Inside Our Earth

The Earth is made of three concentric layers. The uppermost layer, the crust, is the thinnest: about 35 km thick on the continents and only about 5 km on the ocean floors. The continental crust is made mainly of silica and alumina (sial), while the oceanic crust is mainly silica and magnesium (sima). Below the crust lies the mantle, which extends to a depth of about 2900 km. The innermost layer is the core, with a radius of about 3500 km, made mainly of nickel and iron (nife); it has very high temperature and pressure. Rocks are natural masses of mineral matter. Igneous rocks form when molten magma cools: intrusive rocks such as granite cool slowly inside the crust, and extrusive rocks such as basalt cool quickly on the surface. Sedimentary rocks, like sandstone, form from layers of compressed sediments and may contain fossils. Metamorphic rocks form under great heat and pressure, as clay changes into slate and limestone into marble. Rocks keep changing from one type to another in the rock cycle.

Detailed Worksheet: Inside Our Earth Section A - Definitions (10 marks) 1. Name the three layers of the Earth in order from the surface. (2 marks) 2. What are sial and sima? (2 marks) 3. What is a rock? What is a mineral? (2 marks) 4. What are fossils? In which type of rock are they found? (2 marks) 5. What is the rock cycle? (2 marks) Section B - Calculations and Applications (15 marks) 6. The crust is about 35 km thick under continents and 5 km under oceans. (i) How many times thicker is the continental crust? (ii) The mantle extends to 2900 km; find its approximate thickness below a 35 km continental crust. (iii) Which layer is the thinnest? (3 marks) 7. The Earth's radius is about 6400 km and the core's radius about 3500 km. (i) Find the combined thickness of the crust and mantle. (ii) What fraction of the Earth's radius is the core (to one decimal place as a decimal)? (iii) What is the core made of? (3 marks) 8. Classify these rocks as igneous, sedimentary or metamorphic: granite, sandstone, marble, basalt, slate, limestone. (3 marks) 9. State the rock that each changes into under heat and pressure: (i) clay (ii) limestone (iii) sandstone. Give one use of each metamorphic rock. (3 marks) 10. The deepest mine in the world is about 4 km deep. The centre of the Earth is about 6371 km deep. What percentage of the distance to the centre is the mine (to two decimal places)? What does this show? (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of the interior of the Earth showing the crust, mantle and core with their approximate depths. (4 marks) 12. Draw a labelled diagram of the rock cycle showing igneous, sedimentary and metamorphic rocks and the processes linking them. (3 marks) 13. Draw a diagram showing the formation of intrusive and extrusive igneous rocks near a volcano. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. (i) Why can't we travel to the centre of the Earth? (ii) How do scientists know about the Earth's interior? (iii) Why is the core so hot? (iv) Compare the crust to the skin of an apple and the core to the seed: is this a good comparison? Explain. (v) What is the importance of the mantle? (5 marks) 15. The Taj Mahal is built of white marble, and the Red Fort of red sandstone. (i) What type of rock is marble? (ii) What type is sandstone? (iii) How did each form? (iv) Name two other uses of rocks in daily life. (5 marks) 16. A fossil of a sea shell was found on a mountain in the Himalayas. (i) In what type of rock was it found? (ii) What does it tell us about the past of the region? (iii) How are fossils formed? (iv) Why are fossils important for scientists? (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Label diagrams with approximate depths in kilometres.