Natural Sciences and Technology Grade 5-B ... - Thunderbolt Kids

3 Sedimentary rocks
VISIT
Dierent rock types
(video)
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KEY QUESTIONS
• Why does the Earth have mountains and valleys?
• Have mountains always looked like they look now?
• Why can you sometimes see "layers" in rock which
are dierent colours? How did these layers form?
Teacher's Note
Chapter 3 deals with one kind of rock - sedimentary rock. This
does leave one wondering what other types of rock there are. The
main other type of rock is igneous rock. That is rock that has been
hot and molten, and pushed up from deep in the mantle. Mostly it
hardens under the ground and we see it only millions of years later
when erosion has removed the ground over it. Sometimes it breaks
through the crust as molten lava, and we have a volcano. The top
of the Drakensberg is the remains of ahuge outpouring oflava
long ago. Nature is always breaking down rock and eroding it, so
mountains are always changing. They change so slowly that we
cannot notice it in aperson's lifetime, but the changes are
happening all the time.
We saw in Chapter 2 that the surface of the Earth is made up of
rocks and soil. There are dierent soil types, but did you know that
there are also dierent types of rock? We classify rocks depending
on how they were formed.
We are only going to look at Sedimentary rock in this chapter and
find out how it is formed and used.
3.1 Formation of sedimentary rock
In Chapter 2, we saw how rocks break up into smaller and smaller
pieces, until we have grains of sand. Now we find out what
happens to the sand.