The Epoch of Extreme Inundations (EEI) is a hypothetical epoch during which four landforms in the Pontic–Caspian steppe—marine lowlands (marine transgressions), river valleys (outburst floods), marine transgressions (thermocarst lakes) and slopes (solifluction flows)—were widely inundated. Catastrophic events during the epoch are theorized to have influenced prehistoric human life.