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OverviewWith this activity, students begin their exploration of aquatic environments. The unit begins with an introduction to the different types of water bodies on Earth and the ways in which water moves and carries. |
MaterialsOcean Currents Map |
BackgroundLife Began in the WaterScientists believe that life first evolved in the oceans. From single-celled to multi-celled, life developed in close contact with water and the gases and nutrients it carries. Some scientists even believe that much of the evolution of life on land, and the development of plant and animal circulatory systems, resulted from the need to have water available—both to prevent cells from drying out and to use as the basis for their chemical reactions. The Present-Day OceansOver the course of Earth's history the shape of oceans has changed. The Atlantic Ocean was the latest ocean to be formed, created when Africa split away from North America about 200 million years ago. Magma rising in the Mid-Atlantic trench caused spreading of the sea floor and a general westward movement of the North American plate. Lakes are younger, generally formed by retreating glaciers. The oldest lake, Lake Baikal in Russia, is only 25 million years old. The Ice AgesScientists have accumulated evidence suggesting that the Earth's surface has experienced regular episodes of cooling (when water was bound in ice caps) and warmth (when ice caps and glaciers melted and retreated) for at least the last half-million years. This evidence has included sample cores of ocean sediment, the pollen preserved in peat, and oxygen isotopes bound in the shells of microfossils. The Hungarian scientist Milutin Milankovitch believed that small changes in the Earth's orbit and tilt on its axis may have caused what are now known as the ice ages. This argument has gained the support of other scientists, many of whom believe that variations in the Sun's energy output might also be a factor. The last ice age ended about 14,000 years ago, having lasted about 60,000 years. The Earth has been warming since then, including discernible increases in our own time caused by, almost all scientists agree, human activities. You may want to draw on students' exploration of plate tectonics during this discussion. As always, a historical perspective is important. Note the Isthmus of Panama. Before North America and South America were joined, the Atlantic and Pacific Oceans were connected. Some important features for students to notice include the gyres of rotating currents (clockwise in the north, counterclockwise in the south), the offset to the west of the gyres, the way water streams up the sides of continents, and the direct flows of the circumpolar and equatorial currents. |
Classroom Management and PreparationThe first two steps of this activity are designed as a class forum. The Spill Case Stories in Step 3 can be done by the class as a whole, by student groups, or by individual students as homework. You might prefer to make teams, give them cards with cargo that float and locations of spills, and ask them to trace on a map where they think they might end up. (There are no perfect answers so much as better reasoned answers.) Student PreparationThe World's Waters |
Recommended Procedures1. Have students consider the distribution of water on Earth.Using the world map and remotely-sensed images on the Web, have students locate the major bodies of water and consider their distribution on Earth. Are all waters interconnected? What unique aquatic features do students notice in the global images? Is water equally distributed around the globe? Has it always been this way? This first exploration of global waters should focus on the major ocean basins (North and South Atlantic, North and South Pacific, Indian Ocean), the great freshwater lakes (Baikal, Tanganyika, the Great Lakes in the United States), the salt lakes (Dead Sea, Utah's Great Salt Lake, Central Asia's Aral and Caspian Seas), and the largest river basins in each continent 2. Consider the availability of fresh water.(While this topic will be dealt with at the end of the water unit in more depth, it is important to touch upon it frequently.) Where fresh water is stored? (streams, rivers, ponds and lakes, ice caps, clouds, water vapor, groundwater, and soil moisture). Why is this important? Who has safe drinking water? Imagine you had a grant to deliver water to people who need it. Where are they and how do you deliver it? 3. Have students examine the map of surface ocean currents.What do they notice? You can have them describe three key features of the currents in their journals and then share their findings. Some important features for students to notice include the gyres of rotating currents (clockwise in the north, counterclockwise in the south), the offset to the west of the gyres, the way water streams up the sides of continents, and the direct flows of the circumpolar and equatorial currents. Here is a good map: You might want them to study convection. 4. Challenge students to follow the Spill Case Stories.Either in groups or as a class, have the students consider the mysteries in the Spill Case Stories. The piece describes two stories of objects spilled on the ocean. In each case, students have to answer a set of questions about the spills. Students can draw the path of the spills using different colored pencils for different spills. As they try to determine these paths, they may want to keep a list of variables that could affect where the spills travel. There are a variety of Web sites dedicated to tracking spills such as those described in the Spill Case Stories. Students can use these sites to research older spills and track new ones. |
AssessmentStudents' responses to the Spill Case Stories provide an opportunity to assess students' ability to reason through a problem using a map as a problem-solving tool. |
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The World's Waters (teacher guide)