Over vast periods of time, our primitive ocean formed. Water remained a gas until the Earth cooled below 212 degrees Fahrenheit . At this time, about 3.8 billion years ago, the water condensed into rain which filled the basins that we now know as our world ocean. 1521: Ferdinand Magellan tried to measure the depth of the Pacific Ocean with a weighted line, but did not find the bottom. 1818: The British researcher Sir John Ross was the first to find that the deep sea is inhabited by life when catching jellyfish and worms in about 2,000 m (6,562 ft) depth with a special device.
During planetary formation Earth possibly had magma oceans. Subsequently outgassing, volcanic activity and meteorite impacts, according to current theories, produced an early atmosphere of carbon dioxide, nitrogen and water vapor. The gases and with them the atmosphere are thought to have accumulated over millions of years and after Earth's surface had significantly cooled the water vapor over time would have condensed, forming Earth's first oceans. The early oceans might have been significantly hotter than today and appeared green due to high iron content.
Geological evidence helps constrain the time frame for liquid water existing on Earth. A sample of pillow basalt (a type of rock formed during an underwater eruption) was recovered from the Isua Greenstone Belt and provides evidence that water existed on Earth 3.8 billion years ago. In the Nuvvuagittuq Greenstone Belt, Quebec, Canada, rocks dated at 3.8 billion years old by one study and 4.28 billion years old by another show evidence of the presence of water at these ages. If oceans existed earlier than this, any geological evidence either has yet to be discovered or has since been destroyed by geological processes like crustal recycling. However, more recently, in August 2020, researchers reported that sufficient water to fill the oceans may have always been on the Earth since the beginning of the planet's formation. In this model, atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Ga, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.
Since its formation the ocean has taken many conditions and shapes with many past ocean divisions and potentially at times covering the whole globe.
The Seven Seas include the Arctic, North Atlantic, South Atlantic, North Pacific, South Pacific, Indian, and Southern oceans.