In this presentation you will:

1. Analyze and Evaluate Scientific Explanations In this presentation you will: • explore how scientists analyze and evaluate scientific explanations Next >

2. Introduction Science is about trying to find the answers to questions. Questions such as “Why are there no dinosaurs alive today?” Scientists make observations, gather data and develop explanations of the natural world. Next >

3. Explanation Why are there no dinosaurs alive today? One scientific explanation for this is: “Dinosaurs are extinct. They suddenly became extinct 65 million years ago as the result of a large asteroid hitting the Earth on the coast of Mexico.” How do we know this explanation is valid? Looking at how this explanation was developed will give you a good insight into how Earth science works. Next >

4. Analyzing and Evaluating In science we can analyze and evaluate scientific explanations in a number of ways: • Looking at the empirical evidence (measurements) • Using logical reasoning • Carrying out observations • Experimental testing • Looking at alternative explanations Let’s look at the empirical evidence (a record from observations that can be measured)… Next >

5. Dinosaurs How do we know dinosaurs actually existed? Fossils are the remains of organisms that died and were preserved. Huge numbers of fossils of dinosaurs have been found. Next >

6. Dinosaurs Dinosaur fossils have been found in rocks aged between 230 – 65 million years old. Dinosaur fossils have been found all over the world. Dinosaurs lived on Earth for over 160 million years. Next >

7. Question 1 We know dinosaurs existed because we have found their fossilized remains. Is this statement true or false? Answer True or False. Next >

8. Question 1 We know dinosaurs existed because we have found their fossilized remains. Is this statement true or false? Answer True or False. True Next >

9. Where Did They Go? Dinosaur fossils have not been found in rocks less than 65 million years old. Possible explanations for this include: • they changed into something else • they became extinct • the environment changed so that they were not fossilized Next >

10. Evolution Did the dinosaurs evolve into something else? When scientists look at the fossil record they see an abrupt end to dinosaur fossils. Evolution occurs slowly, and scientists would have seen a slow change in the fossil record. Some forms of dinosaurs did evolve into birds, but this occurred much earlier. Next >

11. Extinction Did the dinosaurs become extinct? Younger rock As well as dinosaurs, scientists have also observed that fossils of many other organisms that existed 65 million years ago are not found in younger rocks. Older rock This observational testing indicates that an event may have taken place that caused the extinction of many species. Next >

12. Fossilization Did the environment change so that dinosaurs were not fossilized? When scientists look at the fossil record they do find fossils of some organisms other than dinosaurs in younger rocks. Logical reasoning tells us that it was not simply the case that dinosaurs were prevented from becoming fossilized. Next >

13. Question 2 No fossils of any creature have been discovered in rocks younger than 65 million years old. Is this statement true or false? Answer True or False. Next >

14. Question 2 No fossils of any creature have been discovered in rocks younger than 65 million years old. Is this statement true or false? Answer True or False. False Next >

15. Extinction The data from fossils leads to the conclusion that dinosaurs became extinct 65 million years ago. There is a distinct boundary between rocks at this period. This boundary is named the K-T boundary. It is found in many parts of the world. Next >

16. The K-T Boundary Below the K-T boundary are found fossils of dinosaurs. Above the K-T boundary there are no dinosaur fossils. The K-T boundary also marks the extinction of many plants and ammonites. Scientists recognized that a mass extinction had occurred at the K-T boundary. Next >

17. The K-T Boundary Scientists investigated the K-T boundary layer and discovered: • it is similar in many locations of the world. • it is dated to around 65 million years ago. • it contains strangely high amounts of a substance called iridium. Next >

18. Iridium Iridium is an extremely rare metal element similar to platinum. However, it is common in asteroids and meteors. The high level of iridium that was found as a result of experimental testing was good evidence that an impact had occurred. Next >

19. Finding the Crater One of the predictions made by the asteroid impact hypothesis is that there should be a crater. It took scientists 10 years, but eventually a 110 mile wide crater was identified on the coast of Mexico. The crater is buried deep beneath the surface but has been dated to the right period. Next >

20. Impact The effect of an asteroid hitting the Earth would have been catastrophic. Would it be enough to cause the extinction of 70% of species on Earth? Scientists used computer modeling to find out. Scientists also carried out experimental testing by firing balls into sand and taking measurements which could then be scaled up to the size of the asteroid. Courtesy NASA Next >

21. Impact Effects The energy of a 10 km asteroid would be the same as 300 million nuclear weapons and create temperatures hotter than the Sun's surface. The expanding fireball of superheated air would wipe out organisms near the impact. Next >

22. Impact Effects Other effects would include intense heat, massive blast waves, fiery rain and massive tsunamis. Next >

23. Impact Effects The vapor and debris thrown into the atmosphere would block sunlight and lower temperatures. Plants would die, then herbivores, followed by the carnivores. A small number of organisms may survive for a short time on any remaining seeds, roots or decaying matter. Next >

24. Question 3 What led scientists to believe an asteroid had hit the Earth to wipe out the dinosaurs, even before they had located the crater? A) The KT is found in many places in the world B) Debris was scattered around the world C) There were strangely high levels of iridium at the KT boundary layer D) They did not suspect an asteroid until they found the crater Next >

25. Question 3 What led scientists to believe an asteroid had hit the Earth to wipe out the dinosaurs, even before they had located the crater? A) The KT is found in many places in the world B) Debris was scattered around the world C) There were strangely high levels of iridium at the KT boundary layer D) They did not suspect an asteroid until they found the crater Next >

26. Alternative Theories - Volcanism Huge eruptions of lava in India were occurring around 65 million years ago. We can reason that these huge eruptions would have changed the climate. They occurred over a period of a few million years. Next >

27. Alternative Theories – Climate Change Climate change did occur at this time which may have led to the gradual extinction of the dinosaurs. However dinosaurs had been around for over 160 million years and been through many changes of climate and successfully adapted. Next >

28. Summing up the Evidence Although there are a number of alternative theories, the evidence towards the theory of the asteroid is substantial. Dinosaur fossil records suddenly stop 65 million years ago indicating rapid extinction. A crater has been identified showing that a large object capable of causing rapid extinction hit the Earth around the time of the sudden disappearance of the dinosaurs. Next >

29. Question 4 What evidence is there showing that there was a sudden mass extinction of the dinosaurs? A) The environment changed meaning rocks no longer fossilized creatures B) Dinosaurs were found to have evolved into other creatures C) Dinosaurs could not adapt to climate change D) The fossil record shows an abrupt end to dinosaur fossils 65 million years ago Next >

30. Question 4 What evidence is there showing that there was a sudden mass extinction of the dinosaurs? A) The environment changed meaning rocks no longer fossilized creatures B) Dinosaurs were found to have evolved into other creatures C) Dinosaurs could not adapt to climate change D) The fossil record shows an abrupt end to dinosaur fossils 65 million years ago Next >

31. Summary In this presentation you have seen: • how scientists analyze and evaluate explanations in science End >