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Name: John
Status: Other
Age: 50s
Location: N/A
Country: N/A
Date: N/A 

I can compress dirt and it becomes warm but begins cooling instantly. After 4.5 billion years, wouldn't all of that heat be dispersed?
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 thermodynamics.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois

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