back to index ofchapters1. How much of the Earth's surface is covered by the oceans?
Ans. 71 per cent.
2. Name the four major oceans. What percentage of the Earth's water isfound in each of the oceans?
Ans. Pacific 33 per cent, Atlantic 16 per cent, Indian 14 per cent andArctic 3 per cent.
3. Draw a diagram to compare the height of mountains to the depth ofocean trenches.
Ans. See Figure 93.3
4. Write a paragraph describing the formation of the Earth's oceans.
Ans.
· The most popular theories explaining the formation of the Earthabout four to five thousand million years ago, say it was formed as a hotplanet. The molten mass of the planet eventually cooled to form heightsand basins which became the continents and the oceans.
· Many geologists believe that volcanic activity gradually releasedwater vapour into the atmosphere as shown in Figure 93.1. This water wasoriginally chemically combined in the rocks and the chemical bonds werebroken by the heat, releasing the water into the atmosphere. This formeda mass of clouds around the earth many metres thick.
· After millions of years, the Earth lost its heat into space.As the Earth cooled, the water vapour condensed to form rain. The Earth'ssurface cooled even more, causing a hard layer or crust to be formed onthe outside. It must have rained for hundreds of thousands of years forthe oceans to gradually fill.
5. Oceanography is the study of the oceans. Name its four branches andsay what is studied in each branch.
Ans.
· Physical oceanography is the study of the oceans' buoyancy,temperature, the circulation of oceanic water and light penetration. Physicaloceanographers are very interested in the effects the depletion of ozonein the atmosphere has on the oceans as well as ocean currents discussedin Chapter 12.
· Geological oceanography is the study of the ocean floor, featuresof the oceans' depths and coastal features. Figure 92.1 shows a offshoreoil rig that relies on the data geological oceanographers relay to drillingengineers.
· Biological oceanography is the study of marine plants and animals.The students in Figure 92.2 have just hauled up a sample from the oceanfloor and will now identify what lives on the sea bed in their area.
· Chemical oceanography is the study of the chemical compositionof the oceans, salinity and the amount of dissolved gases in the oceans.The marine scientists in Figure .3 are about to launch a series of watercollection bottles which will collect water samples from a number of depths.
6. Draw a fully labelled diagram of the hydrological cycle.
Ans.
See Figure 94.1
7. Define these terms:
Ans.
a. precipitation - the deposition of moisture from the atmosphere ontothe earth by rain, snow or hail
b. condensation - the conversion of water vapour into liquid
c. transpiration - the loss of water from plants by evaporation
d. greenhouse effect - the buildup of carbon dioxide and other gasesin the atmosphere which prevents heat loss.
8. Why is the greenhouse effect so called? Which gases cause the greenhouseeffect?
Ans.
Greenhouse effect is caused by the buildup of carbon dioxide and methanein the atmosphere.
A greenhouse or glasshouse has clear walls which allow light to penetratebut prevent heat from escaping.
9. What types of products contain chloroflurocarbon? Suggest some waysto avoid using them.
Ans. Styrofoam cups, food cartons, fridges. Don't buy products in thesecups and obey government warnings on fridges and fire extinguishers.
10. Draw a diagram of the ocean shape showing the following: continentalshelf, continental rise, abyssal plain and ocean ridges.
Ans
See Figure 96.1
11. How much of the Earth's surface is made up of the ocean basin floor?
Ans
The deep ocean floor makes up 70% of the oceans floor
12. How do salts get into the oceans?
Ans
The water from thew land dissolves the salt and mineral in rocks andthis is washed into the oceans. Some areas of the earth contain more mineralsalt than other areas. The dead sea is the saltiest sea.
13. Why are some seas more salty than others?
Ans
Some are more enclosed by mountain ranges, some by latitude and someby nearby salty landmasses. (Some have a high evaporations rate and somehave a high concentration of salt on the land).
14. What are nodules and what minerals are found in them?
Ans
Some countries are now mining mineral nodules (small clumps of mineral),found on the deep ocean floor. These nodules are rich in magnesium, coppernickel and cobalt.
15. How many grams of rock have been weathered to make up a litre ofsalt water?
Ans
Geochemists who study the chemistry of the Earth and the oceans calculatethat the salt contained in one litre of sea water would have been extractedby weathering of 600 g of rock and dissolving all soluble parts.
16. a. What are trace elements?
Ans
Trace elements are elements found in seawater in very small amounts
b. What are the two most abundant elements in the sea?
Ans
The most abundant elements in the oceans are chlorine and sodium
17. Many marine creatures have very high levels of trace elements intheir bodies. Explain how they obtained these minerals.
Ans
Many creatures can extract and concentrate elements from the water bybioaccumulation
18. What is bioccumulation and why is it a problem for humans who eatseafood?
Ans
Many marine algae and some fish have very high concentrations of thesetrace elements in their bodies because they are able to extract them fromthe ocean in a process called bio-accumulation.
For example oysters concentrate zinc in their tissues and lobsters concentratecopper in theirs.
Bio-accumulation can create health problems. People living in a smallJapanese coastal village called Minamata were devastated by mercury poisoningthe late 1970s when pollution from local industry entered the local seafood.The oysters the villagers ate had accumulated high levels of mercury intheir tissues which then affected the humans.
19. Describe two methods of obtaining energy from the sea.
Ans
From waves or tides
20. What information on the oceans can be obtained from satellites?
Tidal currents, ocean currents, surface temperatures or plankton distribution
Use the library to research the following.
1. Under what reference number would you find a book on the followingtopics?
a. oceanography
b. the water cycle
c. continental drift
Suggestions
See your school library catalogue
2. Use the reference encyclopedias to research these people:
a. Alfred Lothar Wegener (18801930)
b. Fridtjof Nansen (18611930)
c. Sir Charles Lyell (17971875)
Suggestions
Use encyclopedias
3. How did the major oceans of the world gain their names?
Suggestions
Use encyclopedias
4. Use an atlas to locate the names of the waterways joining the majoroceans.
Suggestions
Use encyclopedias
5. Research one of the following topics and prepare an oral report:
a. the development of oceanography
b. the detection and prediction of earthquakes
c. the removal of minerals from the oceans
d. the process by which gold can be extracted from salt
e. the different ways in which people use and abuse our oceans
f. why it's important for all nations of the world to be involved inthe drafting of policies which affect our oceans.
6. Surf the mining company web pages by typing 'petroleum' into yourfavourite search engine.
Suggestions
Use the web
1. buoyancy
2. temperature
3. volcanic
4. atmosphere
5. hydrological
6. evaporation
7. carbon dioxide
8. space
9. greenhouse
10. Chlorofluorocarbons
11. aerosols
12. plastic packaging foam
13. waves
14. Satellites