Death of the dinosaurs

Transcription

1 Death of the dinosaurs Q This unit is about how scientists do not always agree. Scientific arguments or controversies can last many years. This is because scientists sometimes explain the facts in different ways. Some scientists may support one theory, and some another. A good example is the debate over the extinction of the dinosaurs. Before you start... For 200 million years dinosaurs ruled the Earth then they became extinct. What do you think killed them? An asteroid? A environmental A disease? disaster? questions Could the same thing happen to us? Yes No Not sure Now do the activities. After you have finished... Once you ve finished the activities, answer the questions below. After studying this unit, do you think scientists know what killed the dinosaurs? Give reasons for your answer. Do you think the dinosaur extinction controversy will be settled one day? What would need to happen to bring this about? Some people think that science is just a lot of facts and theories that everybody agrees on. How is this idea wrong? Use the example of dinosaur extinction in your answer. Here are two scientists explanations about why giraffes have long necks. Darwin: Because those who were born accidentally with long necks were more likely to survive and reproduce. Lamarck: Giraffes have long necks because they are constantly stretching to get to their food. Over the lifetime of a giraffe this gradually changes their shape. How could you find evidence to see which theory is better?

2 What killed the dinosaurs? A 1 Read the storyboard of the TV programme and then answer the questions below. Visuals Script It is 65 million years ago. The T. rex lies writhing on the ground. Drops of blood from its last prey still drip from its huge teeth. All over the world the dinosaurs are dying out. It wasn t only the dinosaurs that died out. Half of all the species on Earth became extinct. These mass extinctions seem to happen about every 26 million years. The next one is overdue. Will we be the victims of the next one? Perhaps if we could find out what caused the dinosaur extinction, we could prepare ourselves. activities In this programme we will examine three leading theories. Some scientists support each one but they disagree with each other. It is a major scientific controversy. Theory 1 says the dinosaurs were killed by a huge asteroid, which collided with the Earth. Theory 2 says that a series of enormous volcanic eruptions wiped out the dinosaurs. Theory 3 says a blast of deadly radiation from space destroyed the dinosaurs. What really killed the dinosaurs? We will try to discover which theory is best.

3 What killed the dinosaurs? A 1 What are the three explanations given for the extinction of the dinosaurs? activities Why was the event 65 million years ago called a mass extinction? What do you think a scientific controversy means? How could we find out which theory is best?

4 Dinosaur debate A 2 In the TV programme, the studio audience is going to decide what they think killed the dinosaurs. They will ask the experts on each theory a series of questions to help them decide which theory is correct. You will take part in the debate. You will play either the part of one of the experts, a member of the audience, or the TV presenter. alternative activities 1 You will be provided with information to help you, on a briefing sheet. Run the studio debate like this: The presenter introduces the speakers and asks for the first question. Members of the audience take turns to ask the experts any questions they choose. The experts answer. At the end of all the questions members of the audience vote individually for which theory they think is best.

5 Extinction theories A 2 Look at the asteroid theory briefing sheet a List three pieces of evidence that support the theory. b What do you think is the best evidence for the theory? Explain. Repeat these questions for the volcano theory and the radiation theory. Draw a table like the one below and put each of these pieces of evidence in the correct box: soot layer, iridium layer, other mass extinctions, tektites, fossil evidence. Evidence which Evidence which the Evidence which the Evidence which all theories can asteroid theory volcano theory the radiation explain cannot explain cannot explain theory cannot explain A popular science magazine publishes this letter: Dino Death Rock I have heard a suggestion that the dinosaurs were wiped out by a volcano. This is rubbish. Almost all scientists agree that the cause was a huge asteroid impact. It is a great scientific detective story. Scientists Walter and Luis Alvarez were studying a layer of clay in Italy, 65 million years old. They found that the dinosaur bones suddenly stopped there. There were none in the layers above. They must have died out suddenly. The scientists then found a huge impact crater on the Yucatan peninsula in Mexico. It was dated at exactly 65 million years ago. What more proof could there be that an asteroid killed the dinosaurs? Mrs A. Ward A. Ward Imagine you are a scientist who thinks the asteroid theory is wrong. How would you reply? Write a letter to the editor of the magazine. Point out any problems with the asteroid theory. Try to persuade readers with the evidence for the other two theories. alternative activities 2

6 Audience member B Your job is to find out as much about the theories as you can, so you can make up your mind which is best. You can ask each expert up to two questions. What the theories are Asteroid theory Volcano theory Radiation theory Don t be afraid to ask the scientists awkward questions. Remember you are looking for the theory that has the best evidence for it. What you know already You have heard that scientists found various substances in the ground that are 65 million years old. You don t know what these substances are. You are puzzled how one disaster could have scattered them all around the world. You have heard that, from fossil records, it seems that many dinosaurs had become extinct before whatever happened 65 million years ago. You have heard that there are other periods in the Earth s history, when most species were wiped out by something. briefing sheet To prepare for the studio debate Think what questions you could ask to find out more about each theory and help you decide which is best. Write them down Questions you might be asked Who you will ask

7 Scientist favouring asteroid theory You believe that an asteroid wiped out the dinosaurs. You are trying to persuade the audience that yours is the best theory for what killed the dinosaurs. How did it happen? A 10 km wide asteroid hurtled towards the Earth at enormous speed and pierced the atmosphere. The heat created a huge fireball, lighting up the sky. Then the impact occurred. The blast and shock wave killed everything in its path. Trillions of tonnes of debris were hurled into the atmosphere. In a short time, dust encircled the Earth, plunging it into thick, black darkness. With no light, vegetation withered. This was followed by famine. The dinosaurs and over half of all species on Earth become extinct. B briefing sheet What s the evidence for your theory? A huge crater, 65 million years old, was found off the coast of Mexico. You believe that the asteroid travelling at high speed produced this crater. A layer of the metal iridium has been found in rocks that are 65 million years old. It is all around the world. Iridium is very rare on Earth but it is found in asteroids. Tektites are small glass beads and have been found around the world in layers 65 million years old. Tektites are made when intense heat vaporises rock. The asteroid that struck the Earth burned up. The impact was so powerful it could have spread small fragments around the world. Are there any problems for your theory? Fossil evidence shows that most dinosaurs became extinct gradually, before whatever event took place 65 million years ago. To prepare for the studio debate: Highlight evidence that best supports your theory. Think what questions you might be asked. Prepare how you will answer them. Write them down in a table like the one below Questions you might be asked Notes for your answers

8 Scientist supporting the volcano theory B You believe that a series of volcanic eruptions wiped out the dinosaurs. You are trying to persuade the audience that yours is the best theory for what killed the dinosaurs. How did it happen? A series of gigantic volcanic eruptions wiped out the dinosaurs. The lava flows were so big, they filled an area the size of France. Each eruption belched out huge amounts of sulphur dioxide gas. This cooled the atmosphere by many degrees. Over the next hundred or thousand years, the Earth was gripped by a terrible global winter. The dinosaurs could not survive such harsh conditions. They became extinct, along with many other animals. What s the evidence for your theory? briefing sheet The Deccan Traps in India is the site of a huge ancient lava flow. It is the size of France. It is exactly 65 million years old. This enormous lava flow would have produced enough gases to cool the atmosphere and cause animals and plants to die. Other mass extinctions have been found in the fossil record. The biggest was 250 million years ago and in it a staggering 95% of life disappeared. In Siberia, scientists have found vast lava flows of exactly that age. Maybe a volcano caused this extinction too. Are there any problems for your theory? Tektites are small glass beads and have been found around the world in layers 65 million years old. Tektites are formed in volcanic eruptions but the beads are so large they do not travel very far A layer of soot is found in rocks that are 65 million years old. This suggests that huge fires were raging at this time. Lava can start fires, but not across continents separated by water. To prepare for the studio debate Highlight evidence that best supports your theory. Think what questions you might be asked. Prepare how you will answer them. Write them down in a table like the one below Questions you might be asked Notes for your answers

9 Scientist supporting the radiation theory B You believe that radiation from space killed the dinosaurs. You are trying to persuade the audience that yours is the best theory. How did it happen? A nearby star exploded as a supernova. It produced a deadly wave of cosmic radiation tiny particles travelling at enormous speeds through space. The radiation destroyed the protective layers of the Earth s atmosphere. A lot of the vegetation and animals were fried. Most of the survivors were then wiped out by radiation sickness or cancer. What s the evidence for your theory? Dinosaur fossils from around 65 million years ago have radioactivity levels seven times greater than older or more recent fossils from the same place. briefing sheet A few dinosaur fossils have been so incredibly well preserved that they are hard to explain for instance, fossilised dinosaur embryos without any sign of decay by microbes. This can be explained if they had been blasted by radiation. Radiation kills the bacteria that would break them down. Are there any problems for your theory? The big problem is that there is no evidence for what caused the radiation from space. Scientists have lots of ideas, like colliding stars, but there is no evidence for any of them yet. To prepare for the studio debate Highlight evidence that best supports your theory. Think what questions you might be asked. Prepare how you will answer them. Write them down in a table like the one below. Questions you might be asked Notes for your answers

10 Controversies E A government report on the danger of asteroids says: An impact like the one 65 million years ago would make the human race extinct. a What evidence is the report likely to be referring to? b Having studied this unit, do you think this statement is correct? Explain your answer. Scientific controversies arise for two reasons: i ii a b Scientists get different data. Scientists have different interpretations for the same data. What are the reasons for the controversy over dinosaur extinction? Explain. Is it possible that all three theories of dinosaur extinction could be correct? Explain your answer. extension c Can you think of any other possible explanations for what killed the dinosaurs? 65 million years ago, when the dinosaurs died out, small mammals survived. So did some reptiles like crocodiles. a Can you suggest reasons for this? b Does this evidence point to a particular theory being correct or wrong? Give a reason. A scientist said this recently: The evidence is that we are in the middle of another mass extinction of animal species. This time it s caused by us. a What evidence might there be for such a mass extinction? b c List several ways that human activity could be causing it. Imagine you disagree with this opinion. Write down arguments against it.

11 Death of the dinosaurs T What really killed the dinosaurs? In this unit pupils debate three theories to learn that there are often several ways to explain evidence. teachers notes Learning objectives Activities (these may be customised using Notes the CD) Ideas and evidence To explain findings, scientists use their imagination. There can be more than one explanation of the same findings, which leads to a scientific controversy [I&E (b)] See CD for references to GCSE syllabuses. Key skills/thinking skills Communication: contribute to a discussion, summarise information. Information -processing: classify, and compare and contrast information. Reasoning: give reasons for opinions. The first page presents an opinion question to get pupils involved and review questions for looking at after the activities in class, for homework, or for discussion. What killed the dinosaurs? This activity introduces pupils to the three theories: asteroid impact, volcanic activity and radiation. Dinosaur debate (alternative 1) A TV debate in the style of blind date about the three different theories for extinction. The studio audience makes up its mind which theory is correct, by asking questions of the pupils who are proposing each theory. Pupils adopt the role of a scientist supporting one of the theories or are in the audience. You could ask each group to write down their conclusions at the end and present them. Note that the real purpose is for pupils to realise that this is a controversy: scientists do not know which theory is correct. Briefing sheets are provided for each role. Scientist briefings show how the theory explains the evidence. The audience brief helps pupils prepare questions. This activity works in groups of about six (one scientist per theory, three members of the audience). Pupils often need help to get into role. One way is to form expert groups beforehand to talk through the evidence for a few minutes. For more information on discussion and role plays, see the general teachers notes on the CD. Where the unit fits in Theory of evolution. Routes through unit All activities except Controversies are intended to be accessible to C/D ability pupils. Timing guidelines The two main activities together require approximately 60 minutes of classroom time. Prior learning None needed. More about dinosaur extinction Visit the PRI website at Language different ways to interpret evidence, scientific controversies. The CD contains a glossary of the terms used in this unit. Extinction theories (alternative 2) A series of structured activities around the three theories. Controversies (extension activity) This is a series of more challenging questions about scientific controversies. Suggestion for further activity Some people suggest we are in the middle of another mass extinction humans are making other species extinct by changing their environments. Research information about this to write a news report. The Pupil Researcher Initiative (PRI) is sponsored by the Engineering and Physical Sciences Research Council (EPSRC), and the Particle Physics and Astronomy Research Council (PPARC).