Heat flow from a differentiated Earth

Calculations are made of the heat flow from an initially cold earth with radioactivity distributed uniformly through a surface shell, with account taken of radioactive decay. It is found that the heat flow exceeds the heat produced by about 10 per cent if the abundances of radioactive elements are the same as in chondrites and the radioactive shell is less than about 300 km thick. The heat flow calculated in this way exceeds the observed value, but neither figure is considered known accurately enough to warrant rejection of the chondrite model of the earth.