This chapter traces the emergence of life on Earth from the violent Hadean Era through the rise of mitochondria‑bearing eukaryotic “supercells,” highlighting how early planetary conditions shaped biology’s fundamental architecture. It follows the progression from prebiotic chemistry and the RNA World—supported by both asteroid‑delivered organics and Earth’s own geochemical processes—to the appearance of protocells, prokaryotes, photosynthesis, and the Great Oxidation. It then examines the pivotal symbiotic events that produced mitochondria and chloroplasts, the massive evolutionary relocation of mitochondrial genes to the nucleus, and the vulnerability of the remaining mtDNA to damage. The chapter concludes by framing mitochondrial decline as the long‑term energetic cost of the ancient endosymbiotic "Faustian Bargain" that enabled complex life, linking early Earth history directly to the biology of aging today.