教材试题 Unit 5 Listening and Speaking

Unit 5 Meeting your ancestorsListening and speakingThe work on early people depends on the dates that are given to the bones found. If the dates are wrong, all the data about early people may also be wrong. So Zhou Heping is very interested to find out how archaeologists make sure that their dates are accurate.1 Listen to the tape and fill the layers in the “wastepaper basket” diagram on the right. 2 Listen to the tape again. Pay attention to the methods archaeologists use to date bones and how those methods work, then fill in the chart below. MethodHow it works1 Layers in the groundEach layer looks different as they are uncovered, so you can tell where one layer starts and another finishes. In the wastepaper basket, the most recent layer is_, an older layer is below that and the _ layer is _. 2 Radiocarbon datingAll living things have _ in their bodies. When they die, the carbon _ at a _ rate. The method measures_ of carbon in bones or plants using radioactivity and can _ how old the remains are. 3 Look at this archaeological drawing of a section showing buildings at different times and work out their chronological order. Write your answer below, then check with a partner. Remember to give reasons for your answer in your discussion. 1 _2 _3 _LISTENING TEXTDATING METHODSZhou Heping has come to ask the archaeologist, Richard Leakey, how he dates the bones he finds. ZH: How can you tell how old the bones are when you find them?RL: There are two main ways: the first uses layers in the ground and the second uses the radiocarbon dating. ZH: How does the layer method work?RL: Well, many layers of soil were produced at different times. Each time people build houses and live somewhere, they make an occupation layer. Each has a different colour and texture. ZH: How does that help?RL: Look at the diagram in your book. Think of your wastepaper basket. When you came into work you threw the orange skin into it. Later someone threw their empty yogurt pots into it. Then some waste paper was added. Finally someone threw away some used envelopes. How many layers are there?ZH: There are four layers. RL: Good. Now which layer is the latest?ZH: Now, let me think! Yes, itll be the one on the top, which is the used envelopes. RL: And wheres the oldest layer?ZH: At the bottom. RL: Well done. When we find bones in layers of soil, we know they are the same age as the soil. ZH: I see. RL: Now lets think about the second method. ZH: I remember. Its called the radiocarbon dating method. Thats a strange name. RL: Yes. It uses the radioactivity to measure the amount of carbon in living things. The carbon in a dead body disappears at a fixed rate. We know how long this takes, so we can measure the amount of carbon and work out how old a bone or plant is. ZH: Thats very clever. Is it very accurate too?RL: There are some problems, so you are always given a date plus or minus some years. For example, your bone may be dated to 10,000 years ago plus or minus l00 years. This means the bone is between 9, 900 years and l0,100 years old. ZH: How clever! How old are the bones from the Zhoukoudian Caves?RL: They are between 250,000 and 40,000 years old. ZH: Perhaps we can go and visit the site together sometime?RL: Of course. Whenever you like!Answer key for Exercise 1: used envelopeswastepaperyogurt potsorange skinAnswer key for Exercise 2: MethodHow it works1 Layers in the groundEach layer looks different as they are uncovered, so you can tell where one layer starts and another finishes. In the wastepaper basket, the most recent layer is at the top, an older layer is below that and the oldest laver is at the bottom. 2 Radiocarbon datingAll living things have carbon in their bodies. When they die, the carbon starts to disappear at a fixed rate. The method measures the amount of carbon in bones or plants using radioactivity and can work out how old the remains are. Answer key for Exercise 3: This exercise may look difficult but is really very simple. The age of the building depends on the number of layers it is resting on. The more layers, the more recent the building. The oldest building is B because it has no layers underneath it. The second o