新课标M8 Unit5 Using Language.ppt

Unit 5 Meeting your ancestors The work on early people depends on the dates given to the bones that are 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. It uses radioactivity to measure the amount of _______ in living things. The _______ in a dead body __________ at a ______ rate. We know how long that takes, so we can measure the amount of _______ and _________ how old a bone is. ZH: How can you tell how old bones are when you find them? ZH: There are four RL: Good. Now which layer is the first and therefore the oldest? ZH: The orange skin. RL: And which is the last and therefore the most recent? ZH: Of course -the used envelopes. I see how it works now. But how does it help? RL: Well, layers of soil are produced at different times like the layers in your wastepaper basket. Each time people live somewhere, they make a layer in the soil. If they live there for a long time, they make a lot of layers. Each layer has a different colour and texture which we use to find out how old it is. ZH: How splendid! ZH: Now what about radiocarbon dating? RL: This is more scientific. It uses the radioactivity to measure the amount of carbon in living things. The carbon in a deadbody disappears at a fixed rate. We know how long that takes, so we can measure the amount RL: Well, the date for a bone may be between 9,900 years and 10,100 years old. ZH: I see! How old are the bones from the Zhoukoudian Caves? RL: They are between 250,000 and 400,000 years old. ZH: Perhaps we could visit the site together sometime? RL: Of course. Whenever you like! THE FEAST: 18,000 BC 北 京 人 北京猿人的化石首次发现于1927年 1929年12月2日发现第一个完整的头盖骨 到1937年已发现的北京人的头盖骨共5个。 1941年12月太平洋战争爆发后,在几个美 国人手里弄得下落不明。 1966年又发现一个残破的头盖骨。 总共发现了属于40多个个体的北京人化 石。时间距今约七十万年至二十万年。 北京人使用过的石器 5. From t