Essay Questions
 

1. Name three tectonic plates.
 
 Eurasian Philippine Australian Pacific Cocos Jan De Fuca
 North American Nazca Caribbean Antarctic S. American
 Scotia Eurasian Arabian African Indian
 
 
2. 200 million years from now, where would you imagine Antarctica to be located?
 
 We would expect Antarctica to remain where it is.  This is because Antarctica is on its own plate and is not being effected by any other plates.  It has remained in relatively the same position for millions of years.
 
 
3. What are the 4 types of plate boundaries?
 
 Divergent boundaries -- where new crust is generated as the plates pull away from each other.
 Convergent boundaries -- where crust is destroyed as one plate dives under another.
 Transform boundaries -- where crust is neither produced nor destroyed as the plates slide horizontally past each other.
 Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.
 
 
4. Are continents "recycled"?  How?
 
 This question particularly intrigued Harry H. Hess, a Princeton University geologist and a Naval Reserve Rear Admiral, and Robert S. Dietz, a scientist with the U.S. Coast and Geodetic Survey who first coined the term seafloor spreading. Dietz and Hess were among the small handful who really understood the broad implications of sea floor spreading. If the Earth's crust was expanding along the oceanic ridges, Hess reasoned, it must be shrinking elsewhere. He suggested that new oceanic crust continuously spread away from the ridges in a conveyor belt-like motion. Many millions of years later, the oceanic crust eventually descends into the oceanic trenches -- very deep, narrow canyons along the rim of the Pacific Ocean basin. According to Hess, the Atlantic Ocean was expanding while the Pacific Ocean was shrinking. As old oceanic crust was consumed in the trenches, new magma rose and erupted along the spreading ridges to form new crust. In effect, the ocean basins were perpetually being "recycled," with the creation of new crust and the destruction of old oceanic lithosphere occurring simultaneously. Thus, Hess' ideas neatly explained why the Earth does not get bigger with sea floor spreading, why there is so little sediment accumulation on the ocean floor, and why oceanic rocks are much younger than continental rocks.
 
 
5. How is energy provided to organisms that live along trenches in the deep ocean?

Since 1977,  hot springs and associated sea life have been found at a number of sites along the mid-oceanic ridges, many on the East Pacific Rise. The waters around these deep-ocean hot springs, which can be as hot as 380 °C, are home to a unique ecosystem.  Detailed studies have shown that hydrogen sulfide-oxidizing bacteria, which live symbiotically with the larger organisms, form the base of this ecosystem's food chain. The hydrogen sulfide (H2S--the gas that smells like rotten eggs) needed by these bacteria to live is contained in the volcanic gases that spew out of the hot springs. Most of the sulfur comes from the Earth's interior; a small portion (less than 15 percent) is produced by chemical reaction of the sulfate (SO4) present in the sea water. Thus, the energy source that sustains this deep-ocean ecosystem is not sunlight but rather the energy from chemical reaction (chemosynthesis).