Answers to Textbook Review Questions

1. The Great Lakes formed when the North American ice sheet melted and waters that drained from its southern border filled depressions left behind as the ice sheet retreated.
2. Fossil pollen reveals that individual species, rather than whole floras, migrated as the climate shifted during the retreat of continental glaciers. This indicates that assemblages of species were temporary and were reshuffled as the climate changed. For example, the transitional climate in North America supported an evergreen forest unlike any modern flora.
3. Fossil specimens of the reef-building "moosehorn" coral on the island of Barbados have been dated radiometrically. Since these corals always grows close to sea level, their fossils--obtained from cores drilled through the limestones of Barbados--indicate the level of the sea in relation to the island for various past intervals.
4. The large mammals that disappeared from North America between 12,000 and 11,000 years ago include the mammoth, woolly mammoth, and mastodon; a large beaver; five species of horses; three species of deer; two species of wild oxen and three of musk oxen; the North American camel; a large bison; two species of giant armadillos; and several species of large ground sloths. Several species of carnivores also went extinct: the short-faced bear, the dire wolf; a lion; a cheetah; and three species of large sabertooth cats.
5. Evidence favoring the idea that human hunters caused the extinction of large mammals includes the fact that hunters favor large animals as prey; large animals are especially conspicuous to hunters; extinctions of large animals were especially numerous in North and South America, where humans had recently arrived and animals may not have feared them; and the species of large North American herbivores that did not become extinct had recently migrated from Eurasia, where they had learned to fear human hunters.
6. Evidence favoring the idea that climate caused the extinction of large mammals includes the fact that the Younger Dryas interval began and ended suddenly and temperatures shifted abruptly; and certain habitats that had supported many large herbivores disappeared--the northern grassy region gave way to less nutritious prairies.
7. When the climate warmed and evaporation from warmer seas provided more moisture, snow accumulated more rapidly in Greenland. Thus, the thickness of the annual layers of glacial ice in Greenland provides a record of climatic change.
8. Because the Middle East, being nearer the equator, had a warmer climate than Europe and North America. Agriculture could not have spread throughout Europe until glacial and near-glacial conditions gave way to temperate climates.
9. Evidence of periods of dryness in various regions over the past 10,000 years includes fossils of lake-dwelling life and pollen in African lakes; satellite photography which shows that numerous dunes, now stabilized by vegetation, were active near the Colorado-Nebraska border four times within the past 10,000 years; analysis of tree rings on the western slope of the Sierra Nevada; and the exposure of ancient stumps in Mono Lake when the lake level dropped in 1940.
10. Conditions that have affect regional sea level over the past 7000 years include isostatic rebound of the crust resulting from the retreat of huge glaciers; subsidence of peripheral bulges (elevations of the crust around the margins of ice sheets) as a result of the melting of ice sheets; and glacial tectonic uplift in certain regions.

Answers to CD/Web Review Questions

1. True.
2. Continentality.
3. Africa.
4. No.
5. South America, Australia, Europe, Asia, and Africa.
6. 75 percent.
7. The elk, moose, and buffalo.
8. 2°F.
9. 2°F.
10. Because the cooling trend that marks the Little Ice Age began at different times in different parts of the world and often was interrupted by periods of relative warmth.
11. A regional warming trend over the past several decades.
12. A third.
13. Further global warming.
14. True.
15. 5 percent.