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OLD WATERDidyouknowtheworldhasthesameamountofwatertodayaswhentheEarthformedlongago?AccordingtoGeologists,Earthwasformedabout4.5billionyearsago.Volcanicerup-tionsreleasedvariousgasesandcreatedaprimitiveatmo-sphere—watervaporwasoneofthesegases.AstheearthcooledthevaporcondensedintoliquidandwaterraineddownontotheEarth’ssurfacecreatingtheoceanandseas.Nosignificantamountsofnewwaterhaveformedsincelongago,andthewaterformedthenhasnotdisappeared.TheEarth’sexistingwatermovesaroundtheplanetthroughacomplexwatercycle.Thewatercycleistheendlessmovementofwateraroundtheplanet.Waterchangesfromliquid,tosolidandvaporformasitmovesfromplacetoplaceontheEarth’ssurface,intheatmo-sphereandunderground.
The Water CycleWhere does water come from, and where does it go?
WHAT DRIVES THE WATER CYCLE?Thesunprovidestheheaten-ergynecessarytocausewateronearthtochangestatesandmovethroughthewatercycle.Astem-peraturesincreaseicemeltsandliquidwaterevaporates.Whentemperaturesdecreasewatervaporcondensestoliquidformandliquidwaterfreezestosolid.
STATES OF WATERWaterexistsinthreeformsattheEarth’ssurface:liquid,solidandvapor.Liquidisthestateofwaterwithwhichwearemostfamil-iar.Thisistheformofwaterwedrink,andinwhichweswimandbathe.Watervaporisthegas-eousstateofwater.Watervaporisallaroundus,eventhoughwecan’tseeitmostofthetime.Waterinsolidformiscalledice.Waterchangesfromonestatetoanotherwhenheatenergyisaddedorlost.
ASSESSMENTSPRETEST/POSTTESTBeforestudentsvisitTheWaterCycleUnitoftheDiscover Water website,havethemtakethefollowingquiztoseewhattheyalreadyknowabouthowwatermovesaroundourplanet.Havestudentstakethesamequizagainasaposttesttomeasurelearning.
PleaseseeThe Water Cycle Pre-test/Postteststudentcopypage.
Depending on grade level and ex-pectations, answers could include discussion of flow, soaking in, percolation, consumption, excre-tion, transpiration, evaporation, precipitation and possibly deposi-tion and sublimation.
LEVEL 2Wheredoeswatercomefrom,andwheredoesitgo?
Answers should discuss the idea that all water on earth is recycled endlessly from place to place and state to state through the water cycle.
McDuffie,Thomas.2007.“Pre-cipitationMatters.”Science and Children,44(9),38-42.
Robertson,WilliamC.2005.Air, Water, and Weather: Stop Faking It! Finally Understanding Science So You Can Teach It.Arlington,VA:NationalScienceTeacherAs-sociation.
Shepardson,DanielP.,BryanWee,MichellePriddy,LaurenSchellenberger,andJohnHarbor.2009.“WaterTransformationandStorageintheMountainsandattheCoast:MidwestStudents’Dis-connectedConceptionsoftheHydrologicCycle.”International Journal of Science Education,31(11),1447-1471.
Toft,JoanneandKathyScoggin.2007.“TheRippleEffect.”Science and Children,45(3),21-23.
Vowell,JulieandMariannePhillips.2007.“ADropthroughTime.”Science and Children,44(9),30-34.
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• Discover Ground Water and Springs
• Discover the Hudson River
• Discover the Waters of Nevada
• The Water Story
• Water, Every Drop Counts
ProjectWETActivities
• Adventures in Density
• Blue Planet
• Blue River
• Get the Ground Water Picture
• Just Passing Through
• Snow and Tell
• pringing Into Action
• Storm Water
• The Incredible Journey
• The Thunderstorm
• Urban Waters
• Your Hydrologic Bank Account
ADDITIONAL STUDENT RESOURCES
Cassino,Mark,andJonNelson.2009.The Story of Snow.SanFrancisco,CA:ChronicleBooks.
Hooper,Meredith.2008.A Drop in My Drink: A Story of Water on Our Planet.London,UK:FrancisLincolnChildren’sBooks.