3. Warm up
1) From where does the
sun rise?
2) From where does the
sun set?
3) Have you ever thought
why this happens?
4. OUR PLANET—EARTH
1. The earth is the only planet that has an
atmosphere containing about 21 percent
oxygen.
2. It is the only planet that has liquid water on its
surface and this is why the earth appears blue
from space.
3. It is also the only planet in the solar system that
has life in the form of plants, animals, insects,
birds and human.
6. THE STRUCTURE OF THE EARTH
• The earth was formed millions of years ago from a cloud
of dust and hot gases. Initially, it was very hot.
• With time, the hot gases gradually formed clouds. There
were continuous rains that cooled the outer surface.
• So, the surface became hard on cooling. Water appeared
on the surface in liquid form.
• The gases formed the atmosphere. Slowly, the conditions
became suitable for life to take form.
• The earth is made up of three layers—crust, mantle and
core.
7. • The outermost layer of the earth is called the crust. It
is made up of rocks, mainly granite and
basalt.
• The layer below the crust is called mantle. It is hot and
made up of a thick layer of rocks rich in minerals such as
iron and magnesium.
• The innermost layer of the earth is very hot and it is in
a molten state. It is known as the core and is made up
of dense minerals, mainly iron and nickel.
8.
9. The molten material present in the core is known as
lava or magma. It gushes out with great force from
cone-shaped mountains which are known as volcanoes.
The hole from where the lava comes out is known as
the crater.
15. The earth’s axis is
not perpendicular
to the plane of the
Earth’s orbit.
The axis is tilted
23.5º with respect
to the plane of
movement around
the Sun.
16. The consequences of rotation
The rotation of the
Earth every 24 hours
causes day and night.
• It is day on the side
of Earth where the
sun shines.
• On the other side of
Earth is night.
17. The consequences of rotation
Rotation, seen from North Pole, is anticlockwise
(from west to east) .
18. So the Sun rises in the east.
Sunset: when the Sun disappears at the
end of the day.
Sunrise: when the sun first appears
in the morning
21. The consequences of revolution:
the seasons
Three factors cause the seasons:
• The revolution of the Earth around the Sun
• The tilt of the Earth’s axis of rotation respects to
the Plane of the Ecliptic.
• The tilt of the Earth’s axis remains constant.
22. The tilt of the axis causes:
Differences in temperature
Differences in the duration of day and night.
23. Revolution causes:
- The four characteristic positions of
the Earth (Summer and winter
solstices and spring and autumn
equinoxes).
- The seasons of the year
26. The Seasons
The sun is not at the
exact centre of the Earth’s
orbit and the Earth’s orbit
around the Sun is not a
perfect circle.
So, the distance of the
Earth from the Sun varies
as the Earth revolves
around the Sun.
27. The seasons in the Northern
Hemisphere
During the summer in the northern hemisphere, the Earth is farther
away from the Sun. The temperature is higher because there are more
hours of daylight and because the Sun’s rays hit the Earth’s surface at an
angle of 90º.
28. During the seasons, temperature changes
depend on angle at which the Sun’s rays hit
the Earth.
29.
30. The seasons are caused by:
The movement of the Earth around the
Sun.
The tilt of the Earth’s axis of rotation.
The fact that the tilt remains constant.
