Soil, how formed (teach)


Published on

This slide show can be used as an introduction (or review) for elementary science students on how soil is formed.

Published in: Education, Technology, Business
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Soil, how formed (teach)

  2. 2. Hey, listen to this. Have I got the dirt on.... SoilBy Moira Whitehouse PhD
  3. 3. 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.
  4. 4. Here we see a slab of Earth taken out ofthe crust with the soil on top showingwhere we live. Soil, from the bedrock to the top, is our subject. There are different layers of soil—similar in characteristics such as composition, texture, and color. Bedrock (crust of the Earth) USDA
  5. 5. Thankfully, soil covers most of the Earth’s solidcrust (bedrock); however, in some places it isthin or nonexistent. 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.
  6. 6. Speaking mainly of top soil and the upper soil horizonsSoil is made of.....? Four things:
  7. 7. • weathered pieces of rock made up ofminerals (All rock is a mixture ofminerals.)• organic material (remains of dead plantsand animals)• air (containing oxygen)• water
  8. 8. The weathered rock pieces(minerals) make up abouthalf of the total mass ofmost soil.Less than 10% is organicmatter-- dead plants andanimals.The other half is made up of many, many,interconnecting holes between the rock piecesand organic matter.Depending on location, the time of year or rainfall,these holes, called pores, are filled with either airor water.
  9. 9. SoilTiny pieces of Remains of Air with oxygen Waterweathered dead plants rock and animals In pores, spaces between the pieces of weathered rock air water
  10. 10. Those ingredients that make up soil are necessaryfor the plants and micro-organisms that live there.• The weathered pieces of rock and the organicmaterial provide many of the nutrients such asiron, nitrogen, potassium that plants need to growand to carry out their life processes. • Plant roots and soil microorganisms get the oxygen and water they need to live from the spaces (pores) in the soil.• The weathered pieces of rock anchor the plantsroots so a plant doesn’t blow or wash away.
  11. 11. In this presentation we will focus mainly on thesolid parts of soil—weathered rock and thehumus—the organic material (dead plants andanimals). Soil: Weathered rock Humus—organic matter (tiny pieces of rock) (remains of dead plants and animals)
  12. 12. First we will explore the weathered rock partof the soil.Weathered rock is formed through the processof weathering which breaks rock into smallerand smaller pieces.Weathering is caused by agents in nature(wind, water, temperature variations) thatbreak rock down into smaller pieces.
  13. 13. In review, what is weathered rock?Pieces of rock that have been broken downinto smaller pieces by the forces of nature—water, wind, ice, acid water, plant roots, etc.are called weathered rock.These pieces of rock may be the size of aboulder or a grain of sand.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.
  14. 14. The weathered rock in soil probablystarted out as a huge boulder.In the process of being broken down, thesize of the particles of rock becomesmaller and smaller—boulders to largerocks, to smaller pieces of rock topebbles to sand, silt and clay.
  15. 15. Over hundreds, maybe thousands of years, it could have happened something like this. SoilSoil
  16. 16. Looking again at the solid part of soil, first we will consider the three types of soil that are the result of weathering: Soil: Later we will discuss humus. Weathered rock Humus (remains of dead plants & animals) Sand Silt Claylargest smallest particles
  17. 17. These three types of soil, sand, silt and clayare identified largely based of the size oftheir weathered rock pieces. 1. Sand—largest particles2. Silt—medium sized particles3. Clay—smallest particles
  18. 18. The following guidelines are use totalk about the different sized particlesof sand, silt and clay.
  19. 19. Size of Particles of Rock (Diameter)•2 m boulders• coarse fragments such as pebbles > 2 mm• sand < 2 mm to 0.05 mm• silt< 0.05 mm to 0.002 mm• clay < 0.002 m
  20. 20. Wikipedia Commons
  21. 21. Still looking at the solid part of soil, we now examine the humus: Soil: Weathered rock Humus (remains of dead plants & animals) Sand Silt Claylargest smallest particles
  22. 22. What is humus?The organic part of soil—that which was once living.How is it formed?Humus is formed when dead plantsand animals decay.
  23. 23. What causes these dead things to changeinto soil?Special organisms in the soil, calleddecomposers, cause dead plants and animalsto decay or rot changing their bodies into thehumus part of soil.When plants and animals die, they become foodfor these decomposers--bacteria, fungi, arthropods, nematodes andearthworms. recycle dead plants and animalsDecomposersinto nutrients plants need.
  24. 24. Bacteria are the smallest living organisms,and the most numerous of thedecomposers.A teaspoon of fertile soil generallycontains between 100 million and 1 billionbacteria.They carry out the majority of decomposingthat occurs in the soil.
  25. 25. http://soils.usda.govMagnified bacteria found in the soil.
  26. 26. Fungi is the name for simple organismsincluding mushrooms, molds and yeasts.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 decompose dead plants and animals.
  27. 27. Mushrooms growing on logs
  28. 28. Mushrooms growing on a forest floor mill56 Mushrooms growing in dead grass photogirl7
  29. 29. beginning to decompose leaf veinsin grass clippings.
  30. 30. Other important decomposers found inthe soil are numerous invertebrates—animals without backbones.The initials “FBI” can be use to help usremember the three main decomposerstypes:—fungi---bacteria---invertebrates.Invertebrate decomposers include wormscalled nematodes, mites, pillbugs andmillipedes.
  31. 31. Nematodes, a group of invertebrate decomposersliving in the soil are tiny non-segmented wormstypically 1/500 of an inch in diameter and 1/20 ofan inch in length.One square yardof woodland oragricultural soilcan contain upto severalmillion Nematodes magnified in soil.
  32. 32. Other importantinvertebratedecomposersPill bug
  33. 33. Decomposing mitesMillipedes
  34. 34. Organisms such pill bugs, millipedes and mitesare important to the soil because they stir upand churn the soil, mixing in air which isneeded by other organisms in the soil habitat.They shred organic matter into small pieces,assisting other soil organisms in thedecomposition process.The lowly earthworm is also an importantdecomposer.
  35. 35. Earthworms eat dead plants andanimals, thereby, absorbing thenutrients that they need tosurvive.Earthworms excrete wastes inthe form of casts whichare rich in nutrients such asnitrogen and phosphorous thatplants need.In addition to breaking down organic materials andadding nutrients to the soil, earthworms also helploosen the soil, thereby, creating space for the oxygenthat plant roots and microorganisms need to live.
  36. 36. Decomposition creates soil that containsthe nutrients plants need in a form that theycan use to carry out their life processes. USDA
  37. 37. The cycle of plantsabsorbing mineralsfrom the soil and andthese minerals beingreturned to the soilthrough decompositionis repeated over andover in nature. angus clyne
  38. 38. Where there is lots of plants to decay and enrich thesoil, such as in deciduous forests and grasslands, thesoil is rich in humus and very fertile. Wikipedia Commons
  39. 39. Wikipedia Commons Cory Leopold Desert in Saudi Arabia The Chihuahuan Desert along the Rio GrandeWhere there is little or no vegetation toprovide the organic debris, such as at theseashore or in the desert, the soil has little orno humus and is not very fertile.
  40. 40. In review, we learned that soil is made upof four main things. Can you rememberthem? (two solids, one liquid and one gas)
  41. 41. SoilTiny pieces of Remains of Air with oxygen Waterweathered dead plants rock and animals In pores, spaces between the pieces of weathered rock air water
  42. 42. Next, what do we call tiny particles ofweathered rock?Yes, we call them soil.What are the three main types of soil thatresult from weathering of rocks?Sand, silt and clay What is the main feature that distinguishes sand, silt and clay?The size of the particles, sand being thelargest and clay the smallest
  43. 43. Weathered rock makes up one part of solidsoil. What makes up the other part?Yes, it is humus.What is humus?The organic part of soilwhich was once living.How is it formed?Humus is formed when dead plantsand animals decay.
  44. 44. This stuff is an important natural resource for man.When we love andhonor it we call it soil.
  45. 45. But when grownups don’t like it, they call it dirt or mud.