Plate Tectonics Supercontinents And Life

Plate tectonic motions, especially the supercontinent cycle, profoundly affect the distribution and evolution of life on Earth. Plate tectonic activity such as rifting, continental collision, and drifting continents affects the distribution of life-forms, the formation and destruction of ecological niches, and radiation and extinction blooms. Plate tectonic effects also can induce sea level changes, initiate periods of global glaciation, change the global climate from hothouse to icehouse conditions, and affect seawater salinity and nutrient supply. All of these consequences of plate tectonics profoundly influence life on Earth.

Changes in latitude brought on by continental drift bring land areas into latitudes with better or worse climate conditions. This has different consequences for different organisms, depending on their temperature tolerance, as well as food availability in their environment. Biological diversity generally increases toward the equator, so, in general, as continents drift poleward more organisms tend to go extinct, and as they drift equatorward, diversification increases.

Tectonics and supercontinent dispersal break apart and separate faunal provinces, which then evolve separately. Continental collisions and supercontinent amalgamation build barriers to migration but eventually bring isolated fauna together. One of the biggest mass extinctions (at the end of the Permian) occurred with the formation of a supercontinent (Pangaea), sea level regression, evaporite formation, and global warming. At the boundary between the Permian and Triassic Periods and between the Paleozoic and Mesozoic Periods (250 million years ago), 70-90 percent of all species became extinct. Casualties included the rugose corals, trilobites, many types of brachiopods, and marine organisms including many foraminifer species.

The Siberian flood basalts cover a large area of the central Siberian Plateau northwest of Lake Baikal. They are more than one-half mile thick over an area of 210,000 square miles (547,000 km2) but have significantly eroded from an estimated volume of 1,240,000 cubic miles (3,3133,000 km3). They were erupted over a period of less than 1 million years, 250 million years ago at the end of the Permian at the Permian-Triassic boundary. They are remarkably coincident in time with the major Permian-Triassic extinction, implying a causal link. The Permian-Triassic boundary at 250 million years ago marks the greatest extinction in Earth history, where 90 percent of marine species and 70 percent of terrestrial vertebrates became extinct. The rapid volcanism and degassing could have released enough sulfur dioxide to cause a rapid global cooling, inducing a short ice age with associated rapid fall of sea level. Soon after the ice age took hold, the effects of the carbon dioxide that was also emitted by the volcanism took over and the atmosphere heated, resulting in a global warming. The rapidly fluctuating climate postulated to have been caused by the volcanic gases is thought to have killed off many organisms, which were simply unable to cope with the wild climate changes.

Continental breakup can physically isolate species that cannot swim or fly between the diverging continents. Physical isolation (via tectonics) produces adaptive radiation—continental dispersal thus increases biotic diversity. Mammals had an explosive radiation (in 10-20 million years) in the Paleocene-Eocene, right after breakup of Pangaea.

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