and makes an angle of 30° along meridian, as measured from the centre of the earth, then the place will have a latitude of 30° north. Line joining places of equal latitude is known as parallel of latitude. Equator is the longest parallel. The length of the parallels goes on decreasing as we move from equator towards the poles till it is reduced to zeros at the two poles.

Meridians and Longitude


Also called lines of longitude, meridians are imaginary lines which join the poles and are perpendicular to all parallels. They are drawn as semi-circles on the globe. The Meridian pas sing through the Royal Observatory at Greenwich near London is designated as the Prime Meridian or Greenwich Meridian and represents 0°. The exactly opposite to the Green wich Meridian is longitude of 180° and is known as the international date line. The other longitudes are drawn between these two important longitudes. The prime meridian divides the earth into eastern and western hemispheres. Places lying in the east of the prime meridian are said to have east longitudes while those in the west of the prime meridian have west longitudes. Prime meridian (0° longitude) and international date line (180° longitude) are common and are not designated as east or west longitudes.


The longitude of a place is its angular distance measured in degrees east or west from the prime meridian. The places located in the east of the prime meridian have east longitude whereas those located in the west of it have west longitude. When we say that the longitude of Allahabad is 82½° east, this means that Allahabad is located in the east of the prime meridian and makes an angle of 82½° with the axis of the earth with reference to the prime meridian Thus longitude is written as long. 82½° E and is read as longitude 82½° east of Greenwich.


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