HISTORY OF THE OCEANS

Earth Formed about 4.5 billion years ago The sea floor is locked in a perpetual cycle of birth and destruction that shapes the ocean and controls much of the geology and geological history of the continent

Geological Processes These processes that occur beneath the waters of the sea affect marine life and dry land. The processes that mold ocean basins occur slowly over tens and hundreds of millions of years Solid rocks flow like liquid, entire continents move across the face of the earth and mountains grow from flat plains

Geology Very important to marine biology Habitats are directly shaped by geology. The form of coastlines The depth of water The bottom surface – muddy, sandy, rocky The geologic history of marine life is also called Palentology.

OCEANS

Earth – Water Planet Oceans cover 71% of the Earth’s Surface. 2/3rds of the earth’s land area is found in the Northern Hemisphere which is only 61% ocean. About 80% of the Southern Hemisphere is ocean. Oceans play a crucial role in regulating our climate and atmosphere. Without water, life would be impossible.

The Ocean Traditionally classified into 4 large basins. Pacific – deepest and largest, almost as large as all others combined. Atlantic – little larger than Indian Indian – similar average depth to Atlantic Arctic – smallest and shallowest

The oceans cover 70.8 percent of planet Earth. By far the largest of the four oceans, the Pacific Ocean covers nearly one-third of the globe.

All the continents could be placed into the Pacific Ocean, and there would still be room left over. Average depth is 13,000 feet.

The hourglass shaped Atlantic Ocean covers approximately 20 percent of the Earth's surface and is the second largest of the 4 oceans. It extends from the North Pole southward for 10,000 miles to the Antarctic continent.

Average depth of the Atlantic Ocean is 12,000 feet. The greatest depth is 28,374 feet, the Puerto Rico Trench.

The Indian Ocean stretches southward from India to Antarctica. It is triangular and bordered by Africa, Asia, Antarctica, and, Australia.

The average depth of the Indian Ocean is about 12,750 feet. The deepest part is 24,440 feet in the Java Trench. The Indian Ocean, like the Atlantic Ocean is divided by a mid- ocean ridge that separates the basin into nearly equal portions.

Centered approximately on the North Pole, the ARCTIC Ocean is the smallest of the world's oceans.

ARCTIC OCEAN Maximum depth is 18,050 feet. The Arctic Ocean is divided into two nearly equal basins: The Eurasia basin & the Amerasia basin.

ARCTIC OCEAN The Arctic Ocean is surrounded by landmasses of Eurasia, North America, and Greenland, and is unlike the other three oceans because of the perennial ice cover.

Seas Connected or marginal to the ocean basins are various shallow seas: Mediterranean Sea Gulf of Mexico South China Sea

Oceanic Crustal Rocks Make up the sea floor Consists of minerals called basalt and have a dark color Denser than continental crust thus lies below sea level and is covered by water Only 200 million years old; continental crust can be as old as 3.8 billion years

Mid-Oceanic Ridge System 40,000 mile continuous chain of volcanic submarine mountains and valleys Encircle the globe like the seams of a baseball Largest geological feature on the planet At regular intervals the ridge is displaced to one side or the other by cracks in the earth’s crust called transform faults.

The Mid-Atlantic Ridge divides the sea floor nearly through the center and stretches from the polar regions of the North to Antarctica in the South.

The Mid Atlantic Ridge was created by the splitting apart of the super continent of Pangaea 190 million years ago.

Mid-Oceanic Ridge System Occasionally the submarine mountains of the ridge rise so high they break the surface to form islands such as: Iceland and the Azores Mid-Atlantic Ridge- runs right down middle of Atlantic Ocean East Pacific Rise – main section in the eastern Pacific Deep trenches are also common in the Pacific – deep depression in the sea floor

Earthquakes are clustered at the ridges Volcanos are especially common near trenches Rocks farther from the ridge crest are older

Plate Tectonics Earth’s surface is broken up into a number of plates. These plates, composed of crust and mantle make up the lithosphere. Plates are about 100km thick As new lithosphere is created, old lithosphere is destroyed elsewhere

Lithosphere is destroyed at the trenches. A trench is formed when two plates collide and one plate dips below the other and slides back down the mantle. Downward movement is called subduction. Subduction produces earthquakes and volcanoes, also underwater.

Earth’s Surface Continents have been carried long distances by the moving sea floor. Ocean basins have changed in size and shape. New oceans have been born. The continents were once united in a single supercontinent called Pangaea that began to break up about 180 million years ago.

Seawater Solids dissolved in seawater come from two main sources Some are produced by the chemical weathering of rocks on land and are carried to sea by rivers. Other materials come from the earth’s interior. Most of these are release into the ocean at hydrothermal vents.

Seawater

SEAWATER Only 6 ions compose 98% of solids in seawater Sodium and chloride account for about 85% of the solids, why it tastes like table salt. Salinity of the water strongly affects the organisms that live in it. Most marine organisms will die in freshwater. Even slight changes in salinity will harm some organisms.