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2. Dinosaurs became extinct at the end of the Cretaceous Period. Experts disagree about what caused their extinction. Some believe THEORIES that say extinction happened very quickly, and others believe a gradual process was responsible. The extinction event that killed the dinosaurs affected the entire earth! Some plants and animals on land and in water became extinct. Other plant and animals groups did not become extinct. Fish, turtles, crocodilians, birds and mammals survived. Scientists use the fossil record to find reasons for all extinctions. Read some of the theories. What do you think? Next

3. What Happened to the Dinosaurs? Explore some EXTINCTION theories. GIANT IMPACTVOLCANOES DISEASEMAMMALS Finish

4. A giant asteroid strikes Earth. Giant waves sweep over Earth, fires start all over the world and huge clouds of dust spread into the atmosphere. Algae in oceans and plants on land die with no sunlight. Chemicals from the asteroid poison rivers, lakes and oceans. Dinosaurs die quickly from fire, storm, poison and starvation. BACK

5. In this theory, dinosaurs did not become extinct suddenly. Huge volcanoes erupt, cover the land with lava and fill the air with huge clouds of dust. The weather changes between unusually hot and cold. Plants die over long periods of time. The plant-eaters died, followed by meat-eaters like T- Rex. By the time the eruptions stopped, many plants and animals, including dinosaurs, were gone. BACK

6. One theory suggests that disease caused the dinosaurs to become extinct. Modern reptiles and amphibians become infected and get diseases. If animals don’t get the right kind of food, they suffer diseases. Diseases can be spread by insects. Could diseases like these have caused the extinction of dinosaurs? BACK

7. Mammals eating dinosaurs' eggs has been suggested as a cause of dinosaur extinction. Animals that ate one particular dinosaur's eggs (more than others) may have prevented any eggs from that species from hatching. The result would be that that dinosaur would die out. If every egg of a species was destroyed, there would be no more dinosaurs of that species. BACK

8. Talk about the problems with each theory. After you have considered all the theories, decide which one you think is most likely. Record the theory on your paper with a picture. Give reasons for your decision. BACK