CHAPTER FOUR
EARTH’S STRUCTURE AND MOTION
4.1 Earth’s Formation
Earth was formed from a huge cloud of GAS and DUST spinning very
quickly.
The spinning caused the HEAVIER materials to move to the center and
FUSED them into a more solid form.
This spinning motion formed spheres such as EARTH.
Earth is composed of 4 layers:
CRUST
MANTLE
OUTER CORE
INNER CORE
4.2 Earth’s Rotation
Rotation: The turning of a body, such as Earth, on its axis.
Three Major Effects of Earth’s Rotation:
1. Coriolis effect: The effect of Earth’s rotation that causes the deflection
of objects toward the right in the NORTHERN HEMISPHERE and
towards the left in the SOUTHERN HEMISPHERE.
2. DAY and NIGHT (The Earth rotates once every 24 hours).
3. SUNRISE and SUNSET. The sun RISES in the east and SETS in
the west.
The axis of rotation is the IMAGINARY line around which the Earth
rotates. The rate of ROTATION is the speed at which the Earth rotates.
The Earth’s shape is SPHERICAL which causes it to turn further in an
hour at the EQUATOR than at the POLES.
4.3 Earth’s Revolution
Revolution: The movement of one body around the other such as the Earth
in orbit around the sun.
Vernal Equinox: EQUAL SUNLIGHT AND DARKNESS IN
BOTH NORTHERN AND SOUTHERN HEMISPHERES
Summer Solstice: NORTHERN HEMISPHERE: LONGEST
PERIOD OF DAYLIGHT.
Autumnal Equinox: EQUAL SUNLIGHT AND DARKNESS IN
BOTH NORTHERN AND SOUTHERN HEMISPHERES
Winter Solstice: SHORTEST PERIOD OF DAYLIGHT IN THE
NORTHERN HEMISPHERE.
The North Pole has continuous light during the SUMMER SOLSTICE,
while the SOUTH POLE has continuous darkness. During the
WINTER SOLSTICE this is the opposite.
Earth revolves COUNTER CLOCKWISE around the sun and travels
in an ELIPTICAL orbit. It takes ONE YEAR to make a complete
revolution.