Alright, kids, it's time for some crappy ASCII art:
V--- continental shelf
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\ <--continental slope
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\\ abyssal plain
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\\\ <--continental rise |
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\\\ V
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An abyssal plain is a large, relatively flat region of the ocean floor, at about 10,000-20,000 feet below sea level. They exist next to continents in the middle of ocean basins, covering roughly 25% of the sea bottom, interrupted by trenches, abyssal hills, underwater mountains, and contintental margins. They generally consist of large sedimentary areas known as turbidites, and are the flattest places on earth, having felt the unencumbered current of the ocean for over five billion years.
Evolutionists place great importance on the abyssal plains as a major breeding ground for some of life's earliest creatures - single-celled bottom-dwelling organisms, collectively referred to as the benthos. Even more importantly, in areas where deep sea vents and small rifts are common, archaea, chemautotrophic bacteria, and other small organisms grow at a rapid rate, feeding off the sulfur and nitrogen emitting from the earth's core. In turn, these creatures become food for sea worms and other bottom-dwelling life forms. This cycle of life, in theory, may have led to larger and larger aquatic creatures, and eventually to land dwellers.
Some of the more scientifically noteworthy abyssal plains include the Madeira Abyssal Plain off the coast of Spain; the Balearic Abyssal Plain in the Mediterranean; the Sohm Abyssal Plain off the eastern coast of Canada; and the Nares Abyssal Plain north of Puerto Rico.
Sources
- http://www.britannica.com/eb/article?eu=3481
- http://users.rcn.com/jkimball.ma.ultranet/ BiologyPages/O/Oceans.html
- http://www.jbpub.com/oceanlink/interactive_glossary_showterm.cfm?term=Abyssal%20plain