Due Wed, January 28, 1998

Due at the beginning of class.  Must be typed, as per the syllabus.  To save you some time looking, the answer is not in the book (although some Physical Geology textbooks treat this subject).

Essay/Thought Question (5 pts):   As we discussed in class, because the lithosphere is cool and strong, it doesn't deform easily.  Heat, therefore, conducts out of the lithosphere at the surface -- and the lithosphere has a fairly steep geothermal gradient (25°C/km).  The geothermal gradient of the asthenosphere is much lower (about 1-2°C/km average down to the core).  Thus the core is not nearly as hot as one might expect from the temperature gradient near the surface.

Briefly explain: 1) why the earth is hot inside, 2) what process keeps the lower mantle and core from being too hot, and 3) what all this heat has to do with plate tectonics.
 
 
 

Grading Rubric (points awarded out of 5 possible):

5 pts = Well-written and grammatically correct sentences; answers or information is factually correct; depth of information is at a college level (not just very basic information).

4 pts = Work is substantially correct and well-written, although it may include one or more minor problems with presentation or with correctness of answers.

3 pts = Work includes one or more major problems with presentation or with correctness of answers.

2, or 1 pts = Work has substantial flaws in presentation and content.