2.1 Earth and its features

Natural science

Grade 9

The earth, galaxies and space programmes

Module 13

The earth and its features

THE EARTH HAS FOUR LAYERS:

• Inner core - very dense, unbelievably hot
• Outer core - in a molten state
• Mantle - molten rock
• Crust - solid rock (very thin)

Activity: diagram

Draw a circle and draw in these layers . Use different colours to indicate the different layers.

Assessment of diagram:

Did you indicate the layers correctly?

[LO 2.3]

• The core comprises iron and nickel, and the crust consists of oxygen and silicon.
• In the soft mantle there are silicates, oxides and sulphates.

why does the earth rotate?

• The earth rotates because it falls in the direction of the sun. The sun’s force of gravity causes the earth to revolve around sun and rotate on its axis.
• It is like a ball rolling down a hill.
• The earth revolves once around its own axis every 24 hours.
• Each planet in the solar system also revolves around the sun in its own orbit.
• The earth takes 365¼ days to complete one orbit. This is also called a revolution or, in general terms, a year (‘ earth-year ’).
• It takes each planet a specific number of earth-years to complete one revolution around the sun.
• Mars, has a revolution time of 1,9 earth-years.
• Jupiter takes 11,9 earth-years and Pluto 247,7 earth-years to orbit the sun.

how big is the earth?

split up into groups for the next activity.

Activity: discussion

information on the earth:

Circumference around poles: 40 008 km

Diameter at poles: 12 714 km

Circumference at Equator: 40 075 km

Diameter at Equator: 12 714 km

1. What can you deduce from these statistics regarding the shape of the earth? What could be the explanation for this?

2. Who was Eratosthenes and what did he say 2 000 years ago about the shape of the earth? Discuss this in groups and write down the answers. ( www.union.edu/PUBLIC/GEODEPT/hallocher/sciencelab/Labs/ ND2/LN2.htm)

Assessment of DISCUSSION:

[LO 1.2; LO 1.3]

why is life possible on earth?

• It is the only planet in our solar system where there is an atmosphere with oxygen and where there is surface water. Life as we know it requires oxygen and water!
• The oceans take up about 70% of the earth’s surface.

• The earth’s atmosphere comprises the following gases:

• oxygen (21%)
• nitrogen (78%)
• argon (0.9%)
• carbon dioxide (0.03%)

Activity: circle diagram

Draw a circle. Use different colours, indicating the composition of the atmosphere in percentages in the circle.

Work out the sectors mathematically.

Assessment of circle diagram:

Is your diagram correct? [LO 2.4]

Assessment

LO 1: Scientific investigations:

The learner will be able to act confidently on curiosity about natural phenomena, and to investigate relationships and solve problems in scientific, technological and environmental contexts.

This is evident when the learner:

1.2 conducts investigations and collects data;

• evaluates data and communicates findings.

LO 2: Constructing Science Knowledge:

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

This is evident when the learner:

• interprets information;

2.4 applies knowledge.

Memorandum

The earth and its features

ACTIVITY: HOW BIG IS THE EARTH?

1. The shape of the earth is not altogether round. It is slightly flattened at the poles because its rotation is faster at the equator

2. A Greek philosopher who was the person to show that the earth is round by means of a calculation.

ACTIVITY: PIE GRAPH

The atmosphere consists of 21% oxygen, 78% nitrogen and 0.03 % carbon dioxide, and 0.9 % argon

In diagram: atmospheric gases