GRADE: Seventh

CONTENT STANDARD: Earth and Space Science

CONTENT TOPIC: Structure of Earth

CONCEPT: The importance of the ocean is evident in its life forms, physical features and resources.

CONTENT OBJECTIVE: 7I6.00 To understand the physical features of the ocean

INSTRUCTIONAL OBJECTIVES: The learner will:

2.01 be able to construct a model ocean basin complete with appropriate terminology
2.02 recognize that the morphology of the ocean basins is varied and extensive
2.03 describe mid-ocean ridges and how they are formed
2.04 relate vertical movement in the crust of the earth with Eniwetok Atoll.

I. Origin of the oceans
II. Morphology of ocean basins
III. The ocean's landscape
IV. Sea-floor spreading and plate tectonics
V. Oceanic currents

TN COMPONENT OF SCIENCE: Process of Science

TN GOAL:

To enable students to demonstrate the processes of science by posing questions and investigating phenomena through language, methods and instruments of science.

1.2 QUESTIONING - The development of an inquisitive mind and the effective use of questioning techniques furthers the acquisition of information.

1.2a - Initial information and prior knowledge are used to ask questions.

BENCHMARK: Shared experiences may help to develop an inquisitive mind.

TIME REQUIRED:

3 days

chalk and chalkboard, aquarium, clay

Coral reef, Eniwetok Atoll, mid-ocean ridge, plate tectonics, rift valley, sea-floor spreading, terrestrial biomes, trenches, turbidity currents

This week we will be learning about some of the physical characteristics of the oceans - the largest ecosystems on earth. Most of the earth, some 70% is covered by vast interconnected expanses of water, the oceans and seas. These have been a primary route of exploration throughout the world since early times; they have served as vital routes of transportation, and as an important source of food for maritime civilizations.

The oceans were first formed as water condensed out of the atmosphere of the primeval earth and settled in the lowermost parts of the newly formed crust. According to current geological theory, all the land on earth - that portion of the earth's crust above sea level - formed a single "supercontinent" during the first three or four billion years of the earth's history. The continent was surrounded by a single ocean. Some 200 million years ago, this single land mass began breaking apart, ultimately to form the continents we know today. From this process of continental drift, the ocean floors have spread and original enlarged, and thus taken on their basic morphology. The Pacific Ocean of today is a remnant of the original, single ocean and the Atlantic Ocean fills a rift that was left when the Americas and Antarctica became separated from the African and Eurasian land masses. The Mediterranean Sea, now an arm of the Atlantic Ocean, has undergone episodes of dramatic change, having been at different times a desert and the floor of an inland sea.

The floor of the ocean is largely covered with unconsolidated sediment, consisting of particles which have settled down from higher regions. The sediments reach thicknesses of thousands of meters, and the great pressure exerted by the weight of such masses of material consolidates the bottom-most portion into sedimentary rock. All of the surface material of the earth tends to move downslope under the influence of gravity. These downslope movements shape the earth's surface. Erosion of rock makes nutrients available. These rocks may be classified on the basis of the materials from which they were originally formed.

Most of the ocean floor is fairly level or gently undulating. The ocean floor has many features similar to those of terrestrial biomes. Less than 20% of the sea floor has been sounded; however, oceanographers know that the oceans have an average depth of about four kilometers. In addition, they know that features on the floor of the ocean are much larger than similar features on land. Deep ocean trenches are over 10,000 meters deep. The greatest oceanic depth so far recorded, 11,515 m, is in the Mindanao Trench, east of the Philippine Islands. The Grand Canyon is 1,700 meters deep. The mid-ocean ridge extends from Iceland through the entire length of the Atlantic Ocean. It continues into the Indian Ocean and then into the Pacific. The mid-ocean ridge consists of mountains beneath the sea. Over much of its length, the center of this ridge is split by a rift valley. Many earthquakes occur near the rift valley in the center of the ocean. The floor of the rift valley gives off heat more rapidly than do other parts of the sea floor. The greater heat flow and earthquake activity suggest that the mid-ocean ridge is active geologically. These ridges and zones of activity are thought to be the primary regions where new material rises from the earth's centers of sea-floor spreading (and consequently of continental movement). As the ocean floor is moved toward the continents, it is forced beneath the continental masses at some points, thus forming the trenches. Other major features of oceanic basins are continental shelves, submerged extensions of the continental masses, usually lying at depths of less than 200 m. The depths and widths of the continental shelves vary considerably. In the Atlantic, the continental shelf accounts for a significant part of the ocean's surface area, whereas in parts of the Pacific, the continental shelf is so narrow as to be nonexistent.

There are plains and hills on the ocean's floor. Deep-sea plains exist only where turbidity currents can reach the ocean floor to deposit sediments. Most deep-sea hills are only a few kilometers wide and a few hundred meters high. Seamounts are larger hills and peaks of the ocean floor that rise more than 1,000 meters above the general level of the sea floor.

Sea-floor features are formed when the sea floor spreads apart from the rift valleys in the mid-ocean ridge. They come together at the deep-sea trenches. There, one plate rides over the top of another. The bottom plate is dragged into the earth's mantle. Deep-sea trenches are formed.

Eniwetok Atoll is a classic example of movement in the earth's crust. The coral reefs of Eniwetok are 1400 meters high. Coral reefs form in warm, shallow water This proves that at one time the sea floor which supports this coral reef was in shallow water.

The volume of water in the ocean basins is estimated at 1.37 billion cubic kilometers, and most of this is in motion in the major ocean currents. The constant flow of oceanic waters affects conditions where organisms live, warming the eastern continental coasts and northern portions of west coasts of continents and cooling the other western portions of continents. Currents are of great importance in the ecology of islands and other terrestrial ecosystems, since currents transport water-resistant seeds to distant regions, and many plant and animal species have been dispersed widely by drifting on "rafts" of matted vegetation. Similar drifting determines the distribution of suspended forms of marine life. Oceanic currents also affect plant and animal life throughout the earth by distributing solar heat. Marine waters absorb tremendous amounts of heat in the equatorial regions; oceanic currents redistribute this heat, arming coastal regions and landmasses quite far poleward.

1. Have the class divide into groups of six and have each group make a model of the significant formations in the world's oceans. They can do this easily with materials from home. Putty can be utilized easily and cheaply. Allow them to use their imagination with this project. Provide ample pictures and illustrations of these major formations.)

2. Using an aquarium, clay, and water, reconstruct a model of an ocean basin. Fish and other small aquatic animals can be placed in the aquarium for visual purposes. Outside the tank, a terrestrial biome can be constructed to include a land mass of some type, mountains, rivers, and even a volcano. The students should be encouraged to express themselves fully in this activity.)

We have spent three days studying the earth's ocean basins. You have reconstructed the major formations of the ocean in the form of a topographical world map. Tell me some of the reasons scientists have some difficulties determining facts about the sea floor. (response) For those of you who find this type of research interesting, list any ideas you have which might aid in this work. (response) Who knows?, we may be in the same room with a future oceanographer.

coral reef - a rock built of organic remains

Eniwetok Atoll - coral reef found in the Marshall Islands which has been the subject of much ecological study

mid-ocean ridge - mountains beneath the sea

plate tectonics - theory concerning plate movement due to seismic activity

rift valley - valley formed along a rift fault or lateral fault; a fault being a break in the earth's crust along which movement has occurred

sea-floor spreading - movement of the sea-floor away from the mid-ocean ridge

terrestrial biomes - land masses

trenches - a very deep area of the ocean, associated with volcanic island arcs

turbidity currents - a current or flow caused by the movement downslope of water heavy because of its suspended material (muddy water)

This is the time this file has been accessed since 04/02/98.

The University of Tennessee at Martin is not responsible for the information or views expressed here.

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