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* Earth as a Planetary Body

Like all planets in our solar system, Earth rotates on its own axis and goes around the Sun in a definite orbit. The orbit is the path of the Earth around the Sun. This orbit is on a uniform plane which is called the plane of the orbit.

* Actually, the Earth’s orbit is nearly circular , and the difference between the Earth’s farthest point (about 152 million km) from the Sun and its closest point (147 million
km) is very small

* Earth travels around the sun at a speed of 1,07,200 kilometres per hour! At this speed, it takes 365¼ days to complete one revolution.

*The Word Earth

Greek word ‘eorthe’ meaning ground, soil, dry land.’ (Dictionary
Indian languages have multiple words for ‘earth.’ Sanskrit terms include bhoomi, pruthvi, dharani, avani etc.

* The earth is made up of three main layers

1. Crust 2. Mantle 3. Core

1. Crust: The outer part of the earth which is called the crust. This layer goes up to a depth of 100kms. The crust mostly consists of various kinds of rocks.

2. Mantle: It exists at the depths from 100 kms to 2,900 kms. The upper part of the mantle is a pliable layer over which the crust floats. This consists mainly of chemicals called silicates

3- Core: It exists at the depths from 2,900 kms to 6,376 kms. It is composed of dense and heavy substances like iron and nickel. It can be divided into two sub layers.

Outer Core: 2,900 to 5,100 kms composed of liquid metallic material like nickel and iron.

Inner Core: The solid inner core (5,100 – 6,376 kms) of the earth is made up of Iron compounds and heavy substances like gold

* The crust forms only 1% of the volume of the earth, 16% consists of the mantle and 83% makes the core

* In the early 20th century, a German meteorologist and geophysicist Alfred Wagener introduced the theory of continental drift to describe and partially explain the present arrangement of
continents and ocean basins.

* To avoid confusion of time from one place to the other, 82 degree 30’ Eastern longitude is taken as standard Meridian of India and serves as the Indian Standard Time (IST). The exact difference between Greenwich and IST is 5½ hours.

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