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 lifeforms,
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 have profound
influences on 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 may increase.
Tectonics and supercontinent dispersal breaks apart and
separates 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 Permian) occurred with the formation of a supercontinent
(Pangea), sea-level regression, evaporite formation, and
global warming. At the boundary between the Permian and
Triassic periods and between the Paleozoic and Mesozoic
periods (245 million years ago), 96 percent of all species
became extinct. Lost were 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 half a mile thick over an area of 210,000 square miles
(547,000 km2) but have been 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 one million years
(remarkably short!) 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. It has
been postulated that the rapid volcanism and degassing
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 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 wildly fluctuating climate extremes.
Continental breakup may cause physical isolation of
species that cannot swim or fly between the diverging continents.
Physical isolation (via tectonics) produces adaptive
radiation-continental dispersal and thus increases biotic
diversity. For example, mammals had an explosive radiation
(in 10–20 million years) in the Paleocene-Eocene, right after
breakup of Pangea.
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