Page 104 - Earth's Climate Past and Future

80 PART II • Tectonic-Scale Climate Change

reduction in vegetation cover. A slowing of the rate of 6. What are the major characteristics of the climate
CO removal would leave more CO in the atmosphere of Pangaea?
2 2
and moderate the overall cooling. In the end, the uplift- 7. What is the central concept behind the BLAG
induced weathering increase would succeed in causing a (spreading rate) hypothesis?
net global cooling, but it would not be nearly so large a
cooling as would have occurred without the negative 8. What role does chemical weathering play in the
weathering feedback. BLAG hypothesis?
9. Write a chemical reaction showing how
IN SUMMARY, both the BLAG (spreading rate) weathering removes CO from the atmosphere.
2
hypothesis and the uplift weathering hypothesis seem 10. How soon after deposition does freshly
to provide plausible explanations of most major fragmented debris undergo most chemical
icehouse-greenhouse changes of climate (see weathering?
Tables 4–2 and 4–3). In Chapter 6 we will revisit both
hypotheses by examining in greater detail the sequence 11. Why is chemical weathering faster in the eastern
of changes from the warm greenhouse climate of Andes than in the Amazon lowlands?
100 Myr ago to the modern icehouse climate.
12. How could chemical weathering be both the driver
and the thermostat of Earth’s climate?

Key Terms

continental crust (p. 60) paleomagnetism (p. 62)
ocean crust (p. 60) magnetic lineations (p. 63) Additional Resources
mantle (p. 60) seafloor spreading Basic Reading
lithosphere (p. 60) (p. 64) Companion Web site at www.whfreeman.com/
asthenosphere (p. 60) polar position hypothesis ruddiman2e, pp. 3–11, 14–22, 27–30.
tectonic plates (p. 61) (p. 64) Advanced Reading
divergent margins Gondwana (p. 65)
(p. 61) Pangaea (p. 65) Berner, R. A. 1999. “A New Look at the Long-Term
Carbon Cycle.” GSA Today 9: 1–6.
convergent margins evaporite (p. 69) Blum, J. D. 1997. “The Effect of Late Cenozoic
(p. 61) red beds (p. 71)
Glaciation and Tectonic Uplift on Silicate
subduction (p. 61) spreading rate hypothesis Weathering Rates and the Marine 87Sr/86Sr
continental collision (p. 71) Record.” In Tectonic Uplift and Climate Change, ed.
(p. 62) hot spots (p. 71) W. F. Ruddiman. New York: Plenum Press.
transform fault margins uplift weathering Chamberlain, T. C. 1899. “An Attempt to Frame a
(p. 62) hypothesis (p. 75) Working Hypothesis of the Cause of Glacial
magnetic field (p. 62) mass wasting (p. 77) Periods on an Atmospheric Basis.” Journal of Geology
7: 545–84, 667–85, 751–87.
Kutzbach, J. E. 1994. “Idealized Pangaean Climates:
Sensitivity to Orbital Parameters.” Geological Society
Review Questions of America Special Paper 288: 41–55.
Parrish, J. T., A. M. Ziegler, and C. R. Scotese. 1982.
1. Does each lithospheric plate correspond to an “Rainfall Patterns and the Distribution of Coals and
individual continent or ocean basin? Evaporites in the Mesozoic and Cenozoic.”
Palaeogeography, Palaeoclimate, Palaeoecology 40:
2. What kind of physical behavior in Earth’s deeper 67–101.
layers allows the plates to move?
Raymo, M. E., W. F. Ruddiman, and P. N. Froelich.
3. Explain how paleomagnetism tells us about past 1986. “Influence of Late Cenozoic Mountain Building
latitudes of continents. on Ocean Geochemical Cycles.” Geology 16: 649–53.
Stallard, R. F., and J. E. Edmond. 1983. “Geochemistry
4. Explain how paleomagnetism tells us about rates of of the Amazon 2: The Influence of the Geology
spreading at ocean ridges.
and Weathering Environments on the
5. Do glaciations always occur when continents are Dissolved Load.” Journal of Geophysical Research 88:
located in polar positions? 9671–88.