THE ORIGIN OF THE EARTH
- A star with a greater gravitational pull passed near the sun
- It attracted large quantities of gaseous materials from the sun
- The materials split, cooled and condensed
- Heavier materials collected at the centre to form the core
- Less dense materials collected around the core to form the mantle
- The lightest materials formed the crust
The shape of the earth
The shape of the earth is called geoid/ovoid/oblate spheroid due to being an imperfect sphere by being wide at the equator and flat at the poles.
Proofs/Evidence That the Earth Is Spherical
- If one moves towards the east in a straight line he will end up where he started.
- Satellite photographs taken from space show that the earth is like a sphere.
- Places in the east see the sun earlier than those in the west.
- When a ship is approaching the smoke is seen first, then the mast and finally the whole ship.
- All the planets are spherical so the earth being one of them is also spherical.
- During the moon eclipse the earth casts a spherical shadow on the moon.
- The earth’s horizon appears curved when observed from a very high point like a tower.
The size of the earth
- Equatorial diameter-12756km
- Equatorial circumference-40085km
- Polar diameter-39995km
- Surface area of the earth-510×106 km2
- Water surface-73%.
The Movement of the Earth
There are 2 movements of the earth namely:
- Rotation of the earth on its axis
- Revolution of the earth around the sun
Rotation of the Earth
-Movement of the earth on its own axis (imaginary line through the centre from N pole to S pole.
- Rotates through 360◦.
- Takes 24 hours (day) to complete 1 rotation.
- Rotates in an anticlockwise direction (west to east).
Effects of Rotation of the Earth
- Creates day and night because at any one time one side of the earth faces the sun (day) and the other remains in darkness (night).
- Causes deflection of winds and ocean currents in the N hemisphere to the left and in the S hemisphere to the right.
- It causes rising and falling of ocean tides.
- Causes time difference between longitudes.
- Takes one hour to go through 15◦.
• 4 min to go through 1◦.
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