Earth's primordial conditions at the beginning of geologic history (Hadean Eon) witnessed several fundamental processes, including cooling and crystallisation of a magma ocean, the Moon-formation impact event, the faint young sun paradox, the late heavy bombardment (LHB), origin of pre-biotic molecules and probably life itself, as well as the transition from reduced to oxidised outer Earth's layers. This book assesses and analyses the latest information about the primitive Earth's environments in the Hadean to Archean transition, including the faint young sun paradox, possible reservoirs of pre-biotic molecules, early carbon cycle and the most favourable niches for the emergence of life.