By Boak Wiesner
There are things in nature and in life that follow regular patterns whereas there are other events that do not. As I drove in, the sun, playing in the water of the fountain, was creating rainbows that my eyes could see. Rainbows are the quintessence of ephemeral. They happen only when specific conditions of droplet size, the angle of the sun with respect to the observer, and the angle of incidence coincide.
But seeing it reminded me that school had started for another year and that it was because of how I could explain how rainbows are produced through refraction and total internal reflection to the principal who soon hired me to teach those many years ago. The school year is a cycle that follows the sequence of farm crops which matches that of grasses. Someone along the way in our human realized that if one just stayed in place for one year, another crop of seeds would fall, with some to eat and some to plant and thus agriculture and civilization emerged.
As it was getting hot, I descended into what has become my favorite area of the Arboretum, the ravine. So many folks walk on by in the hot sun along the Three Mile Drive while immediately next to them, off the hot tar, small trails lead down into the shady, cool quiet of the ravine. While I might have been the only human, squirrels were everywhere. I wondered if any of them were the young that had been born in the hollow tree that I pictured in a previous installment. The birth and maturation of animals follows a cycle.
The very presence of the ravine got me thinking about its formation, to me an ephemeral event, because just once will a ravine be formed right smack dab here on the earth’s surface. The glacially deposited moraine that running water had cut into the ravine could happen again and again if the conditions are right but the chances against a ravine right here again are great.
Four major periods of glaciations* have happened in the past few million years and one would think that the celestial mechanics producing them would represent a long-term cycle, which it does, but only up to a certain point. Considering that the continental plates drift around quite erratically up here on top of the chaotically liquid mantle, Ice Ages only happen when there’re sufficient landmasses at high enough latitudes to support the ice.
*An archaeologist friend of mine passed along a nice mnemonic concerning the sequence of these four: “Never Kiss an Illinois Woman”, that is Nebraskan, Kansan, Illinoian, and Wisconsonian. Handy, huh?
Boak Wiesner is a Minnesota Naturalist volunteer.