|Physical Science||Structure of Earth 7I2.00||Process of Science||Questioning 1.2 a|
Sponsored by the National Science Foundation
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:
TN COMPONENT OF SCIENCE: Process of Science
BENCHMARK: Shared experiences may help to develop an inquisitive mind.
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.
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.)
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.
Seventh Grade Science Home Page