Scale of the Oceans
The oceans, which make up Earth’s largest habitat or biome, can be divided into 3 zones:
- inshore water
- continental margin
- open sea
The world has 5 major oceans: Pacific, Atlantic, Indian, Arctic and Southern, in descending order of size.
| Ocean | Area |
| Pacific | 155,557,000 sq km |
| Atlantic | 76,762,000 sq km |
| Indian | 68,556,000 sq km |
| Southern | 20,327,000 sq km
|
| Arctic | 14,056,000 sq km |
By far the largest of the oceans, the Pacific covers nearly one third of the globe. The Pacific Ocean is immense. All the continents could be placed into it, and there would still be room left over. However, the Pacific is probably the most violent of all oceans as it has typhoons in the equatorial regions, nearly 300 active volcanoes which vent steam and smoke on her borders, and tidal waves which are periodically unleashed.
Straits of Magellan
Smaller regions of the oceans are called seas, gulfs, straits and other names. Geologically, an ocean is an area of oceanic crust covered by water. Oceanic crust is the thin layer of solidified volcanic basalt that covers the Earth’s mantle where there are no continents.
While oceans may look featureless, below the surface is a dramatic landscape that is rarely seen of volcanoes, mountains, trenches and ridges that pour out lava where oceanic plates meet. Over half the seabed under the oceans has huge, flat plains called abyssal plains (the term refers to the large, deep parts of the ocean) and this is regarded as the true ocean floor. Abyssal plains are amongst the smoothest surfaces on the planet and have been compared to the flat prairie lands of mid America.
Mid Atlantic Ridge
All the large oceans have under-sea mountain ridges and a number are longer than the longest mountain ranges on Earth. The longest is the Mid-Atlantic Ridge that stretches from north of Iceland to Antarctica and was created by the splitting apart of the super continent of Pangaea 190 million years ago. At 11,300 km the Mid-Atlantic Ridge is 4 times longer than the Himalayas, Andes and Rockies combined.
Trenches are found adjacent and parallel to continents and island chains. Depths of the major trenches exceed 10,000m and are greater than the elevation of the world’s highest mountain, Mount Everest. The Marianas Trench in the Pacific Ocean at 10,911m deep, is the deepest point in any of the world’s oceans.