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Day 112: Dichotomous Keys February 16, 2007

Posted by Admin in Geology.
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Classifying objects (such as minerals, animal species, or paperclips) into different groups based on their indentifying characteristics was the main objective of today’s lab on constructing a Dichotomous Key.  What does that mean?

DichotomyA division into two usually contradictory parts or opinions.

The example we completed in class involved seperating the following six animals:  eagle, brown bear, ostrich, shark, polar bear, gold fish.  Alll six animals begin in one large grouping and we must divide them into two groups based on their characteristics.  Most classes chose to divide the animals into those that live mainly on land (eagle, ostrich, brown bear, polar bear) and those that live mainly in water (shark, goldfish).  We then broke each of those groupings down into smaller groups based on some other characteristic.  For instance, the land animals can be further divided into those that have fur and those with feathers.  The water animals can be seperated by color.  The end result is a concept map (graphical representation) of an identification key that can then be used to identify each individual objecd based on its characteristics.

The lab that was completed in class consisted of constructing a dichotomous key to identify ten different types of clips:  butterfly clips, paper clips, binder clips, brass fasteners, etc…  The lab was due at the end of class and worth 10 points.

Next week we will aim to identify 10 mineral samples by using a large dichotomous key that characterizes minerals based on those properties we defined earlier in the week:  breakage, hardness, color, streak, transparency, density, etc…

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