<p>The redox state of the atmosphere and hydrosphere was essential to the origin of life on Earth and its long-term habitability. In this Review, we explore the formation and redox evolution of the Earth’s early atmosphere and hydrosphere, combining evidence from meteorites, the ancient rock record and numerical models. The initial atmosphere was formed by primordial volatile accretion, primary magma-ocean outgassing and secondary volatile outgassing after magma-ocean crystallization during the Hadean aeon (4.567–4.0 Ga). An initial hydrosphere could have developed as early as 4.4 Ga, but probably underwent episodic vaporization during late accretion. The earliest robust evidence of subaqueous environments is dated at about 3.7 Ga. The mantle reached its modern-day redox state between 4.4 Ga and 2.7 Ga. Free O₂ in the hydrosphere appears at 3.0 Ga, whereas the initial rise of atmospheric O₂ (the ‘Great Oxidation Event’) occurred later, at 2.5–2.3 Ga. This delay in the surface oxidation was probably caused by a synergy of geodynamic, magmatic and (bio)geochemical mechanisms modulating oxygen sources and sinks. These processes in turn shifted the dynamics of other volatile element cycles important to the evolution of life, such as nitrogen, carbon and hydrogen. Future work should prioritize determining further quantitative constraints on Earth’s oxygen sources and sinks through time to understand the habitability of early Earth.</p>