Super continents

In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some earth scientists use a different definition, "a grouping of formerly dispersed continents", which leaves room for interpretation and is easier to apply to Precambrian times although at least about 75% of the continental crust then in existence has been proposed as a limit to separate supercontinents from other groupings.

Supercontinents have assembled and dispersed multiple times in the geologic past (see table). According to modern definitions, a supercontinent does not exist today. The supercontinent Pangaea is the collective name describing all of the continental landmasses when they were most recently near to one another. The positions of continents have been accurately determined back to the early Jurassic, shortly before the breakup of Pangaea (see animated image). The earlier continent Gondwana is not considered a supercontinent under the first definition since the landmasses of Baltica, Laurentia and Siberia were separate at the time. Supercontinents appear to form by two end-member processes: extroversion, in which the oceanic lithosphere surrounding the supercontinent (exterior ocean) is preferentially subducted (e.g. Pannotia), and introversion in which the oceanic lithosphere formed between dispersing fragments of the previous supercontinent (interior ocean) is preferentially subducted (e.g. Pangea). Extroversion can be explained by “top–down” geodynamics, in which a supercontinent breaks up over a geoid high and amalgamates above a geoid low. Introversion, on the other hand, requires that the combined forces of slab-pull and ridge push (which operate in concert after supercontinent break-up) must be overcome in order to enable the previously dispersing continents to turn inward. As Eurasia moves laterally along the Ring of Fire, it will eventually collide with the Americas, forming a new supercontinent in the next 50 million to 200 million years.

                                   

                 Image via- en.wikipedia.org 

     

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