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CHAPTER 2
EARTH
OUR HOME
Learning Outcomes
You Will Learn:
• that the Earth is fragile
Lead-in: Looking at the Earth from Space
(Answers)
World’s first view of Earth (23 August 1966)
Taken by a spacecraft near the moon
(Source: NASA)
1. I would feel in awe of the view of the Earth from outer
space and even find it mysterious.
2. Yes, the Earth could be destroyed if a large asteroid hits our
planet. This is a theory that has often been used to explain
the extinction of dinosaurs.
The Solar System
The Solar System
SUN
VENUS
MARS
SATURN
NEPTUNE
PLUTO
MERCURY
JUPITER
URANUS
EARTH
(Third planet from the Sun)
• The solar system consists of nine planets and the
Sun
• The nine planets orbit round the Sun
• The planet closest to the Sun takes the shortest
time to orbit around the Sun
• The Earth is the third planet from the Sun
Revolution of the Earth
• The Earth, while rotating on its axis, also revolves around the Sun
• One orbit or revolution of the Earth around the Sun takes 365 ¼
days (1 year)
• Due to the revolution and tilting of the Earth, different places on
Earth receive different amount of heat and sunlight from the Sun
• The combined effect of the Earth's revolution and its tilt results
in the seasons in some parts of the world
Earth tilted at 23.5o
Northern
Hemisphere
Axis
Southern
Hemisphere
Equator
June
Summer in Northern Hemisphere
Winter in Southern Hemisphere
December
Winter in Northern Hemisphere
Summer in Southern Hemisphere
Rotation of the Earth
• The Earth spins from west to east on its axis
• This movement is known as a rotation
• The Earth’s axis of rotation points in the same direction
throughout its revolution around the sun
• One rotation takes 24 hours (1 day) to complete
Axis
The part of the Earth
that faces the Sun
experiences day.
North Pole
The part of the Earth
that does not face the
Sun experiences night.
South Pole
Fragile Earth
• To our knowledge, the Earth is the only planet in the Solar System
with an environment that is suitable for living things
• The Earth provides us with the materials and conditions to live
comfortably
• However the Earth is fragile because it can be damaged by
human activities, such as pollution and depletion or Earth’s natural
resources
• Therefore we have to learn to use the Earth’s resources wisely to
protect our environment
Skills Builder: Suggested Answers
For life to be possible on a planet, it must have:
• gravity somewhere between 50% and 150% of the Earth's gravity;
• an atmosphere with the right amount of oxygen, very little carbon
dioxide, lots of liquid water; and
• an average temperature somewhere above freezing point of
water and somewhere below boiling point of water
Additional Resources from Multimedia TEACH Resources
Photo Bank
Image A
Image B
Photo 2-1
As far as we know, the Earth is the only planet in the Solar System that
supports life. Compare the satellite image of the Earth (Image A) with the
satellite image of Mars (Image B). How are they different?
Additional Resources from Multimedia TEACH Resources
Photo Bank
Polar ice cap in 1979
Polar ice cap in 2003
Photo 2-2
Human activities have an impact on the physical environment. The satellite
images, taken in 1979 and 2003, show that the polar ice caps in the North
Pole have reduced in size to a large extent over a 24-year period. Why do
you think so?