Before 500 BC, people thought that earth was flat. But thanks to scientists like Aristotle and Pythagoras, people know that the shape of the earth is spherical. However Sir Isaac Newton showed that the earth was not a perfect sphere, but a compressed spheroid.
The correct technical term to use will be oblate spheroid, a type of ellipsoid solid formed when an ellipse is rotated about its minor axis.
The study of size and shape of earth is called geodesy.
The diameter of earth at poles is 12715 km (minor axis)
The diameter of earth at equator is 12763 km (major axis)
STRUCTURE OF EARTH The structure of earth (also referred as cross–section) is divided into mainly four layers namely Crust, Mantle, Inner Core and Outer Core .
COMPOSITION OF EARTH As discussed earlier, the mass of the Earth is approximately 5.98×10 24 kg. When taken as a whole, the Earth's chemical composition (by mass) has been approximated as given in the table below. The students should remember the top three with their percentages S.No. Component Percentage by Mass 1 Iron 34.6% 2 Oxygen 29.5% 3 Silicon 15.2% 4 Magnesium 12.7% 5 Sulfur 2.4% 6 Nickel 1.9% 7 Calcium 1.5% 8 Aluminium 1.4% 9 Trace Elements 0.8%