The Ocean

More than 70 percent of the earth’s surface is covered with water, and 97 percent of this water forms an ocean that wraps around the planet. The ocean began forming billions of years ago when the earth started to cool from its original molten state. Water vapor, which had escaped from within the planet during volcanic eruptions, condensed and fell as rain. Scientists believe that, over vast stretches of time, this rain filled the depressions in the planet’s surface.

During the course of the earth’s history the land surrounded by this ocean has been configured in different ways. At one time most of the landmass had drifted together to form on super-continent and two or three large islands. Then, about 200 million years ago, this landmass began to break up as the plates that form the earth’s crust started to shift. This shifting of plates and land, which continues today, has resulted in the present configuration of continents.

Despite the new distribution of land, however, the ocean has remained one body of water. Although we typically refer to the Atlantic, Pacific, Indian, and Arctic oceans as separate bodies of water, a glance at any globe clearly shows that all of the oceans are connected.

Why is the ocean salty?

Weathering breaks rocks down into smaller and smaller particles. Rain washes many of these particles into rivers and streams, which dissolve the soluble parts and carry them to the ocean. The dissolved mineral components that contribute significantly to the ocean’s salinity– the amount of salts in the water– are chloride, sodium, magnesium, calcium, and potassium. This salinity, which averages 3.45 percent by weight, can be viewed as consisting mainly of the compound sodium chloride (table salt). A salinity of 3.45 percent means that 100 grams of ocean water would contain 3.45 grams of salt and 96.55 grams of fresh water.

Undersea volcanoes and springs release minerals into the water. However, these processes, which tend to increase the salinity, are continually being counteracted by other processes, both chemical (precipitation) and biological (coral and shell formation), that cause minerals to leave the ocean water or that add water to the ocean. For example, though water evaporation contributes to the ocean’s salinity by removing fresh water from the surface, most of the fresh water that is removed falls back into the ocean. Most earth scientists believe that this counteraction of processes has been responsible for the relatively constant salinity of the ocean since earliest times, despite the continual addition of minerals from the land.

Most deep-water waves are produced when the energy of the wind is transferred to the water through friction. In such waves energy moves forward through the wave, but the water particles themselves simply move in a circular orbit, with little forward motion. The waves that crash onto a beach are shallow-water waves. In this type of wave, the top of the wave falls forward as the lower part of the wave is slowed by the sea bottom.

Tides are actually very long waves caused by the gravitational pull of the moon and, to a far lesser extent, the sun. High tide occurs as the moon’s gravity pulls most strongly on the ocean waters facing the moon, causing the water to pile up in a bulge. At the same time, the moon’s gravity pulls a little less strongly on the earth itself and even less strongly on the oceans on the opposite side of the earth. The result is simultaneous high tide on the opposite side of the earth. This action explains why at any given time, high tide is occurring at two opposite points in the ocean. It also explains why high tides occurs twice a day, about 12 hours apart.

Ocean currents are caused by the uneven heating of waters by the sun and by the force of steadily blowing winds. In both the Northern and Southern hemispheres, steady winds called trade winds blow diagonally toward the equator from the east. These winds move the sea westward in huge currents. As a result, because the earth spins eastward on its axis, the “Coriolis effect” creates circular ocean currents that move clockwise in the Northern Hemisphere and counterclockwise in the Southern. The Coriolis effect can be seen every day in the vortex motion of tap water as it goes down the drain.


“Black Smokers” are named for the soot-like appearance of the ejected material billowing out of the “chimneys”. This substance is super-heated water with very high concentrations of dissolved minerals. As the super-heated water meets the very cold ocean-bottom water, the dissolved minerals precipitate out and settle onto the rock around them. This causes the chimneys to grow in height over time.


Giant Kelp likes cool water. It won’t grow more than 100 feet below the surface of the water because it needs light for photosynthesis.


The fish below is called a Whitemargin Stargazer. This fish is a wonderful example of how life can evolve to mimic its surroundings. It hides in the sand and waits for prey to swim by. Those aren’t teeth that you see around its mouth; the bumps keep sand out.


Green sea turtles are also very well suited to their environment. Nine minutes can pass between a sea turtle’s heartbeats, meaning it can stay underwater for hours at a time!


Dolphins are mammals that communicate using clicks, squeaks, and whistles. They have excellent hearing. nIf a dolphin is hurt, other dolphins will stay near it and help it get to the surface so that it can breathe. A dolphin does not breathe through its nose, it breathes through a blowhole.

Plankton may be the most important life form in the ocean. Many, many animals eat this plankton that exists in abundance floating in the waters of the sea.


purse seine nets