  The number of active volcanoes and its latitudinal extent is likely to be
related to the magnitude of internal heat in rocky planets. A critical value of
internal heat may require in these planets to sustain volcanic activity and the
decline of volcanic activity since their formation of these planets is inferred
to be governed by radioactive decay laws. We find that major volcanic activity
in Mars, Moon, Mercury and Venus has ceased when their respective surface heat
flux values are within ten percentage of the current surface heat flux value of
Earth. The reduction in spatial extent of recent volcanic activity in Venus
compared to the geological past is inferred to be part of significant reduction
in volcanic activity in this twin planet of Earth. We suggest that the volcanic
activity in Earth is also declining significantly since the period of mass
extinction of dinosaurs 65 million years ago. It may cease completely within a
time span between 19 to 65 million years from now with possible implications in
Earth's interior, climate and biosphere.
