Answers to Coursebo0k questions Unit 8 The Earth Topic 8.1 Rocks, minerals and soils 1 A geologist is a scientist who studies rocks. 2 A mineral is made of one substance, whereas a rock is made of a mixture of things, such as different types of mineral. 3 Feldspar, mica and quartz are found in granite. They can be seen as crystals in the rock. Accept any named minerals and that they are found in rocks. 4 The properties of soils are important for growing crops because the soil provides water and minerals to the growing plants. If a soil drains too quickly the plants will not get enough water. If the soil becomes waterlogged quickly the plants will die as the air spaces in the soil fill up and they cannot get any oxygen to the roots. Give credit to those students who link the ideas about some crops preferring acidic or alkaline conditions, as in Unit 7, Material changes. Credit any reference to the amount of humus in the soil giving increased amounts of mineral salts.
Topic 8.2 Soil Activity 8.2B Looking at the composition of soils A1 Use the same volumes of soil and water, and identical of glass containers, so that the relative thicknesses of each layer can be compared. A2 The heaviest particles are at the bottom of the container. A3 The lightest part is floating on the surface. This may consist of parts of plants and credit should be given for identifying them. A4 The comparison should refer to the basic descriptions of the two soils – for example, their colours, how wet or dry they are. Specific reference to the thicknesses of each layer should be made.
Activity 8.2C Investigating soil drainage A5 Which soil drains more quickly. A6 Variables kept the same: the volume of soil used, the volume of water used, the apparatus used and the volume of water collected. A7 The time taken to collect a given volume of water. A8 The soil from which the given volume of water is collected in the shorter time will be the one with the better drainage. A9 There should be specific reference to the times taken to collect the water that has drained through. There should be a statement as to which of the soils drained more/less quickly.
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Topic 8.3 Igneous rocks 1 Granite cooled more slowly when it was formed. We can tell that this is the case because granite has large crystals. 2 Obsidian and pumice must have cooled extremely quickly, so there was no time for crystals to form. 3 Magma gets to the surface of the Earth when volcanoes erupt.
Topic 8.4 Sedimentary rocks 1 The clues would be that there are grains in the rock and that the rock is porous. There may be fossils in the rock. 2 Sedimentary rocks are porous because the grains are squashed together with spaces between them. This leaves spaces for water to get in. 3 Fossils are never found in igneous rocks because igneous rocks are formed from molten rock that has come from deep inside the Earth. 4 Pumice is porous because it cooled so quickly that bubbles of gas were still trapped in the rock as it cooled. This left holes in the rock.
Activity 8.4 Porous rocks A1 The rock that increases in mass more after soaking in water is more porous. A2 The variables that should be kept the same are the volume of the rock samples and the length of time for which each rock is in the water. A3 It is difficult to make sure the volume of each rock sample is the same.
Topic 8.5 Metamorphic rocks 1 Limestone and marble are both made of calcium carbonate but have different properties because the particles are arranged differently. In limestone, a sedimentary rock, the grains are squashed together. This gives the rock a grainy appearance and it is porous as there are spaces between the grains. Marble is a metamorphic rock and has been formed by the action of heat and pressure on limestone. This pushes the grains closer together and the spaces between them are reduced, so the rock appears less grainy and is harder. 2 Quartzite is formed by the action of heat and pressure on sandstone. 3 If the original rock was a sedimentary rock, then it’s possible that the metamorphic rock will contain fossils, but they are likely to be very squashed and difficult to make out. Sometimes you can see fossils in polished marble paving stones.
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Topic 8.6 Weathering 1 Weathering is when rocks get slowly broken down by rain, wind, frost and temperature changes. 2 Chemical weathering is when chemicals in the air or rain change rocks. 3 An example of chemical weathering is that caused by rainwater, which is slightly acidic. Limestone is made of calcium carbonate. When acid reacts with it, carbon dioxide gas, water and a salt are produced. The carbon dioxide gas goes into the air and the other products are washed away by the rain. Rain is a very weak acid so the reaction is only very slight. It takes many years to notice the differences caused to the limestone. 4 Water gets into the spaces and cracks in rocks. When this water freezes, it expands. This makes the cracks larger. When the water melts the larger cracks are left. When this happens many times the rocks are broken up. 5 The Sphinx has been in the desert for thousands of years. The details of the statue are not as clear as they were when it was first made. Over this time the wind has blown fine particles of sand and dust against it. This has worn away the surface of the statue. 6 Plants can grow in the cracks in rocks, which causes further cracking. In addition, the plant holds moisture, and the shade from the plant means that different parts of the rock are at different temperatures in the sunshine. This can lead to more cracks and damage to the rocks. Other examples, such as weathering caused by the acids from limpets, can be credited.
Activity 8.6 Acid and rocks A1, A2
The answers will depend on the rock samples provided.
Topic 8.7 Moving rocks 1 Rock fragments are formed by weathering. 2 Rock fragments are moved by gravity, rain, wind and rivers. 3 ‘Deposition’ means that the rock fragments settle on the bottom of the river. They can no longer be carried by the river because they are too heavy – the slow-moving water does not have enough energy to carry them. 4 Heavier fragments can only be carried a short distance, while lighter ones can be carried further. The speed of the river, which is affected by the slope of the ground, changes – the slower it flows, the less energy the moving water has and the lighter the fragments that can be carried. Copyright Cambridge University Press 2012
Unit 8
5 The layer at the bottom is the oldest. Over time, more sediment is deposited on the top. This pushes down on the older layers and over millions of years it forms sedimentary rock. 6 The term ‘abrasion’ refers to the smoothing of rock fragments. When the rock fragments are first formed they have sharp edges. As the fragments move against each other, the sharp edges are worn away and the surfaces become smoother.
Topic 8.8 Fossils 1 Fossils are the remains of the bodies of plants and animals that are found in rocks. They may also be made from the tracks or marks an organism has left in the mud. 2 Fossils are found in sedimentary rocks. 3 Fossils are made when animals and plants die and become part of sedimentary rocks. As the layers build up, the rock becomes solid and the minerals in the rock replace the minerals in parts of the dead bodies. This takes place over millions of years. 4 We know that coal was not formed in seas because the plant fossils found in coal are similar to modern day ferns. We know these must have lived on land. 5 Fossils tell us about life on Earth millions of years ago. They can also sometimes tell us about how and where rocks were formed.
Topic 8.9 The fossil record 1 The oldest species of horse in the fossil record is Hyracotherium. 2 Mesohippus is older than Pliohippus. 3 According to the diagram in the Coursebook, Equus, the modern horse, appeared on the Earth between 5 million and 2 million years ago. 4 Birds have wings that are similar to those of Pterosaurs and reptiles have mouths and teeth that are similar to it, but there no animals alive today that are exactly like Pterosaurs. 5 Fish first appeared on the Earth about 500 million years ago. 6 The insects appeared on the Earth before the flowering plants. 7 The first seaweeds appeared on Earth about 1000 million years ago.
Topic 8.10 The age of the Earth 1 the core 2 iron and nickel 3 Wegner’s evidence for his idea of continental drift was that the shapes of the continents fit together, Cambridge Checkpoint Science
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the rocks on the continents match up where they fit, and the fossils in the rocks match up where the continents fit. 4 Some people rejected his idea because he could not explain how the continents moved. 5 The answer will depend on where the student lives. 6 Earthquakes and volcanoes occur at the plate boundaries.
Topic 8.11 The geological time scale 1 2 3 4
the Cenozoic 251 million years ago the Paleozoic Students might suggest that it may make it easier for geologists and other people to think about them, or that it may be easier to remember names rather than ranges of dates. 5 a The oldest rocks in North America are more than 542 million years old. b The oldest rocks in North America are found in the Rocky Mountains and in Central Canada. 6 The rocks found at the surface close to New Orleans are less than 65 million years old.
End of unit questions 8.1 a Rock D is an igneous rock. [1] b Rock E is a metamorphic rock. [1] c i A fossil is the hard remains of the bodies of plants and animals that have not decayed, or
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Unit 8
traces left by them. The minerals in the bodies, or traces, have been replaced by the minerals in the rock. [2] ii Rocks B and C could contain fossils. [1] d Sedimentary rocks were formed when small fragments of rock and mud were deposited in the sea. Layers built up as more and more was deposited. The pressure of the layers above squashed the grains together and they became solid rock. [4] e Any two from: Sedimentary rocks are porous and igneous rocks are generally non-porous. Sedimentary rocks may contain fossils, while igneous rocks do not. Sedimentary rocks are made up of grains of material, while igneous rocks are generally made up of crystals. Sedimentary rocks are softer than igneous rocks. [2] 8.2 a x-axis labelled, with unit both y-axes labelled, with correct units suitable scales on one or two axes suitable scale on third axis all points correctly plotted clean lines drawn
[1] [1] [1] [1] [1] [1]
b The data show that there is a greater and greater mass of fragments deposited the further along the tubing from the start they travel. [2] c The diameter of the rock fragments deposited decreases the further they go along the tubing from the start. [2]
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