According to the scientific hypothesis known as the "Hydrothermal Vent Theory", the formation of oceans is believed to have occurred during the early stages of Earth's history. Here's an overview of how oceans formed according to this theory:

1. Formation of Earth: The Earth formed approximately 4.5 billion years ago from the accretion of cosmic dust, gas, and debris left over from the formation of the sun. The early Earth was extremely hot and in a molten state.

2. Outgassing and Water Vapor: As the Earth cooled, its interior began to solidify, forming the Earth's crust. The process of outgassing released gases and water vapor from the interior of the Earth into the atmosphere.

3. Water Vapor Condensation: The water vapor in the atmosphere condensed to form clouds, and eventually, rain began to fall. The heavy rainfall filled the depressions and lowlands on the Earth's surface, forming bodies of water.

4. Hydrothermal Vents: The heat from the Earth's interior caused volcanic activity and the formation of hydrothermal vents on the ocean floor. These vents spewed out hot water rich in dissolved minerals, which mixed with the seawater and contributed to the chemical composition of the oceans.

5. Chemical Reactions: The interaction between the Earth's crust and the hot hydrothermal fluids led to various chemical reactions. These reactions produced important compounds and minerals, such as salts and carbonates, that contributed to the salinity and composition of the oceans.

6. Accumulation and Growth: Over time, the water from rainfall, as well as the continuous release of water from hydrothermal vents, accumulated and filled the depressions on the Earth's surface. As more water was added, the oceans grew larger and covered a significant portion of the Earth's surface.

7. Plate Tectonics: The movement of tectonic plates over time played a role in shaping the oceans. The collision and separation of tectonic plates created oceanic basins, mountain ranges, and continents, further defining the boundaries of the oceans and their interactions with landmasses.

It's important to note that the formation of oceans was a gradual process that took place over millions of years. The Hydrothermal Vent Theory is widely supported by scientific evidence, but ongoing research and new discoveries continue to contribute to our understanding of how oceans came to exist on Earth.