OLP 1: The Earth has one big ocean with many features

Representative Image

The ocean is the defining physical feature on our planet Earth—covering approximately 70 percent of the planet’s surface. Throughout the ocean there is one interconnected circulation system.



Image caption

Fig. 1. OLP 1. The ocean on Earth from space.

Image copyright and source

Image courtesy of National Aeronautics and Space Administration (NASA) Goddard Space Flight Center


The ocean is the defining physical feature on our planet Earth—covering approximately 70 percent of the planet’s surface. There is one ocean with many ocean basins: North Pacific, South Pacific, North Atlantic, South Atlantic, Indian, Southern, and Arctic.


Ocean basins are composed of the seafloor and all of its geological features (such as islands, trenches, mid-ocean ridges, and rift valleys) and vary in size, shape, and features due to the movement of Earth’s crust (lithosphere). Earth’s highest peaks, deepest valleys, and flattest plains are all in the ocean.


Sea level is the average height of the ocean relative to the land, taking into account the differences caused by tides. Sea level changes as plate tectonics cause the volume of ocean basins and the height of the land to change. It changes as ice caps on land melt or grow. It also changes as seawater expands and contracts when ocean water warms and cools.


Most of Earth’s water (97 percent) is in the ocean. Seawater has unique properties. It is salty, its freezing point is slightly lower than that of fresh water, its density is slightly higher, its electrical conductivity is much higher, and it is slightly basic. Balance of pH is vital for the health of marine ecosystems and important in controlling the rate at which the ocean will absorb and buffer changes in atmospheric carbon dioxide.


The ocean is an integral part of the water cycle and is connected to all of Earth’s water reservoirs via evaporation and precipitation processes.


The ocean is connected to major lakes, watersheds, and waterways because all major watersheds on Earth drain to the ocean. Rivers and streams transport nutrients, salts, sediments, and pollutants from watersheds to coastal estuaries and to the ocean.


Although the ocean is large, it is finite, and its resources are limited.

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Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawai?i, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.