The continents appear to have collided about every five hundred million years and formed vast supercontinents. A number of supercontinents have been proposed: Vaalbara (3636–2803 mya), Ur (2803-2408 mya) Kenorland (2720-2114 mya) and Columbia (1820-1350 mya). During the Proterozoic there were two successive supercontinents: Rodinia (1130-750 mya) and Pannotia (633-573 mya). Pannotia fragmented into Gondwana (South America, Africa, India, South China, Australia and Antarctica); Laurentia (North America and Greenland), Baltica (Europe); and Siberia.
During the Early Palaeozoic, Gondwana (the core of Pannotia) slowly drifted across the South Pole while Laurentia, Siberia and Baltica moved towards the equator. During the Silurian, Baltica joined with Laurentia to form the larger continent Euramerica (=Laurussia) which with the addition of further landmasses during the Carboniferous became the major continent Laurasia.
Throughout the Carboniferous, Laurasia (north) and Gondwana (south) moved towards each other, a process that ended in the Permian with the formation of the ‘C’ shaped supercontinent Pangaea (336-175 mya): the western edges of the two landmasses having collided obliquely, leaving the eastern edges separated by the Tethys Sea and open in the east to the global ocean Panthalassa. Pangaea began to break up in the Jurassic; first into the two great continents Laurasia (north) and Gondwana (south), and then progressively into the continents we have today.
During the 1970s James W. Valentine (1926- ) and Eldridge M. Moores (1938- ) suggested that because tectonic plate movement affected geography, it could also affect climate and faunal changes. Valentine showed how the forming and rifting of continents explained changing taxonomic diversity over major timescale boundaries and that this could explain important parts of the extinction record. Jack John Sepkoski (1948-99) and David M. Raup (1933-2015) suggested that the extinction of dinosaurs was part of a cycle of mass extinctions that may have occurred about every twenty-six million years.
In 1981 Sepkoski identified the three great evolutionary faunas in the marine animal fossil record: the Cambrian, Palaeozoic and Cenozoic, each composed of classes of animals having broadly similar ecologies. Most importantly, they se-quentially replaced one another as dominant groups over the span of the geological periods.
The exact causes for ice ages, and the glacial cycles within them, have not been proven. They are most likely the result of a complicated dynamic interaction between such things as position and height of the continents, ocean circulation, composition of the atmosphere, solar output and the distance of Earth from the Sun.
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