Earth's Internal Heat
I can compress dirt and it becomes warm but begins cooling
instantly. After 4.5 billion years, wouldn't all of that heat be
How hot would the earth have had to have been 4.5 billion
years ago to still be this hot at the center or is there some continually
"fueling" process that has also defied the second law of thermodynamics?
You are quite correct, the current heat of the earth's core is not leftover
heat from the formation of the earth. As you guessed, the earth's interior
would have cooled off by now if there weren't some source of energy. That
source happens to be radioactive decay of elements such as uranium. This
process continually heats the earth, and does not defy the second law of
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
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Update: June 2012