Over millions of years, ocean basins open and close, continents move and change shape, and mountains are pushed up and eroded away. Such dynamic processes continually reshape the surface of the Earth. The movement of rigid plates on the Earth’s surface, known as plate tectonics, is the cause of these changes.

Amazon Basin

Historically, there are four named oceans: the Atlantic, Pacific, Indian, and Arctic. However, most countries – including the United States – now recognize the Southern (Antarctic) as the fifth ocean. The Pacific, Atlantic, and Indian are the most commonly known.

Without this water, Earth would not have the diversity of life forms, the continents we live on (it takes water to create most continental rocks), or the atmosphere that protects us. If Earth’s surface were entirely smooth, with no mountains or basins, water would cover the entire planet.

Together they contain the overwhelming majority of all water on the planet and have an average depth of almost 4 km (about 2.5 miles). A number of major features of the basins depart from this average—for example, the mountainous ocean ridges, deep-sea trenches, and jagged, linear fracture zones.

Ocean ridges, deep-sea trenches, abyssal hills, fracture zones, seamounts, and guyots are some of the major features of an ocean basin.

The five ocean basins from largest to smallest are: the Pacific, Atlantic, Indian, Southern, and Arctic.

Features of the Ocean

• Intertidal or Littoral – located from high tide to low tide areas.
• Continental shelf – located from low tide to the edge of the shelf.
• Continental slope – where the ocean bottom slopes steeply to the ocean floor.
• Abyssal plane – the ‘bottom’ of the ocean where it is relatively flat.

Underwater landforms

• Continental shelf. Starting from land, a trip across an ocean basin along the seafloor would begin with crossing the continental shelf.
• Abyssal plains. Continuing your journey across the ocean basin, you would descend the steep continental slope to the abyssal plain.
• Mid-ocean ridge.
• Ocean trenches.

Features of the ocean include the continental shelf, slope, and rise. The ocean floor is called the abyssal plain. Below the ocean floor, there are a few small deeper areas called ocean trenches. Features rising up from the ocean floor include seamounts, volcanic islands and the mid-oceanic ridges and rises.