Earth is the only planet known to have an ocean (or any large amounts of open liquid water). Approximately 72% of the planet’s surface (~3.6×108 km2) is covered by saline water that is customarily divided into several principal oceans and smaller seas, with the ocean covering approximately 71% of the Earth’s surface.[6] In terms of the hydrosphere of the Earth, the ocean contains 97% of the Earth’s water. Oceanographers have stated that out of 97%, only 5% of the ocean as a whole on Earth has been explored.[6] Because it is the principal component of Earth’s hydrosphere, the world ocean is integral to all known life, forms part of thecarbon cycle, and influences climate and weather patterns. The total volume is approximately 1.3 billion cubic kilometres (310 million cu mi)[7] with an average depth of 3,682 metres (12,080 ft).[8] It is the habitat of 230,000 known species, although much of the ocean’s depths remain unexplored and it is estimated that over two million marine species exist.[9] The origin of Earth’s oceans is still unknown, but oceans are believed to have formed in the Hadean period and may have been the impetus for the emergence of life.
| Rank | Ocean | Notes |
|---|---|---|
| 1 | Pacific Ocean | Separates Asia and Oceania from the Americas[14] |
| 2 | Atlantic Ocean | Separates the Americas from Eurasia and Africa |
| 3 | Indian Ocean | Washes upon southern Asia and separates Africa and Australia[14][15][16] |
| 4 | Southern Ocean | Sometimes considered an extension of the Pacific, Atlantic and Indian Oceans,[11][17] which encircles Antarctica |
| 5 | Arctic Ocean | Sometimes considered a sea of the Atlantic, which covers much of the Arctic and washes upon northern North America and Eurasia |
