Rodinia
Rodinia (from the Russian родина, rodina, meaning "motherland, birthplace"[1][2][3]) was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.90 billion years ago (Ga)[4] and broke up 750–633 million years ago (Ma).[5] Valentine & Moores 1970 were probably the first to recognise a Precambrian supercontinent, which they named "Pangaea I."[5] It was renamed "Rodinia" by McMenamin & McMenamin 1990 who also were the first to produce a reconstruction and propose a temporal framework for the supercontinent.[6]
Not to be confused with Rhodinia, a genus of moth.
Rodinia formed at c. 1.23 Ga by accretion and collision of fragments produced by breakup of an older supercontinent, Columbia, assembled by global-scale 2.0–1.8 Ga collisional events.[7] Rodinia broke up in the Neoproterozoic with its continental fragments reassembled to form Pannotia 633–573 Ma. In contrast with Pannotia, little is known about the configuration and geodynamic history of Rodinia. Paleomagnetic evidence provides some clues to the paleolatitude of individual pieces of the Earth's crust but not to their longitude, which geologists have pieced together by comparing similar geologic features, often now widely dispersed.
The extreme cooling of the global climate around 717–635 Ma (the so-called Snowball Earth of the Cryogenian period) and the rapid evolution of primitive life during the subsequent Ediacaran and Cambrian periods are thought to have been triggered by the breaking up of Rodinia or to a slowing down of tectonic processes.[8]
Influence on paleoclimate and life[edit]
Unlike later supercontinents, Rodinia would have been entirely barren. Rodinia existed before complex life colonized on dry land. Based on sedimentary rock analysis, Rodinia's formation happened when the ozone layer was not as extensive as it is today. Ultraviolet light discouraged organisms from inhabiting its interior. Nevertheless, its existence did significantly influence the marine life of its time.
In the Cryogenian, Earth experienced large glaciations, and temperatures were at least as cool as today. Substantial areas of Rodinia may have been covered by glaciers or the southern polar ice cap. Low temperatures may have been exaggerated during the early stages of continental rifting. Geothermal heating peaks in crust about to be rifted; and since warmer rocks are less dense, the crustal rocks rise up relative to their surroundings. This rising creates areas of higher altitude, where the air is cooler and ice is less likely to melt with changes in season, and it may explain the evidence of abundant glaciation in the Ediacaran.[1]
The rifting of the continents created new oceans and seafloor spreading, which produces warmer, less dense oceanic crust. Lower density, hot oceanic crust will not lie as deep as older, cool oceanic lithosphere. In periods with relatively large areas of new lithosphere, the ocean floors come up, causing the sea level to rise. The result was a greater number of shallower seas.
The increased evaporation from the larger water area of the oceans may have increased rainfall, which in turn increased the weathering of exposed rock. By inputting data on the ratio of stable isotopes 18O:16O into computer models, it has been shown that in conjunction with quick weathering of volcanic rock, this increased rainfall may have reduced greenhouse gas levels to below the threshold required to trigger the period of extreme glaciation known as Snowball Earth.[24] Increased volcanic activity also introduced into the marine environment biologically active nutrients, which may have played an important role in the development of the earliest animals.