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 2:30 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

More Info on attending an event
Academy Village is an active-adult community located off Old Spanish Trail six miles southeast of Saguaro National Park East. Its residents support the Arizona Senior Academy, a non-profit charitable organization whose mission includes offering free concerts and lectures to the public.

These events are held in the Great Room of The ASA Building adjacent to the Academy Village Community Center. Due to the popularity of cultural events, non-residents who wish to ensure priority seating are advised to make reservations by email at or by phone at (520) 647-0980. To learn more about the Academy, go to

Parking for visitors is in the lot behind the Community Center. All parking spaces in front of the Academy building are reserved.

The Destructive Side of Earth’s Evolution: September 2017
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