Abstract
The processes and chronology of the early growth of objects in the inner solar system can be inferred from the chemical and mineralogical information derived from meteorites and Earth materials. Improved analytical precision in selected radioactive isotope decay systems provides tight time constraints on flash melting pulses in the solar nebula (time zero) and magma ocean crystallization in planetesimals and planets. The energy for the very early whole-scale melting and metal separation (core segregation) of small bodies (10-500 km size) was mostly radioactive heat from very short-lived isotopes like Al-26 and Fe-60. Subsequently, copious amounts of gravitational and collisional energy were released when the runaway growth of planetary embryos reached the giant collision stage. The Earth’s moon was formed in a giant collision with a Mars-sized protoplanet (Theia), adding the last 10 % of Earth’s mass and creating the nearly core-free Moon. This collision and the associated lunar magma ocean crystallization occurred 35-45 million years after time zero. The age and mass fraction of planetary cores provide valuable insight in terrestrial planet growth.