Significance of radioactivity in geophysics ‐ Thermal history of the Earth

Abstract

It appears that the effects on the Earth's thermal history of the exponential decay of the sources of atomic (radioactive) heat within the Earth are such that the upper crust of the Earth was heating in its early history and that subsequent cooling has been more nearly linear than has been supposed. In the deeper parts of the crust and below, the thermal history has been complex with simultaneous heating at one depth and cooling at another depth. Temperatures in the past beneath a Pacific‐type ocean have not varied in the same manner.Recent determinations of the radioactivity of ultrabasic rocks and iron meteorites are such that a monomineralic olivine mantle and an iron core will have remained essentially at the initial temperatures.The Earth, now presumably differentiated, may have had an earlier existence as an undifferentiated body formed by the coalescence of particles. Its rebirth as a molten, differentiated, and later frozen body is possible if the total radioactive content of the Earth was previously distributed uniformly and if its dust‐cloud origin dates back about seven billion years. A parental planet from which might have come the asteroids and meteorites may have disrupted because of stresses accumulated by internal heating.