The northern boundaries of the Pacific Plate have become known as the “Ring of Fire.”

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 a series of four lectures on the Evolution of the Earth in the Great Room of the Arizona Senior Academy, at 3:30 p.m. on four successive Thursdays (Aug. 31, Sep.7, 14, and 21).

In the Sept. 7 session, McCullough will describe the theory of Plate Tectonics and how it drives the constructive processes.  This will lead to a discussion of how Plate Tectonics has changed the way scientists think about and understand geology.

Plate tectonics builds on the concept of continental drift, which holds that the Earth’s lithosphere, the rigid outermost shell of the planet, is composed of seven or eight major plates and numerous minor ones which have been moving over hundreds of millions of years.

The location where two plates meet is called a plate boundary. Plate boundaries are commonly associated with geological events such as earthquakes and the creation of mountains, volcanoes, mid-ocean ridges and oceanic trenches. The majority of the world’s active volcanoes occur along plate boundaries, with the Pacific Plate’s “Ring of Fire” being the most active and widely known today.

Edgar J. McCullough

Subsequent talks will focus on “Destruction of the Earth’s Surface” (Sept. 14) and “Interpreting Earth History” (Sept. 14).

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


Sept. 7: Plate Tectonics and Earth’s Evolution
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