Chapter #2 Impacts, Extinctions, and the Earliest History of Life on Earth.

1. Are the lunar mare light or dark colored features on the moon surface? How far back do these features date? (page 16)

2. Are the lunar highlands generally younger or older than the mare? What features are the highlands covered with? (page 16)

3. Why would the early Earth have experienced a larger impact rate than that of the moon? (page 16 and 27)

4. At what time did the Earth and Moon first start to experience a substantial decline in the impact rate? (page 16)

5. What is the estimated size of the asteroid that impacted Earth and is thought to have brought about the extinction of the dinosaurs? (page 19)

6. Approximately, how many known impact craters are there on the surface of the Earth? What is there range in size? (page 19)

7. What two geological periods are separated at the K/T boundary? Does the number of fossils found in the rock increase or decrease as you cross the K/T boundary, ? (page 20)

8. Which life forms were seen to change in abundance after the event that makes the K/T boundary? (page 20)

9. What types of elements or minerals are used to identify the cause of K/T boundary? How are these elements used? (page 20-21)

10. How large is the crater that corresponds to the impact that caused the K/T boundary? Where is it located? (page 21)

11. What is the minimum velocity an object can have when colliding with the Earth? How is this number arrived at (calculated)? (page 21)

12. Describe the environmental conditions that occur during a "nuclear winter" resulting from a large asteroid impact. How might these conditions affect life on Earth? (page 23)

13. Describe the power law which relates the size of asteroids to the number of asteroid impacts. (page 25)

14. How many asteroids are currently thought to be in Earth crossing or nearly Earth crossing orbits? (page 25)

15. What has happened on Earth to erase the record of the Earth's earliest impacts? (page 27)

16. Approximately how large of an object is required to eject enough debris to provide the energy necessary to evaporate the Earths oceans? Approximately how long would it take after an impact of this magnitude for the water vapor in the Earth's atmosphere to cool sufficiently to condense back into oceans? (page 30)

17. Define what is meant by the ocean's "photic zone"? How large an object is required to vaporize the photic zone? How might such an impact devastating to the early development of life on Earth? (page 30)

18. What are the names of the four objects in the asteroid belt that would be capable of evaporating the oceans if they were to impact Earth? (page 31)

19. Approximately when did Earth first become continuously habitable? (page 31)

20. What affect do Jupiter and Saturn have on the number of asteroids that are present in the inner solar system? According to Jakosky, how might the impact rate of the planets in the inner solar system be affected in Jupiter and Saturn were not present? (page 33)