Page 97 - Earth's Climate Past and Future

CHAPTER 4 • Plate Tectonics and Long-Term Climate 73

FIGURE 4-17 Age of the seafloor
Some ocean crust dates as far back as
175 Myr ago. Modern spreading rates
are as much as ten times faster in the
Pacific than in the Atlantic. (Modified
from S. Stanley, Earth System History, ©
1999 by W. H. Freeman and Company,
after W. C. Pitman et al., Map and Chart
Series MC–6 [Boulder, CO: Geological
Society of America, 1974].)

Age 0–5 5–21 21–38 38–52
(Myr) 52–65 65–140 140–160 > 160

Warm
Rapid greenhouse
CO input climate
2
Fast seafloor (increased temperature,
spreading rain, vegetation)
Reduced
warming
Increased
chemical
weathering

Increased
CO removal
2

Cold FIGURE 4-18 The spreading rate
Slow icehouse (BLAG) hypothesis This hypothesis
CO input
2
Slow seafloor climate predicts that atmospheric CO 2
spreading (decreased temperature, concentrations and global climate are
rain, vegetation)
driven by the global mean rate of
Reduced seafloor spreading, which controls the
cooling rate of CO input at ocean ridge crests
2
Decreased and subduction zones. The spreading
chemical rate hypothesis also invokes chemical
weathering weathering as a negative feedback
that partially counters changes in
Decreased atmospheric CO and global climate
CO removal 2
2 initiated by varying rates of seafloor
spreading.