NATURE AS FINGER PAINTER
fascinating patterns shown in cast # 34
were found in a quarry at Westerstetten (near
In the inorganic world, wave ripples (#3) are an example. Here, the distance between crests depends on the distances that sand grains roll to and fro during one wave. Similar, but less linear, patterns emerge in a framed layer of water between glass plates when it is warmed from below. In this case the instability releases convection rolls (Bénard cells), whose diameters depend on the distance between the glass plates. Much larger convections cells in the mantle of our planet appear to be responsible for plate tectonics. Similar spiral or meandering patterns originate in fluids, in which a chemical reaction proceeds in a rhythmical fashion, or in the magnetic domains of a garnet crystal. Other examples are load casts, in which heavy sand has sunk into a soft mud layer underneath, but without alignment.
In the organic world examples of zebra patterns are just as diverse. They reach from brain corals to fur colors and from shell ornaments to the patterns on our own finger tips. The latter have the function to increase the grip and to regulate the distribution of sweat glands and sensory cells in the skin. For these functions, the particular pattern of grooves and ridges is irrelevant, which explains variability comparable to that of the Bénard cells in our experiments. It is a strange paradox that our most unmistakeable identity does not rest on heredity, but on the randomness of a self-organizational process!
these comparisons alone do not explain the Westerstetten sculptures,
an inorganic origin very likely.
Whether or not this fascinating sculpture qualifies as an object of art is another question.
work of a modern artist # 35 illustrates
the flexibility of the term. Similarly, masons in the royal summer
So where is the limit?
Are you an artist when
your hand creates patterns in the glass panel?
Were the Chinese masons artists
when they used a self-organizing process to produce a pleasing design?
the definition of art not be based on perception rather than
|No.34a WAVES OF PETRA
The true nature of the
(# 34) can be better understood by comparing with a phenomenon that is
expressed not by relief, but as color bands in vertical sections
rock. These "Liesegang Rings" are most beautifully developed in the
ancient city of
We know that Liesegang Rings formed long after the origin of the rock by ground water permeating gradually through the pore space. In this process, soluble constituents are taken up and re-precipitated along the advancing front as soon as a critical concentration has been reached. This explains the regularity of the rings, but not their geometry. Why the fronts are so smoothly curved and why did they fail to develop larger diameters?
The first question can only be answered by analogy. The rings are sections through three-dimensional surfaces resembling balloons or biological structures shaped by hydrostatic pressure. Accordingly the advancing cementation front must have had the property of a tensile membrane, inside which a differential pressure could build up osmotically. Such a membrane could have been formed by the precipitate itself, but it is also possible that bacteria were involved, whose presence in deep rocks has recently been demonstrated. The size of the balloons would again be limited by a threshold concentration of the dissolved salts, at which growth was stopped by precipitation. As these salts had come from outside, the balloons should become larger where the rock around was impoverished in nutrient salts.
view can be tested, and linked with the Westerstetten sculptures (#
34), by our
second peel from
If the involvement of endolithic bacteria could be confirmed, the shapes of concretions, Westerstetten sculptures and Liesegang Rings may be even biologically mediated. Nevertheless they are controlled by rules of self-organization rather than genomically coded programs. Such processes, however, should also interest evolutionary biologists, because they often provide the raw material on which Darwinian selection can start to operate.
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