Why do oceans cover about 71 percent of Earth’s surface?

The presence of oceans covering approximately 71 percent of Earth’s surface is the result of the planet's early geologic history and the condensation of water vapor.

During the early stages of Earth's formation, volcanic degassing released significant amounts of water vapor and other gases from the planet's interior into the atmosphere. As the surface of the planet cooled to below 100 °C (212 °F), this water vapor condensed into liquid form. This liquid water accumulated in the depressions of Earth's surface, forming the nascent oceans.1234

While the specific mechanisms of how water first arrived on Earth—whether through internal chemical reactions or delivery by comets and meteorites—remain a subject of scientific debate, it is widely accepted that the hydrosphere reached its present volume early in the planet's history. Since that time, there have been no significant additions to the total volume of water on Earth; rather, changes in the distribution of land and sea have been driven by plate tectonics and shifts in sea level caused by the growth and melting of ice sheets.54