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The Rock Cycle

This GCSE Geography quiz will test you on the rock cycle. The countryside around us, including the built environment, is often influenced by what lies underneath our feet - the rocks. Rocks form the Earth's crust and belong to one of three main groups - sedimentary, igneous and metamorphic. Their formation is linked by the rock cycle.

You can jump into the rock cycle at any point and follow it round, ending up back at your starting point. A logical place to start is the summit of a mountain, we can then follow a rock through one of the paths that it can take to end up back where it started. As a rock travels through the rock cycle, it changes from one type to another.

So let's imagine our rock at the top of a mountain.

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For the moment, it doesn't matter what our rock is. It will be subject to weathering by the climate, freeze-thaw is an important one at the top of a mountain. As water gets into tiny cracks in our rock, at night it freezes. As it freezes, the water expands as it forms ice and pushes on the sides of the crack. After many hundreds or even thousands of these freeze-thaw cycles, the crack is enlarged to the point where a lump of the rock falls off. This lump rolls down the hill to form a scree slope or talus.

A combination of gravity and precipitation causes the lump of rock to slowly move down the slope further, eventually ending up in a mountain stream. As it is carried along by the stream, it is broken down into smaller and smaller pieces as the stream becomes a river. Where the river meets the sea (or a lake), the flow of the water slows down and the sediments are deposited on the sea (or lake) floor in layers. As more sediment is added at the top, the weight squeezes out the water from between the grains of the lowest layers of sediment as they are compressed. Chemicals precipitate (un-dissolve) around the grains, cementing them together to form sedimentary rock.

Imagine now that this sedimentary rock is being formed at a destructive plate boundary. Some of it will be pushed back upwards and folded, as a mountain range is formed. Weathering will begin and the sedimentary rock will be recycled.

Some of the sedimentary rock will be taken down with the plate that is being destroyed. Heat and pressure will change it into metamorphic rock, some of which will be uplifted and folded with the sedimentary rocks, also forming part of the mountain range. Weathering then begins and so the metamorphic rock is recycled as sedimentary rock. Some of the sedimentary rock can be taken deep into the mantle where it melts and is recycled as igneous rock.

Finally, all three types of rock can be taken down with the descending plate, to be recycled as either metamorphic rock or igneous rocks. So the next time you hold a piece of rock, just think about what a complex history it may have had!

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  1. Which of the following is the correct sequence that describes the formation of a sedimentary rock?
    Sedimentation and deposition mean the same thing. Sediments are formed in layers which is why the majority of sedimentary rocks are layered
  2. Which rock type is formed by high pressures and temperatures?
    They are formed in the roots of mountain ranges where temperatures and pressures are greatest
  3. At which type of plate boundaries are you most likely to find igneous rocks forming?
    These are the two places that molten magma reaches the surface of the Earth
  4. Which word describes an ingneous rock that is formed deep within the crust of the Earth?
    Granite is a good example of an intrusive igneous rock
  5. Which of the following statements is NOT true?
    It is important to realise that metamorphic rocks are NOT melted during their formation - if they were melted at any point, that would make them an igneous rock
  6. Which of the following statements is incorrect?
    Any crystals that you find in sedimentary rocks are held in place by surrounding particles of sediment and were formed at an earlier date than the rock. The crystals of igneous and metamorphic rocks are formed at the same time as the rocks and are surrounded by other crystals
  7. Which type of rock is made from molten magma that has cooled down and solidified?
    They can form at the surface of the Earth or deep in the Earth's crust
  8. The timescale of the rock cycle is:
    Rocks are millions of years old, some can be hundreds of millions of years old - very few rocks escape being changed by the rock cycle. The oldest rocks on Earth have been dated as being about 4 billion years old and were found in Canada. This means that they have been part of the rock cycle for almost as long as the Earth has existed!
  9. Which of the following is NOT a type of weathering?
    Saltation is a method of transport of rock particles and is therefore erosion and not weathering
  10. In a sequence of sedimentary rock layers, where would you find the most recently formed rock?
    Folding of rocks caused by tectonic movements can cause rock sequences to be turned upside-down! This can sometimes cause problems to geographers when they try to interpret the history of a mountain range

Author: Kev Woodward

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