1. CAPE 2009 U1/P2/#7
a) Name the layers labeled A, B, C and D. [4 marks]
A- Inner core
B- Outer core
C- Lithosphere
D- Asthenosphere
b) “The tectonic cycle consists of the recycling of the upper few kilometres of the
Earth.”
Describe the stages in the recycling referred to in the statement above. [6 marks]
Plate tectonics is the study of the movement of plates and their resultant landforms. The
tectonic cycle consists of the recycling of the upper few kilometres of the Earth. Since the Earth
is neither expanding nor shrinking, new oceanic crust is formed at one place and destroyed at
another.
Destructive margins occur where continental and oceanic plates converge. As the oceanic
crust cannot override the continental crust as it is denser, it is forced to dip downwards at an
angle to form a subduction zone. The heat produced by friction helps to convert the disappearing
crust back into magma.
Constructive margins occur where two plates diverge from each other and new crust is
created at the boundary. As the plates diverge, molten rock or magma rise from the mantle to fill
any possible gaps between them and, in doing so, creates new oceanic crust.
The stages therefore show how the upper few kilometres of the Earth is recycled.
c) Explain how the composition of the lava and the type of eruption account for the
shape of THREE types of volcanoes. [20 marks]
A volcano is a natural vent or fissure