|
A "Circular" Wilson Cycle ?
Like the Rock "Cycle", we might be inclined to take the Wilson "Cycle" literally - that is, that it just goes round and round without getting anywhere - like the model to the right. This circularity also expresses the view of the 19th century Uniformitarian school of thinking, captured best by James Hutton when he said the earth has "no vestige of a beginning, and no prospect of an end." He envisioned earth processes going round and round but never getting anywhere, never evolving.But, the earth is not just a rock cycle, it is an evolutionary rock cycle. That is, it is not just cyclical, but it is cyclical with direction. The direction we see in the earth's evolution shows up in a number of ways, the increasing diversification of rocks with time, the increasing size of the continental masses (increasing volume of granite), and the changing tectonic provinces we see. The Wilson "Cycle" below captures the evolutionary nature of the processes by showing that the system does not close back on itself completely, but at the end sends a branch out of the circle because of the evolution that has taken place.   pdf version for printing Go to Full Wilson Model
|