Clues on the importance of comets in the origin and evolution of the atmospheres of Titan and Earth

► We explore the chemical and isotopic affinity of Earth and Titan atmospheres. ► A common origin in water-rich bodies fallen during the late bombardment is suggested. ► The evolution of both planetary bodies is explored using equilibrium thermodynamics. ► Late accretion was crucial to enrich Earth's organic content at the time life appeared. ► Impacts products promoted a reducing atmosphere and increased the organic complexity.