Page 83 - Earth's Climate Past and Future

CHAPTER 4

Plate Tectonics and

Long-Term Climate

The last 550 Myr of Earth’s history are far better known than the first 4 billion
years. From this time forward, the locations of the continents and the shapes of
the ocean basins become progressively clearer. Better-preserved sedimentary
rock archives also hold more abundant evidence of past climates, including
alternations between icehouse intervals (when ice sheets were present)
and greenhouse intervals (times without ice on land). These fluctuations
(Figure 4-1) are the focus of this chapter.
First we examine how plate tectonic processes work. Next we explore the
possibility that icehouse intervals occur because plate tectonic motions cause
continents to drift across cold polar regions. Then we use climate models to
investigate the range of factors that controlled climate 200 Myr ago, a time
when all landmasses on Earth existed as a single giant continent. These investi-
gations reveal that changes in atmospheric CO levels are needed to explain
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the sequence of changes from icehouse to greenhouse conditions over the last
half-billion years. Finally we evaluate two hypotheses that link changes in plate
tectonic processes to changes in CO levels.
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