Where did the water in the ocean come from?
Objectives:
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1. The students will be able to explain the water cycle process.
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2. The students will be able to demonstrate and explain evaporation and condensation.
Materials:
Enough of the following for students to work in pairs;
Clear colored jars or bottles with a small neck
Ice cubes
Hot water
An overhead transparency of the following page, The Water Cycle. Be sure to color the drawing in after you’ve made the copy.
Sufficient copies of the Water Cycle Flow Chart
The Experiment Form
Procedure:
Scientists believe that while some water was originally on earth, more came from water vapor in the atmosphere, and from water in rocks that was released during the earth’s formation. Rainwater was released from clouds in the atmosphere (what we refer to as part of the water cycle). As the earth cooled, more water came up from volcanoes, hot springs, and other sources. Gradually our oceans were filled.
Show the overhead transparency on the following page titled, The Water Cycle. Go over the four steps with the students. If the students have no questions at the end of the explanation, shut the overhead off and give each student a copy of the hand out on the following page, A Water Cycle Flow Chart. Read the directions to them and have them fill it in correctly. Directions: The steps that are on the Flow Chart are listed out of order. You are to rewrite them on the chart in the correct order. After allowing sufficient time, correct the flow charts together if you do not wish to collect them.
Explain to the students the experiment they are about to do will (should) allow them to see evaporation and condensation.Have them work in groups of two, and remind them to record their observations on the Experiment Form.
Directions:
1. Place a small amount of hot water in the bottle or jar.
2. Place an ice cube over the top of the bottle (in the neck) so it won’t fall in.
3. Write down your observations.
Follow Up:
Discuss and explain what happened. Explanation: After the ice cube was on the jar a while, they should have been able to see a cloud near the top of the bottle. Water vapor was in the bottle because the warm water inside was evaporating. Water vapor is warm and the air near the ice cube is cool. When the water vapor meets the cool air near the ice cube, it starts to condense. It changes back to tiny droplets of water. The water droplets make the cloud that you see. If the water droplets get big enough, some of them might fall to the bottom of the bottle.
Closure:
Ask, how might our experiment be like what happens with rain? Students should know that not all experiments work all the time. If this experiment does not give you a cloud, try to find out why not. (NOTE: This experiment does not always work, but that is also a valuable lesson.)
ACTIVITY:
Ask the students to come up with a simple experiment that shows evaporation and condensation. (NOTE: It could simply be a glass of water set out on the table. The students should measure the water first, and again in a few days to show evaporation.) Allow them to work in small groups or independently. An experiment form must be filled out. Results could be shared orally with their peers.
Why is the ocean blue?
The ocean often looks blue because of the sun’s shining on the tiny particles suspended in the water. Along the shores of some areas the water looks green because of the blue water being mixed with the yellow pigments present in floating plants.
Is it light or dark in the ocean?
The upper part of the ocean has a lot of light. The deeper you go in the ocean, there is less light. The sunlight goes down approximately 2000 feet (about 600 meters). However, the scientists who went to the deepest part in the ocean aboard the Trieste, a , bathyscaphe, reported a little sunlight as far down as 3280 feet (1000 meters).
ACTIVITY:
Have the students look up information about bathyscaphes and the Trieste, and write a brief report.
How warm or cold is the ocean?
We have learned that the sun lights up the upper part of the ocean. The sun also does something else to the water; it warms the water, or makes its temperature rise.Since the sun does not reach the deep ocean water, that water is colder, and has a lower temperature than the surface water.
The temperature of ocean water near the surface may also be different at different places. For example, near the equator the ocean water is warmer than in the ocean near the North Pole.
The temperature of water changes more slowly than the temperature of air or land. It takes the sun a longer amount of time to warm the ocean than it does to warm the air or land. The ocean also takes longer to cool off once it is warm.
ACTIVITY:
Have the students make a graph with the following information titled Ocean Temperatures at Different Depths. Write the information on the chalk board. At the surface zone, at a depth of 30-200 meters (100-650 feet), the average temperature is 18° C (64° F). In the next zone, the zone of decreasing temperatures, at a depth of 200 meters to 900 meters (3000 feet), the average temperature is 18° C to 0° C (32° F). The last zone, the zone of uniform temperature, at a depth of 900 meters to the ocean floor, has an average temperature of 0° C .
Which ocean is the largest?
The largest ocean is the Pacific Ocean. Covering between 63-65 million square miles, this huge body of water is larger than the land area of all seven continents combined. At its widest point it is about 11,000 miles across. The waters of the Pacific Ocean touch the shores of five continents and more than 10,000 islands.
How deep is the ocean? How do we know?
The average depth of the oceans is about five times the average elevation of the land. In general, the continents stand about three miles above the ocean floor. In 1962, a depth of 35,800 feet was recorded in the deepest-known part of the ocean, the Mindanao Trench (also called the Marianas Trench) east of the Philippine Islands. If the world’s highest mountain, Mount Everest (29,141 feet) were to be placed into this trench, it would be covered by over a mile and a quarter of water!
People found they could measure the ocean depth by using echoes. Sound waves were sent into the ocean from a ship. The sound waves hit the ocean bottom and bounced back to the ship, where people kept track of the number of seconds it took for the sound to bounce back. This helped to determine how deep the ocean was at that point. Measuring the ocean depth in this way is called sounding.
What does the ocean floor look like?
By sounding, people were able to get an idea of what the ocean floor looked like. For example, they would know that the ocean floor was sloping down in part of the ocean. These measurements were recorded on a chart as the ship moved in the ocean.
The ocean floor is divided into three main parts. The continental shelf is the gently-sloping, underwater area which is really an extension of a continent. Continental shelves usually end at depths of 600 feet or less. At this point the ocean floor drops sharply. The bottom may drop 1-2 miles (3-4 km) or as much as 4-5 miles (6-8 km).This is known as the continental slope. The slope ends at the bottom of the ocean, in the part of the floor called the basin.
Gigantic mountain ridges are in the ocean basins. These ridges, when put together, can make up mountain ranges up to 40,000 miles long.
Volcanoes also rise from the ocean floor. Some break the surface of the ocean and form islands. For example, the Hawaiian Islands are the peaks of volcanic cones.
The deepest parts of the ocean, trenches, are cracks in the ocean basin. Seven Grand Canyons could be piled up on the top of each other in many of the trenches without reaching the surface of the water.
Many people think of the ocean as huge holes filled in with water. But the floor of the ocean is probably the true surface of the earth and the continents like islands extending above the ocean. The ocean bottom is made up largely of a rock called basalt. The continents lie on a base of granite, that is lighter then basalt. Scientists think of the continents as if they float on the heavier basalt rocks.
As the land is worn away and deposited in the ocean, there is a gradual change in weight balance. The continents become lighter while the ocean floor is weighed down. Land area rises and the ocean basin settles. A balance is maintained.
The drawing on the following page is for teachers reference only. Scientists have not ‘sliced’ through the earth, and drawings of this type, while used visually to explain the ocean floor, are conceptual rather than actual.
What is in the sediment on the ocean floor?
The ocean floor is mostly made up of soil and rocks washed into the ocean by rivers, streams, winds, and waves; ash and lava from volcanoes; and the remains of marine organisms. The ocean currents, wind, and ice transport these materials.
Most of the ocean’s sediments (such as sand, mud, and clay) come from the land, leaving the thickest deposits in the waters near land. These are generally coarse while those in the deep ocean are generally finer.
The deep ocean floor has relatively little sediment of land origin. The water circulation enriches certain top layers so that biological production is unusually high. Micro-organisms live and die in great numbers, and their remains fall to the ocean floor to form carpets of sediment.This sediment usually found in very deep water is called ooze. All these remains are usually the size of mud and sand. The ecology of these sediments can reveal the earth’s recent history.
Volcanoes also may form deposits on the ocean floor. For example, if the volcano forms an island, volcanic rock may be broken down by waves into particles of boulder, gravel, sand, mud sand, or mud (the ash from the volcano may settle on the ocean bottom as mud).
How salty is the ocean?
The amount of salt in the world’s oceans vary between 33 to 37 parts per thousand. The Atlantic Ocean is the saltiest, with the Pacific Ocean the next saltiest, and the Arctic and Antarctic the least salty. The most salty water is found in waters where there is a minimum of rainfall or river runoff, and high evaporation. Water is the least salty where large quantities of freshwater are supplied by melting ice, rivers, or excessive rainfall.
The sea is slowly but constantly increasing its salt content. Scientists believe that life began in the oceans with, perhaps, the earliest living things, noncellular creatures, surrounded by ocean water. They received their food and oxygen directly from the ocean .
(figure available in print form)
As time passed, plants and animals became more complex and developed an internal fluid which was very similar to seawater. Scientists believe this fluid had remained almost the same during the years, 1% salt. The ocean is more than three times as salty. Using these facts led to the conclusion that the salt content in the ocean is increasing.
