Nearly 3.8 billion years ago, temperatures on Earth cooled below 100 degrees Celsius for the first time, allowing water, which existed on the planet in gaseous form, to condense into rain and collect on the planet's surface, according to the American Museum of Natural History. This water collected in low-lying areas, eventually becoming a primitive ocean.
This early ocean was likely very shallow and covered the majority of the Earth's surface, as continents did not exist yet and would not for some time, according to the American Museum of Natural History.
A report by the BBC indicates that the most recent of all supercontinents to form on the planet, Pangea, formed about 270 million years ago and split into sections about 200 million years ago. Pangea was a landmass covering almost one-third of the planet's surface. Scientists refer to the surrounding ocean as Panthalassa.
Pangea began splitting down the middle, allowing the Atlantic Ocean to form between South America and Africa and between North America and Europe, according to an article from the Rutgers University Department of Geologic Sciences. Signs of that split are visible on the floor of the Atlantic Ocean. Additional fractures allowed smaller oceans, such as the Indian Ocean, to form. The Pacific Ocean represents much of what was originally known as Panthalassa.