Geochronology as an Aid to 
Study of Arid Lands 
TERAH L. SMILEY 
Laboratory of Tree-Ring Research, University 
of Arizona, Tucson, Arizona 
Researches into past climate have yielded information which 
illustrates that local climate is ever changing. The degree to which 
this change occurs varies in time and in area. First attempts to 
define climatic areas, or areas wherein the climate is essentially 
homogeneous, met with about as much success as first attempts 
to define the size and shape of an amoeba, both being equally 
fluid and equally alive, appearing never to repeat themselves in 
exactly the same pattern or shape. Additional research brought to 
light the fact that in both studies there is more than meets the 
eye, there is cause and effect which has to be determined and 
understood. Geochronology can aid in understanding the effects 
of climate although it cannot help in determining the cause. 
Geochronology 1 is operationally defined as a field of study en- 
compassing all scientific methods which can be applied to the 
dating of terrestrial events. Climatic change 1s an event which 
falls within this category. These methods are used to date changes 
which have occurred over long periods of time to determine the 
duration of change, the length of visible climatic patterns, and the 
recurring climatic cyclics so we may view them in their proper 
perspective and weigh them accordingly. No evidence of what 
might be called a true cycle has been discovered even with recently 
refined dating techniques. All evidence indicates a variable (in 
time and in intensity) cyclic-like pattern of change which can 
only be interpreted on a relative scale. One specific approach, 1.e., 
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