BOX 2.1 Continental Drift and Climate

Plate tectonics has been rearranging Earth’s configuration of continents ever since the plates on Earth became rigid approximately 2.5 billion years ago (Figure 2.1). On long (millions of years) timescales, the movement of tectonic plates—and the continents that ride upon them—has strongly influenced Earth’s distribution of solar insolation, ocean and atmospheric circulation, and carbon cycling between the Earth’s deep and shallow reservoirs, thereby profoundly impacting global climate, sea level, and the overall planetary ecology.

The arrangement of the continents through time is most reliable for the past 800 million years, the period for which the chronostratigraphic tools necessary for reconstructions are available. The global views presented in Figure 2.1 show how the continents on Earth’s surface may have appeared during four intervals of time that are noted throughout this report: the unipolar glaciated Pennsylvanian (300 million years ago [Ma]), mid-Cretaceous (105 Ma), Eocene (50 Ma), and mid-Pliocene (3 Ma).

The major transitions between climatic icehouse and greenhouse conditions are ultimately most probably driven by the deep Earth processes of plate tectonics, as a function of the long-term balance between CO2 degassing at spreading centers and the conversion of atmospheric CO2 to mineral carbon through long-term silicate weathering and oceanic carbonate formation (Berner, 2004). For example, the eruptions of large igneous provinces in the mid-Cretaceous and the subduction of the carbonate-rich tropical Tethys Sea in the early Cenozoic are the most likely cause of the high-CO2 equilibrium climates of the Cretaceous and Eocene greenhouses. Conversely, uplift of the Himalayas and Tibetan Plateau associated with “docking” of the Indian subcontinent with Asia (~40 Ma), and the evolution of vascular land plants in the early Paleozoic (~450 Ma), led to the sequestration of atmospheric CO2 through enhanced weathering of silicate minerals (Ruddiman, 2007; Archer, 2009).

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