Water Cycle - Oceans (5)

  • Exploring what lies on the ocean floor.
  • Discovering the importance of the oceans.
  • dredge 
  • echo sounding

Students look at dredge samples.



The bottom of the oceans is rich in deposits of sediments with some economic importance.  In some areas of the ocean they mine for lime, sand, and gravel  that are used in the concrete industry.  In other areas the oil industry may find oil reserves.  

However, we must look at the ocean bottom differently than if we are looking on land.  The water distorts our view and we must use indirect methods to look at the floor of the oceans.  There are many different techniques used in underground or undersea exploration and prospecting.  They can take indirect pictures of the seafloor by using seismic techniques.  This allows energy waves to penetrate an area and then a geologist will interpret the pictures that are derived from this method.  

A core  sample is a roughly cylindrical piece of subsurface material removed by a special drill and brought to the surface for examination.  Coring devices helps to recover samples of fine-grained deposits on the seafloor in such a way as to preserve the depositional history through time. By studying the mineral grains, microfossils, and water in the pore spaces, scientists have been able to infer the past oceanic events.

  1. This lab looks at the features of the ocean floor. Remind the students that it is very difficult to know what is down there. First students will look at echo soundings and seismic records of the bottom of the oceans. These help scientists look at the surface of the ocean and to look at the structure of the rocks. 
    Echo sounding devices use an instrument similar to that used when a doctor looks at a baby in a mother's womb by giving an impression of the surface of the ocean floor (topography). The breaks in each of the pictures are just a consequence of the system. Echo soundings are taken when an instrument from the ship makes a noise which is then recorded on the ship when the sound "bounces" back from the bottom.

    The picture is a seismic profile. This gives the scientist more detail of can be found on the bottom and can be read by geologists to determine what kind of rocks are down there. A seismic profile uses different types of "waves" to look at the rocks below the surface.

  3. Students should look at different components of the ocean bottom. Students will determine that some of the materials that you find underneath the oceans are similar to what we see on land. Some of the samples are not really from the location because of cost factor. However the manganese nodules and pillow basalt displays are the real substance. The material was obtained from the U.S. Geological Survey.
    Marine geologists determine what can be found on the ocean floor by taking dredge samples. A dredge sample is obtained by "scraping" up parts of the ocean floor using a crane-like device. This is not very scientifically correct or standard, but it helps. There are many other ways to look at the bottom of the oceans. The samples used in this lab are dredge samples from various parts of the ocean.   The main objective is for students to recognize the oceans contain many things.
  4. The samples in your module include:

Bahamas. Whole shells and broken up shells, mixed together with some small rock pieces; light brown in color, some plant matter. Used as sand in concrete.
Manganese "crusts" found west of Hawaii in the Pacific Ocean. The sample is  large to small (brown-brown, yellow) rock pieces; some pieces look like coal. Used for manganese, cobalt, and nickel.
Monterey Canyon
, off of Moss Landing; in  California is a canyon deeper than the Grand Canyon  The sample is  medium to large grains of sand, black minerals and pink minerals. The Monterey Canyon is so deep that it is not mined, but the sand could be used in the concrete business.

East Pacific Ocean, near Hawaii  is where these pillow basalts were found.  Your specimen is only pieces of large boulder basalts that form when magma oozes up from the ocean floor and cools quickly.  There is a shiny outside surface which is obsidian and had first contact with the water and cooled first.  The basalt would have cooled later. 

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