The work of running water, in this case the Colorado River, created the Grand Canyon.

For a long time, geology was considered an art and not a science, the reason being that geology was mainly a descriptive activity. It lacked any meaningful quantitative approach and did not have a unifying theory that would tie together the various geologic processes. This changed in the mid-1960s with the acceptance of the theory of plate tectonics as well as various quantitative techniques.

Professor Edgar J. MCullough, a retired member of the University of Arizona Department of Geosciences, will present the third of four lectures on the Evolution of the Earth in the Great Room of the Arizona Senior Academy, at 3:30 p.m. Thursday (Sept.7).

In the Sept. 14 session, McCullough will discuss “Destruction of the Earth’s Surface,” in which he will describe the many forces which alter the planet’s surface.

The energy for destructive processes is derived from the nuclear reactions taking place in the sun along with the Earth’s gravity. Very important chemical changes take place during the operation of these processes. The processes include the work of running water, ground water, landslides, mud flows, creep, wind, shoreline processes and glaciers. These have been studied for years and a great deal is known about each of them because of their effect on people living on the surface.

Edgar J. McCullough

The fourth and final talk in the series is entitled “Interpreting Earth History” and will be presented on Sept. 21.

McCullough began teaching at the UA in the 1960s later became head of the UA Geosciences Department and dean of the College of Science.

Written by Charles Prewitt, Academy Village Volunteer

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Sept. 14: The Destructive Side of Earth’s Evolution
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