SOIL, HOW IT IS FORMED More elementary than my other SOIL slide show and pitched more for 3rd or 4th grade students. By MoiraBy Moira Whitehouse PhD
The continents have a layer of solid rock, the crust, covering the hot stuff in the mantle.The continental crust, then, is mostly coveredwith thick layers of soil.
Thankfully, soil covers most of the Earth’s solidcrust (bedrock). Why do we care? Plant growth, that allows us to live, occurs on the top layer of soil. layers of Below that layer are soil several other layers, some that D provide minerals and bedrock ores for our use. http://www.nrcs.usda.gov
What is soil made of?Even thoughsoil looks likeone thing, it isreally made upof manydifferent kinds.of things.Two of the main things are: 1. tiny, tiny piecesof rock and 2. the rotten remains of deadplants and animals.
Soil:Tiny pieces of rock) Humus—organic matter (remains of dead plants and animals)
First, looking at that part of the soil that is tiny,tiny pieces of rock.Through the process called weathering bigrocks are broken into smaller and smallerpieces. The smallest pieces are called soil.
People can break rock into smaller pieces with a sledge hammer.But people are not the main reason that rocksare continually being broken up into smaller andsmaller pieces until they become soil.
Weathering is caused in nature by such thingsas wind, water, and temperature changes thatbreak the rock into ever smaller pieces.
The weathered rock in soil at some pointin time started out as a bigger rock,maybe a large boulder.In the process of being weathered, thesize of the particles of rock becomesmaller and smaller—boulders to largerocks, to smaller pieces of rock topebbles to soil.
Big rocks become smaller and smaller and smaller until they are soil.
Over hundreds, maybe thousands of years, it could have happened something like this. SoilSoil
Some rocks break down into smallerpieces more easily than other rocks.Those rocks that are more easily wornaway are called soft.And those that are less easily worn awayare called hard.
Activity to show differences in hardness of rock.•Give the students a small hard rock, a smallpiece of soft sandstone rock, a sugar cube anda piece of chalk. •Ask them to weather therocks by rubbing them against one another.•Tell the students that the chalk and sugarcube are models of rock.Ask the students if some of the “rocks” weremore easily weathered than others. Explainthose rocks are called soft and the ones lesseasily worn are called hard.
Now let us discuss, some of the things innature that cause rocks to break intosmaller and smaller pieces.In other words, what are some of thethings that cause rocks to weather.
One of these things is moving water.Running water in rivers and streams carryrocks downstream causing them to hit oneanother and break apart.
Imagine rocks tumbling along the bottom.As the sand and gravelcarried by the water rubagainst the rocks in theriver, they becomesmooth and rounded andare called river rocks.Notice how smoothand rounded theseriver rocks are.
To see an animation of this process, openhttp://whs.moodledo.co.uk/mod/resource/view.php?inpopup=true&id=26639and choose “click direct link to file”. When finished, close the window to theinternet and you will be back on the slide show.
When a river flows rapidly over a plateau, itbreaks the rocks into smaller and smaller piecesof rock. The fast moving water carries thesepieces of rock down the river creating a canyon. .
The following activity may be used todemonstrate weathering by moving water.•Place a piece of soft sandstone in aplastic jar or vial along with a harder rockand some gravel. •Add some water.•Have the students shake the containerback and forth. •After several minutespour the contents out on a plastic plateand observe what has happened.Discuss how this activity models weatheringof rock due to moving water and rocksbanging together.
Another thing that weathers rock is blowingsand. As it rubs against rocks can break theminto smaller and smaller pieces.
Blowingsand rubsaway thesofter rockchanging itinto soil. The harder rock is left behind.
Activity to demonstrate weathering byblowing sand.•Place a piece of colored chalk and salt ina plastic jar or vial. •The chalk is a modelfor rock and the salt a model for sand.•Have the students shake the containerand then pour its contents on to a plasticpaper plate and observe.Discuss the results of this activity andhow it models weathering by blowingsand.
Water gets into cracks in the rock. If this waterfreezes and melts and freezes and melts timeand time again it can break the rock apart.
To see an animation of frost wedging, open http://www.phschool.com/webcodes10/index. cfm?fuseaction=home.gotoWebCode&wcprefi x=cul&wcsuffix=2052 and play the small video. When finished, close the window to the internet and you will be back on the slide show.
Activity to demonstrate weathering bywater that expands when freezesexpands and can break open a rock.•Place a can of liquid coke in the freezerovernight and observe what happens.Discuss how this activity modelsweathering of rock due to the fact thatwater when it freezes expands and cancause rocks to break.
The Grand Canyon was formed by these threethings in nature: moving water in a river, windcarrying sand, and the repeated melting andfreezing of water in the cracks in the rocks. Colorado River
In review, ...so what is weathered rock?Pieces of rock that have been broken downinto smaller pieces by the forces of nature—water, wind, ice, etc. are called weatheredrock.These pieces of rock may be a huge boulderor the the size of a grain of soil.The smallest pieces of weathered rock iscalled soil.Some of these pieces of rock may be small thatwe can only see them under a microscope.
Now for the other part of soil humus.Humus is the organic partof soil—that which wasonce living.How is it formed?Humus is formed when dead plantsand animals rot or decay.
Bacteria are the smallest livingorganisms, and the most numerous of thedecomposer (living things that causedecay).A teaspoon of fertile soil generallycontains between 100 million and 1 billionbacteria.As they eat the dead plants and animals, theycarry out most of the decomposing thatoccurs in the soil.
http://soils.usda.govMagnified bacteria found in the soil.
Fungi is the name for simple organisms (livingthings) including mushrooms, molds andyeasts.Next to bacteria, fungi are the most efficientdecomposers.Fungi are not plants; they cant make their own food.They absorb their nutrients from the organismsthey are decomposing. In the process they releaseenzymes that cause dead plants and animals to rotor decompose.
http://www.flickr.comBenimoto http://www.flickr.comFuturilla Mushrooms growing on logs http://www.flickr.comscoobygirl
Invertebrates(animals withoutbackbones) are alsodecomposers.Importantinvertebratedecomposers are:Pill bugs http://www.flickr.comzimpdenfis
Activity to show how leaves and other organicmaterial can decompose and form rich black soil.•Place samples of compost on the students’ tablesand ask them to observe. •Be sure to give thestudents samples of various degrees ofdecomposition. •Explain the bacteria that causemost decomposition are too small for us to see.Discuss how dead plants and animals candecompose and change into blackish colored soiland how most soil is a mixture of weathered rockand rotten plants and animals.
So in review: What are two parts of soil? Soil: Tiny pieces of rock Humus—organic matter (remains of dead plants and animals)
What is the process in nature called thatcauses rocks to break into smaller andsmaller pieces?Yes, weathering.What are some forces in nature thatcauses the weathering of rocks?
And finally, you should remember howthe other part of soil, humus, is formed?Soil—it is thedirt we inscience chooseto love.
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