March 21-27, 2013, Current Events Lesson Plan
Current Event:
Scientists recently announced that the object that smashed into Earth 65 million years ago, leading to a mass extinction that included the dinosaurs, may have been a comet, not an asteroid. Scientists have long thought that the object whose impact wiped out nearly all large animals was a huge, relatively slow-moving asteroid. This belief was based in part on the large amount of the chemical iridium in the stratum of Earth called the Cretaceous-Paleogene Boundary. This chemical element is very rare in Earth’s crust but is common in such space bodies as asteroids and meteorites. Scientists believe that the impact of the large asteroid created the Chicxulub crater in Mexico’s Yucatan Peninsula, which dates to the same geologic time period as the iridium layer. However, Jason Moore, a paleoecologist at Dartmouth College, recently presented findings that the iridium levels in the Chicxulub crater are lower than originally reported. This suggests that the impactor was smaller than previously believed. Dr. Moore theorizes that a body that could leave such small amounts of iridium but such a huge crater could not be a large asteroid. He thinks the impactor was actually a small, fast-moving comet.
Objective:
For about 160 million years, dinosaurs were the largest and most successful vertebrates on land. Then about 65 million years ago, dinosaurs died out along with many other large animals. Mammals thereafter became the world’s dominant land vertebrates. Scientists have developed many theories to explain dinosaur extinction. The two major theories involve (1) the collision of an asteroid (or comet) with Earth and (2) large volcanic eruptions in what is now India. The leading theory holds that the mass extinction was caused by the impact of a large asteroid (or comet) in present-day Mexico. The asteroid (or comet) impact threw billions of tons of dust and debris into the atmosphere, may have caused huge fires worldwide, and blocked sunlight from reaching the surface of Earth for many months. Because such a catastrophe would have been severe and widespread, plant-eating dinosaurs would have starved to death. As the plant-eaters died, so did the meat-eating dinosaurs that fed on them. The other major theory is that the mass extinction followed volcanic eruptions in present-day India that created huge lava beds and released large volumes of gas, causing rapid climate change. Many scientists think that a combination of causes contributed to the extinction of the dinosaurs. The Behind the Headlines news story and related World Book articles explore the world of dinosaurs and discusses how they may have died out.
Words to know:
- Luis Alvarez
- Asteroid
- Chicxulub crater
- Comet
- Dinosaur
- Extinction
- Fossil
- Iridium
- Paleontology
- Prehistoric animal
- Stegosaurus
- Triceratops
- Tyrannosaurus
- Volcano
Discussion Topics:
1. Ask your students to name some types of dinosaurs. [They might name the Apatosaurus (formerly called Brontosaurus); Brachiosaurus; Iguanodon; Stegosaurus; Triceratops; Tyrannosaurus.]
2. Ask your students how scientists use the scientific method to conduct research. [The scientific method is: (1) identify a problem; (2) gather all the pertinent data; (3) formulate a hypothesis; (4) perform experiments; (5) interpret the results; and (6) draw conclusions.]
3. Have your students review World Book’s Fossil article. Ask your students how scientists use fossils to obtain information about dinosaurs. (They might say that scientists learn about the appearance of dinosaurs; how dinosaurs lived and behaved.)
4. Ask your students to debate, “If scientists were able to resurrect dinosaurs or other extinct animals by cloning or other methods, should they do it?”
5. Ask your students to use World Book’s Timelines feature to create a timeline of dinosaur discoveries. (Students may wish to use the Dinosaur discoveries section of World Book’s Dinosaur article for help.)