1. HOW DOES SOIL FORM?
GLOBE NY Metro, 2008

2. Why do we study soil? Because It’s A(n)
Great integrator
Producer and
absorber of gases (CO2 and others)
Medium for plant growth
Medium of crop production
Home to organisms
(plants, animals and others)
Waste decomposer
Snapshot of geologic, climatic,
biological, and human history
Source material for construction,
medicine, art, etc.
Filter of water and wastes
Essential natural resource
Medium of heat and
water storage

3. Soils are very different, depending on how they form
United States Department of Agriculture

4. 5 FACTORS CONTROL THE TYPE OF SOIL
TIME is the 5th factor Soil forms by the interaction of the first four factors. It changes to create soil profiles unique for the conditions and elapsed time. A soil profile consist of layers called “soil horizons”
4 factors control soil-forming processes
Living things
Climate
Topography
During the GLOBE Soil Characterization protocol, you will describe, sample, and analyze soil horizons near your school
Parent Material
Photo courtesy, Ray Weil, PhD

5. ROLES OF THE FIVE FACTORS OF SOIL FORMATION
Living things: Plant roots physically break rocks into small pieces; lichen dissolves rock; burrowing animals mix the soil and help aeration
Climate: heat and water accelerate chemical changes (so moist, temperate areas like NYC have different soils than arid, tropical, or polar areas).
Topography: Loose soil stays in place in flat areas, allowing more thorough physical and chemical alteration of its grains. On steep slopes, the soil moves downhill before complete alteration can occur.
Parent material: Chemical changes during soil formation depend on what minerals and rocks are present. Example: Calcium-rich soils generally form from calcium-rich rocks (like limestone) but not from calcium-poor rocks like granite.
TIME: When bedrock is exposed at the surface, chemical, biologic, and physical processes combine to produce a thin soil layer. Over time, the processes extend vertically downward, developing soil horizons whose position and thickness change over time.

6. Coniferous forest soil Tropical rain forest soil
If all five factors are the same in two geographic regions, the soil will be the same in both. Some basic examples of different soil types include:
Temperate deciduous soil
Coniferous forest soil
Grassland soil
Tropical rain forest soil
Desert soil

7. Soil is an excellent place to study interactions in the Earth System, including contributions from the
Atmosphere • Dew (moisture from the air) begins chemical alteration of parent rock • Rain erodes loose soil, preventing further alteration • temperature controls rate and extent of chemical processes
Hydrosphere • Water seeps into the ground, dissolving and redistributing elements • evaporation dries soil, changing its physical characteristics
Biosphere • plants add and remove chemicals • plant roots anchor soil in place, enabling chemical reactions to be completed • animals mix soil; transport seeds, etc.
Geosphere • solid rock and unconsolidated sediment are the parent material for soil • geologic processes (surface and internal) expose and bury rock, etc.

8. Hydrologic Cycle and the Soil
Soil Properties related to the hydrologic cycle.
Soil moisture
Color
Temperature
Structure pH
Texture
Horizon
Depths
Bulk Density