The Oceans

Over two-thirds of the Earth’s surface is covered by oceans. The five major oceans, in order from largest to smallest, are: Pacific, Atlantic, Indian, Southern, and Arctic Oceans have been on earth for more than 3 billion years. Over two-thirds of the Earth’s surface is covered by oceans. The five major oceans, in order from largest to smallest, are: Pacific, Atlantic, Indian, Southern, and Arctic Oceans have been on earth for more than 3 billion years.

Origin of Ocean Water The water in the oceans came from water vapour released by volcanoes, and comets (“dirty snowballs” brought water from space) As the water vapour cooled, it condensed and fell to earth as precipitation, then ran downhill to collect in the lowest parts of Earth’s surface, the ocean basins. It took hundreds of millions of years for the oceans to fill up to their present levels Origin of Ocean Water The water in the oceans came from water vapour released by volcanoes, and comets (“dirty snowballs” brought water from space) As the water vapour cooled, it condensed and fell to earth as precipitation, then ran downhill to collect in the lowest parts of Earth’s surface, the ocean basins. It took hundreds of millions of years for the oceans to fill up to their present levels

Features of the Ocean Floor

the ocean floor has features that are a lot like features on land, such as mountains, steep valleys, and vast flat plains.

Submarine mountain Submarine canyon

The ocean floor has two parts: 1.Ocean basin, which is the largest part in the middle 2.Continental margins, which are the outside edges The ocean floor has two parts: 1.Ocean basin, which is the largest part in the middle 2.Continental margins, which are the outside edges

Earth’s crust shapes ocean basins The greatest influence in shaping the ocean floor is the movement of the Earth’s crust (the outermost layer of the Earth). The entire surface of the Earth is made up of large sections of rock called tectonic plates. These rock plates float over a layer of Earth called the mantle, that is made up of molten (melted) rock called magma. Earth’s crust shapes ocean basins The greatest influence in shaping the ocean floor is the movement of the Earth’s crust (the outermost layer of the Earth). The entire surface of the Earth is made up of large sections of rock called tectonic plates. These rock plates float over a layer of Earth called the mantle, that is made up of molten (melted) rock called magma.

Mantle made of magma Tectonic plates

Heat energy deep in the Earth heats up the magma. As the magma heats up, it becomes less dense and rises to the surface of the earth, where it cools and turns into rock. As more magma continues to rise to the surface, the new rock pushes the tectonic plates apart. Heat energy deep in the Earth heats up the magma. As the magma heats up, it becomes less dense and rises to the surface of the earth, where it cools and turns into rock. As more magma continues to rise to the surface, the new rock pushes the tectonic plates apart.

There are two types of tectonic plates: Oceanic plates lie under oceans and are thinner and denser Continental plates lie under continents and are thicker and more buoyant There are two types of tectonic plates: Oceanic plates lie under oceans and are thinner and denser Continental plates lie under continents and are thicker and more buoyant

When two oceanic tectonic plates are pushed apart, the magma rising up from inside the earth forms an undersea mountain range, called a mid-ocean ridge Mid-ocean ridge Magma

As the tectonic plates move apart, the ocean floors grows wider At the other side of the tectonic plate, it is colliding with another plate. When an oceanic plate meets a continental plate, the denser oceanic plate slides underneath the less dense continental plate. As the tectonic plates move apart, the ocean floors grows wider At the other side of the tectonic plate, it is colliding with another plate. When an oceanic plate meets a continental plate, the denser oceanic plate slides underneath the less dense continental plate.

Where one plate slides under another, an ocean trench is formed near the edge of the continent.

Between the mid-ocean ridge and the trench is a wide flat area called an abyssal plain. Underwater mountains in the abyssal plain, formed from old inactive volcanoes, are called seamounts. Between the mid-ocean ridge and the trench is a wide flat area called an abyssal plain. Underwater mountains in the abyssal plain, formed from old inactive volcanoes, are called seamounts.

Continental margins are the regions of the ocean floor which lie along the edges of continents. These are made up of several parts: Continental shelf = a flat area (like a shelf) that extends from the shoreline to the ocean basin Continental margins are the regions of the ocean floor which lie along the edges of continents. These are made up of several parts: Continental shelf = a flat area (like a shelf) that extends from the shoreline to the ocean basin

Continental slope = a steep area that drops off rapidly to the ocean basin from the edge of the continental shelf Continental rise = at the base of the slope a more gentle slope formed of sediments from turbidity currents (underwater landslides) Continental slope = a steep area that drops off rapidly to the ocean basin from the edge of the continental shelf Continental rise = at the base of the slope a more gentle slope formed of sediments from turbidity currents (underwater landslides)

Submarine canyons = deep gullies formed by turbidity currents and by large rivers when they meet the ocean.

shoreline shelf slope rise Turbidity current seamount canyon Abyssal plain