During sea level transgressions, continental shelves are covered by water, and available habitats are enlarged, increasing the diversity of fauna. Transgressions are generally associated with greater diversification of species. Regressions cause extinctions through loss of environments, both shallow marine and beach. There is a close association between Pha-nerozoic extinctions and sea level low stands. Salinity fluctuations also affect diversity—the formation of evaporites (during supercontinent dispersal) causes reduction in oceanic salinity. For instance, Permian-Triassic rifts formed during the breakup of Pangaea had lots of evaporites (up to 4.4 miles, or 7 km thick), which lowered the salinity of oceans.
supercontinents affect the supply of nutrients to the oceans, and thus, the ability of life to proliferate. Large supercontinents cause increased seasonality, and thus lead to an increase in the nutrient supply through overturning of the ocean waters. During breakup and dispersal, smaller continents have less seasonality, yielding decreased vertical mixing, leaving fewer nutrients in shelf waters. seafloor spreading also increases the nutrient supply to the ocean; the more active the seafloor spreading system, the more interaction there is between ocean waters and crustal minerals that get dissolved to form nutrients in the seawater.
See also greenhouse effect; ice ages; plate tectonics.
de Wit, Maarten J., Margaret Jeffry, Hugh Bergh, and Louis Nicolaysen. Geological Map of Sectors of Gond-wana Reconstructed to Their Disposition at ~150 Ma. Tulsa, Okla.: American Association of Petroleum Geologists, Map Scale 1:10,000,000, 1988. Hoffman, Paul F. "Did the Breakout of Laurentia Turn Gondwana Inside-out?" Science 252 (1991): 1,409-1,412.
Kusky, Timothy M., Mohamed Abdelsalam, Robert Tucker, and Robert Stern, eds., Evolution of The East African and Related Orogens, and the Assembly of Gondwana. Precambrian Research, 2003. Murphy, J. Brendan, and Richard Damian Nance. "Mountain Belts and the Supercontinent Cycle." Scientific American 266, no. 4 (1992): 84-91. Rogers, J. J. W., and M. Santosh. Continents and Supercontinents. Oxford: Oxford University Press, 2004.
supernova Supernovas are extremely luminous stellar explosions associated with large bursts of radiation that can exceed the brightness of the entire galaxy it is associated with for a period of weeks or months. The energy released in a supernova event can exceed the amount of energy produced by the Earth's Sun over its entire life span. In these stellar explosions material is expelled from the core star at speeds of about one-10th the speed of light and is associated with a shock wave that moves through the interstellar medium, sweeping up an expanding shell of gas and dust that is known as a supernova remnant. A nova is a general name for a type of star that vastly increases in brightness (by up to 10,000 times) over very short periods of time, typically weeks. The word nova comes from the Latin for "new" and stems from early astronomers who thought that nova were new stars appearing in the sky, since the parent stars were too faint to be observed from the Earth before powerful telescopes were invented. The term nova is used for any star that increases rapidly in brightness by ejecting some of its material in the form of a cloud, whereas supernova are associated with stellar explosions, and are much more, even millions of times as luminous and energetic as nova.
Several different types of supernovas have been identified. The most common type is produced when a massive star ages and stops generating energy from nuclear fusion because it has spent all of its fuel. The massive star can undergo sudden gravitational collapse to form a neutron star or black hole, releasing
Kepler's supernova taken from combined data from Hubble Telescope, Spitzer Telescope, and Chandra X-Ray Observatory (NASA Marshall Space Flight Center)
huge amounts of gravitational potential energy that heats up and then expels the star's outer layers. A second type of supernova forms when a white dwarf star accumulates enough material from a stellar companion, typically in a binary star system, to raise the core temperature enough to start fusion of carbon, which forms a runaway nuclear fusion reaction, causing the star to explode. This may happen after the white dwarf has gone through hundreds of smaller nova events, each time exploding away an outer shell of gas, but leaving some behind that eventually contributes to the final, death-blow supernova explosion of the entire star.
A supernova event occurs about once every 50 years in the Milky Way Galaxy and other galaxies of similar size. The expanding shock waves from supernovas play an important role in synthesizing heavier elements and in triggering the formation of new stars.
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