I think nuclear reaction of the atom in the center of the Earth or even the center of Venus happens because the atom is unstable in those locations.
As we have already mentioned before, the position of the atom in a mass is important: atoms with more bonds have less free energy than those with less bonds.
<b>This is what Gravity is about.</b>
Venus' higher heat flow from the interior is directly imputed to this: -its position in the solar system.
I am assuming that the solar system is moving towards the ecliptic of the galaxy. This region is at a higher entropy state.
This is the reason why temperatures (for all atoms in the solar system)will increase gradually until the solar system crosses this region after which cooling will be the trend.
WHAT ELSE CAN THIS BE ATTRIBUTED TO ?
There were no Co2 emitting industrial factories 500 000 years ago on Earth for past warming and cooling cycles!
There are no factories on Venus either !
Jim, I have found some interesting information on heat flows for which recent data was taken from bore holes. These indicate a long term warming trend which started prior to industrialization:
www.geo.lsa.umich.edu/~shaopeng/2004GL019781.pdf
You might question the information taken before the 1900's. Maybe we will have to wait another few 100 years in order to get reliable info.
....I know I won't be around to see this, because the atoms in my body are also affected by time (therefore position).
