BACKGROUND:

The soil specimens that the students have looked at come from two sides of the San Andreas fault in California.  The San Andreas fault has moved one side relative to the another and has allowed different types of rocks to abut right next to each other. On the worksheet you can see that west of the San Andreas and Pilarcitos Faults, there are granitic rocks. East of the Pilarcitos Fault you have rocks composed of serpentinite.

The parent rock material weathers, releasing the elements that compose the minerals of the rocks.  It is these elements that provide nutrients for the plants to grow. Students will see in LIFE CYCLE - NATURAL ENVIRONMENT (6B) that the plants are very different.   The rock serpentinite is composed mainly of the mineral serpentine.  The principle minerals of the serpentine group all have the approximate composition H₄Mg₃Si₂O₉, The principle minerals in a granitic soil are quartz, feldspar, hornblende, and mica.   

The factors that influence soil formation include climate (particularly temperature and precipitation), living organisms (especially native vegetation and human beings), the nature of parent material (including texture and structure, and chemical and mineralogical composition), topography of area, and time that the parent materials were subjected to soil formation.  

The process of disintegration of solid rock makes possible a foothold for living organisms.  Decomposing minerals release nutrients that nourish simple plant and animal forms.  Rocks are broken down by mechanical or chemical mechanisms.  Mechanical weathering  or disintegration  is effected by  temperature (differential expansion of minerals, frost action), erosion and deposition (mainly by water, ice and wind), and plant and animal influences.  Chemical weathering or decomposition can be accomplished by the chemical processes of hydrolysis, hydration, acidification, oxidation, and dissolution.  It is the chemical weathering that frees elements into an ionic state that makes them available for plants to use.

PROCEDURE:

1. As the students complete their worksheet, have them refer to Life Cycle - Natural Environment 6A Pre for the chemical composition of the minerals.
     
2.  ANSWERS: 
   3. serpentine;  
   4. quartz, feldspar (mainly) could include biotite, hornblende, pyroxene;  
   5. Mg,Si,O,OH;  
   6. Ca,K,Al,Si,O;  
   7. Ca,K,Al;  
   8. Yes, plants have different requirements.