Re: Which radioactive isotopes create the internal heat of the earth?

Hi Richard,

Radioactive elements such as uranium, thorium, and potassium are low 
abundance in the Earth, but they pack quite a punch!  When radioactive 
elements decay, they emit atomic particles that collide with and are 
absorbed by the surrounding matter.  This stops the particles from moving, 
and the energy of motion changes to heat energy.  There is enough heat 
energy generated by radioisotope decay to cause convection within the Earth 
and continental drift of the crust.  

When a planet accretes (when pieces of matter accumulate into a larger 
body), energy is emitted by the when pieces of matter collide and 
subsequently accumulate.  Though this generates a great deal of energy, 
most of this energy has already dissipated from the Earth's interior.  
Presently, radioactive isotope decay is the primary source of heat energy 
in the Earth's interior.  Moreover, the moon probably does not cause much 
tidal heating of the Earth.  The Earth should have much more of an effect 
on the moon because it is much larger, but since the moon is geologically 
dead this does not matter.  

Good luck on your paper.  If you need more information, please feel free to 
write back.

Sarah Earley
CU Boulder