Weathering and Soil Formation Chapter 10 Weathering and Soil Formation

Chap 10, Sec 3 (From Bedrock to Soil) Objectives: Describe the source of soil. Of what is soil made? What are the layers in the soil profile and what is their function?

Tech Terms: soil – a loose mixture of geologic (inorganic material - rocks) and biologic (organic material – dead animals) that supports the growth of plants. **The amount of sand, silt, and clay, determine a soil’s texture!!!**

(Copy the particles & sizes here from Fig 2 on pg. 289)

2. soil horizons – layers of soil that differ in color and texture from the layers above and below.

*Because soils are made from weathered rock fragments, the type of soil that forms depends on the type of rock that weathers.* (For example: Granite of Stone Mountain vs. Limestone of Hilton Head Island)! CAN YOU THINK OF OTHERS?

O horizon (litter) – organic, slightly decomposed material from fallen leaves, plants, and animals. A horizon (topsoil) – near surface, and contains the MOST humus of any layer (nutrient rich) E horizon – zone of eluviation and leaching (downward movement of dissolved material)

B horizon (subsoil)- contains little or no humus. C horizon (weathered parent material) - contains only weathered rocks and minerals that come from the bedrock layer beneath. R horizon - bedrock

Soil Horizons WS: O – This is the top layer, the “organic” layer which is made up of dead plant matter for the most part. A – This is the second layer of soil, what we call the “top soil”. It too has lots of organic matter mixed in and is usually darkly colored. B – Subsoil layer. There isn't much organic stuff in here. Sometimes the transition between top soil and subsoil is very sharp and defined and sometimes they fade into one another. C – This layer usually has lots of large rocks mixed in with soil deep underground. D – This is the bedrock that lies beneath the soil. In some places this can be quite near the surface and in others it is very, very deep.

soil fertility – the ability of soil to hold and supply nutrients to a plant. humus – dark, organic material formed in soil from the decayed remains of plants and animals.

The example below is of Florida soil leaching – when water dissolves and carries nutrients in the topsoil through the horizons. The example below is of Florida soil

In Summary: https://www.brainpop.com/science/earthsystem/soil/