Some 20,000 years ago, our Chihuahuan Desert was a much different place. That was the height of the last ice age, and while ice sheets covered much of the northern part of the continent, our region enjoyed cooler temperatures and more moisture. The last ice age was only one in a series extending back over the nearly 2 million years of the Pleistocene, and other, earlier ice ages affected Mother Earth, as well.
But why ice ages? We're far from knowing all the details, but most think that our wandering continents are partly to blame. Antarctica moving over the South Pole allows ice to accumulate year after year, while the North Pole now lies in an ocean basin nearly surrounded by land, capturing cold water and ice.
With these conditions in place, astronomical processes take over. The
rocking back and forth of Earth's axis, changes in the shape of Earth's orbit,
and changes in the timing of nearest approach to the sun seem involved. When all come
together just right, the ice sheets grow and the desert blooms again.
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.