Composition and Structure of Earth

Composition and structure of Earth
 Earth is a terrestrial planet, meaning that it is rocky body, rather than a gas giant like Jupiter. It is the largest of the four solar terrestrial planets, both in terms of it size and mass. Of these four planets planets, Earth has the highest density, the highest surface gravity and the strongest magnetic field.
An areal view of our earth

Shape and Size:

For thousands of years people had believed that the earth was shaped like a flat plate that was surrounded by water from all sides. Around 300 BC the famous Greek Philosopher Aristotle presented many arguments to prove that the surface of the earth is curved proving its spherical shape. But in middle ages the Europeans forgot the research and theories of Greeks. They did not remember the arguments of Aristotle that proved the spherical shape of the Earth. In the same period Arabs translated the Greek books and revived their knowledge and proved again that Earth is spherical. In 1519 AD a Portuguese sailor named Ferdinand Magellan set off towards west and went on navigating in the same direction. After the traveling of several years they reached back to Europe via Asia. It was the first travel around the world it proved once again that the Earth is spherical like a ball.
For different purposes the earth is considered round but in fact it is not a perfect circle or sphere. It is flattened at the poles; it is neither a spheriod or ellipsoid. Its shape is an example in its own, as it cannot be shown through any geometrical shapes. Therefore it is named as Geoid or Earth Like.
The average diameter of reference spheroid is about 12,742 km. 
The rotation of the Earth creates the equatorial bulge so that the equatorial diameter is 43 km larger than the pole to pole diameter. The largest local deviations in the rocky surface of the Earth are Mount Everest  (8,848 m above local sea level) and the the Marian Trench  (10,911 m below local sea level).

Chemical Composition of Earth:

The mass of the Earth is approximately 5.98 ×103. It is composed of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulphur (2.9%), nickel (1.8 %), Calcium (1.15 %)  and aluminium (1.4%); with the remaining 1.2% consisting of trace amount of other elements. Due to mass segregation, the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), Sulphur (4.5%), and less than 1 % trace elements.

Distribution of land and water on the surface of the Earth:

The total surface area of the Earth is almost 200,000,000 Sq. Miles; all the oceans cover and area of 141,124,985 Sq.Miles. Thus more than 2/3rd of the earth’s surface is covered with water. At different places of the seas, the depths vary from place to place. The average depth is around 3.52 Km (2.2 Miles).

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