Thermal History of the Earth with Consideration of the Formation of Its Core

Abstract

Various possible ways of core formation are tested from the thermal history of the Earth. Calculation shows that the conversion of gravitational to thermal energy from a uniform to the present differentiated Earth is 1.68×1038 ergs. It is concluded that the release of the gravitational energy on core formation dominates the thermal state of the Earth.Earth models in which the core has been growing slowly since 4500 My ago or 3000 My ago fail to meet the requirement of a solid mantle. In these models the present surface heat flows are in excess of the observed heat flow.Earth models in which the core was substantially complete at 4500 My ago or 3000 My ago within a short period less than 100 My give the observed heat flow.The gravitational energies released in reconstruction of the terrestrial planets are also calculated. Calculation gives the gravitational energies of 1.02×1038 ergs, 1.10×1036 ergs, and 1.34×1036 ergs for Venus, Mars, and Mercury respectively. The results show that the energies released by the formation of iron cores of the Earth and Venus play an important role for the internal heating of these planets.