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

1. If one moves towards the east in a straight line he will end up where he started.
2. Satellite photographs taken from space show that the earth is like a sphere.
3. Places in the east see the sun earlier than those in the west.
4. When a ship is approaching the smoke is seen first, then the mast and finally the whole ship.
5. All the planets are spherical so the earth being one of them is also spherical.
6. During the moon eclipse the earth casts a spherical shadow on the moon.
7. 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:

1. Rotation of the earth on its axis
2. 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

1. 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).
2. Causes deflection of winds and ocean currents in the N hemisphere to the left and in the S hemisphere to the right.
3. It causes rising and falling of ocean tides.
4. Causes time difference between longitudes.

• Takes one hour to go through 15◦.

• 4 min to go through 1◦.