People who examine the past often use what are called proxy data. These are things that don't directly record past conditions that we want to know about, but which allow rational inferences. For example, fossil plants and animals often let us make informed estimates of past temperatures and precipitation patterns from our knowledge of requirements of living relatives.
Different proxies give different perspectives. Plant parts gathered
into middens by packrats and preserved for tens of thousands of years give information
on past vegetation growing within a few hundred feet of the middens—a very local
picture. Plant pollen, preserved in pond sediments, comes from miles around the
deposition site, blown in by the wind. Pollen, then, tends to give the big picture—the
regional scene. Animal fossils concentrated in cave deposits, often the result of
carry-ins by owls, tend to be drawn from within a 2 to 3-mile radius, filling in the
middle range. Proxy data such as these allow us to assemble a dependable, though
slightly fuzzy, picture of the Chihuahuan Desert's past.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.