Tremendous amounts of life were concentrated in the earth’s oceans because an aqueous environment is conducive to simple forms of life. Water provides a means of support, moisture, gamete transfer, and contains the essential nutrients and gases necessary for survival (Reader, Lecture 12). Much of the marine life was concentrated in the shallower areas of the oceans because of the constant movement of the water bringing food to filter feeding animals, and easy access to sunlight for photosynthesis.
If global sea levels drop, the habitable shallow areas for marine organisms are reduced, thereby causing extinctions in those marine habitats (Newton, 1989). It is generally understood that there is a correlation between habitable area and species diversity; therefore, less shallow water living area means fewer marine critters can survive (Brenchley, 1989). Also, because sea level is lowered and widespread unconformities occur on the continental margins, the volume of preserved marine sediment is low (Newton, 1989). This means that the sediments that marine organisms used and lived in washed away as well. Another consequence of global sea level drops is the elimination of interior seas. Interior seas, such as the modern day Black Sea, would have dried up and left salt deposits in their place and all of the marine organisms within it would have died (Ward, 1989)
Global sea level changes have been noted in all five mass extinction events. Global sea level drop occurred in the Late Ordovician, Late Permian, and Late Cretaceous extinctions. There is a global sea level rise in the Late Devonian and a minor drop in the Late Triassic (Newton, 1989). A major problem with citing sea level alterations, especially lowering of global sea level, is that the largest sea level drop occurred in the Cenozoic and it did not result in a mass extinction; in fact, very few marine organisms were affected. |
