Most scientists who dispute the impact theory suggest that increased volcanic activity could have produced more sulfurous gases. These would reflect incoming solar radiation and cause global cooling. Alternatively, the intense volcanic activity might have released more carbon dioxide and water, resulting in global warming. The theory of increased volcanic activity is supported by the evidence of 65 million year-old lava deposits, which cover an area of 2.5 million square kilometres in what is now western India.
Climate change might well have been a major contributory factor in eradicating this formidable group of animals. A meteor impact would have produced effects over a short time span whereas increased volcanic activity would have caused disruption over longer periods. Some scientists think that the most likely cause of the mass extinction of the dinosaurs was long-term environmental change due to increased volcanic activity accompanied by a meteor impact, resulting in a rapid decline at the beginning of the Tertiary era.
Q3 Summarise the alternative explanation for the cause of the mass extinction of the dinosaurs presented in the preceding passage.
Q4 Is it possible to conclude which of the two theories (meteorite strike or volcanic activity) is more likely to be correct? If not, why not?
Q5 Considering the facts presented, and using your own knowledge and background reading, state which theory of extinction you favour and give the facts supporting your argument.
To find out more about dinosaurs and which ancient reptiles were not dinosaurs, visit the dinosaur pages of the Smithsonian Institute website and the Discovering Dinosaurs website where you can find masses of fascinating dinosaur facts (see the weblinks for this extension).
Salters-Nuffield Advanced Biology Resources
Safety checked, but not trialled by CLEAPSS. Users may need to adapt the risk assessment information to local circumstances. Extension 5.5 Teacher Sheet
VICTIMS OF CLIMATE CHANGE?
Purpose
The aim of this extension is to consider the idea that there can be alternative explanations for a scientific observation, in this case the extinction of the dinosaurs. There have been many explanations proposed for this mass extinction. However, scientists consider that only a few are supported by evidence. The favoured theories suggest that climate change was involved in the mass extinction of dinosaurs.
Answers
Q1 The first two theories described are plausible, but it is very difficult to see how they can be tested. They also do not explain the mass extinction of other species that occurred at the same time. Theory C, that a meteor hit the Earth and caused temporary global cooling, can be tested by looking for evidence of the impact. The theory can also explain the extinction of other species at the same time. Some species would have survived at places distant from the impact zone. Some species may have been able to cope with the cold conditions.
Q2 Dating events that occurred millions of years ago is not very accurate. The incomplete fossil record means we cannot be sure if the dinosaurs all disappeared within a year or two across the globe or if their extinction took place over a much longer period of time.
Q3 Increased volcanic activity could have resulted in the mass extinction. It may have produced more sulfurous gases, reflecting incoming radiation, causing global cooling. Alternatively, it may have resulted in the release of more carbon dioxide and water, causing global warming. The evidence for increased volcanic activity is the large lava deposits in western India. Q4 At present it is not possible to conclude which of the two theories is more likely to be correct
as evidence to discriminate between them is lacking. That is why the two theories exist side- by-side in the scientific community at this time.
Q5 What matters here is the quality of the argument and the supporting facts. They can argue for either of the previous theories, or an entirely different one if they can support the argument with data from reliable sources.
If available, students could watch the last five minutes of the final episode of the BBC series Walking with Dinosaurs (Episode 6), from just after the point when the T. rex chick dies. They could then answer the questions below:
Q1 At what point on the Earth’s surface did the giant meteor hit the Earth? Q2 What do you think killed the dinosaurs in this area?
Q3 Do you think all the dinosaurs on Earth were killed in the same way? Explain your reasons. Q4 Which group of dinosaurs escaped extinction?
Answers
Q1 Gulf of Mexico.
Q2 The burst of thermal radiation associated with the explosive impact.
Q3 Those at a distance would not have been killed by the heat of the direct explosion, but by the shock wave and clouds of dust and debris. These may have had a direct effect on the dinosaurs or might have caused environmental changes that subsequently killed the dinosaurs.